CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 62/882,139, titled “SYSTEMS AND METHODS FOR CUFFLESS PLANTAR-BASED BLOOD PRESSURE MEASUREMENT” and filed on August 2, 2019, the entire contents of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to blood pressure measurement. In particular, the present disclosure relates to cuffless blood pressure measurement.

Approximately 75 million or 1 in 3 Americans have hypertension which has traditionally been defined as a systolic blood pressure (SBP) greater than 140 mmHg or a diastolic blood pressure (DBP) greater than 90 mmHg. More recently, the American College of Cardiology and American Heart Association have published guidelines redefining hypertension as a SBP greater than 130 mmHg or DBP greater than 80 mmHg resulting in an increase in prevalence of hypertension in the American population estimated at 46%. Moreover, only half of people with hypertension have their blood pressure under control. Hypertension is a risk factor for heart disease, stroke and kidney disease and was the primary or contributing cause of death in about 410,000 Americans in 2014 (http://wonder.cdc.gov/ucd-icd10.html).

Blood pressure is commonly measured using a sphygmomanometer which consists of an inflatable cuff, a means of inflating the cuff either with a manual or electric pump and instrumentation for measuring pressure such as a mercury manometer or aneroid gauge. To measure blood pressure, the cuff is fastened around the upper arm of the subject and insufflated thereby producing a pressure on the soft tissues of the arm including the underlying brachial artery. A stethoscope is commonly employed and used to auscultate the brachial artery in the antecubital fossa which is distal to the cuff. At a point when the pressure produced by the cuff exceeds the SBP within the brachial artery, no audible sound is detected. As the cuff is slowly deflated to a pressure just below SBP, blood will begin to flow past the cuff, and the sound of turbulent blood flow (Korotkoff sounds) will be detected in the brachial artery allowing measurement of the SBP. As the pressure within the cuff is decreased further to a level below the DBP, the sound of turbulent blood flow will disappear altogether allowing the DBP to be read. This auscultatory blood pressure measurement is commonly used by healthcare providers and is still considered the gold standard for non-invasive blood pressure measurement.

The measurement of blood pressure at home or the ambulatory setting has a number of advantages over measurements made at a health care facility. Firstly, it enables more frequent blood pressure measurements which can more accurately characterize a subject’s blood pressure which may change throughout the day or between days. This could provide a more accurate diagnosis of hypertension or a better evaluation of the effectiveness of therapies targeting hypertension.

Additionally, some subjects experience “white coat” syndrome or elevation of blood pressure which occurs when blood pressure is measured by medical staff which could result in a false positive and an incorrect diagnosis of hypertension in a normal subject.

One of the most common methodologies for ambulatory blood pressure measurement is using an automatic blood pressure monitor. These typically consist of a cuff that can be placed around the upper extremity. The cuff is insufflated by a pump and the blood pressure measurement commonly ascertained using oscillometry. While blood pressure measurement using this methodology is simpler than auscultatory blood pressure measurement by a health care professional, compliance with home blood pressure measurement remains a problem. One potential reason is that measuring blood pressure with an automatic blood pressure monitor requires addition of this activity into the daily routine. It also requires the subject to manually place the cuff around his/her arm in order to make a measurement which is inconvenient and may be difficult for patients with physical or cognitive impairment.

A device which could measure blood pressure without a cuff could have a number of advantages which could improve subject compliance. First, cuffless blood pressure devices could be used to measure blood pressure without the need for the subject to perform the steps of placing and fastening the blood pressure cuff.

Second, the elimination of a pump and cuff, will reduce the cost and bulkiness of the device and enable a device which is potentially more cost effective, wearable or more portable. Finally, cuffless blood pressure measurement could theoretically be done from a body part which is more easily accessible allowing the process of blood pressure measurement to be integrated more easily into the daily routine.

SUMMARY

Systems and methods are provided for measuring blood pressure from the plantar aspect of the foot. In one aspect, a subject stands on a device that includes a platform supporting a sensor assembly such that a surface region of the plantar aspect contacts the distal surface of a sensor assembly supported by the platform. The sensor assembly is configured to measure a signal associated with blood volume or blood flow and a signal associated with applied pressure as the applied pressure is varied. The signals are processed to obtain one or more blood pressure measures. The applied pressure can be varied without muscular exertion by the subject, such as by shifting of the body weight of the subject relative to the sensor assembly and varying the offset of a distal surface of the sensor assembly relative to the platform.

Accordingly, in one aspect, there is provided a method of performing cuffless blood pressure measurement, the method comprising: while a subject stands with a surface region of a plantar aspect of a foot contacting a sensor assembly and a body weight of the subject is shifted such that a pressure applied to the surface region of the plantar aspect by the sensor assembly is varied, employing the sensor assembly to measure: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume or blood flow within the tissue; and a pressure signal, wherein the pressure signal is dependent on the pressure applied to the surface region; and processing the pressure signal and the waveform to determine one or more measures associated with a blood pressure of the subject.

In an example implementation, the method further comprises providing feedback to the subject to assist the subject in shifting their body weight such that a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue.

In an example implementation of the method, the sensor assembly is supported by a platform configured to receive both feet of the subject, and wherein the sensor assembly is positioned relative to the platform such that a distal contact surface of the sensor assembly is contacted by the surface region of the plantar aspect, the method further comprising controlling a tilt mechanism to tilt the platform to facilitate the shift in the body weight of the subject. The platform may be tilted such that a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue. The method may further comprise controlling a tilt rate of the platform such that a rate of change of pressure is less than 6 mm Hg/s. The method may further comprise estimating a mean arterial pressure; and controlling a tilt rate of the platform such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure.

In an example implementation of the method, the method may further comprising providing, to the subject, an indication of a preferred orientation of the foot relative to the sensor assembly. The indication may be dependent on a foot size of the subject. The indication may be configured such that when the foot of the subject is oriented in the preferred orientation relative to the sensor assembly, the sensor assembly is proximal to a selected artery. The indication may be provided in the form of a foot outline. The indication may be provided by a plurality of display elements. The preferred orientation may correspond to a previous foot orientation employed during a previous blood pressure measurement. The previous foot orientation may be determined based on signals detected, during the previous blood pressure measurement, with a sensor array surrounding the sensor assembly.

In an example implementation of the method, the waveform is a plethysmographic waveform, and wherein the pressure signal and the plethysmographic waveform are processed to determine a mean arterial pressure, and wherein the mean arterial pressure is employed to determine the one or more measures associated with the blood pressure of the subject. The mean arterial pressure may be obtained by determining a pressure value corresponding to a maximum amplitude of the plethysmographic waveform.

In an example implementation of the method, the pressure signal and the plethysmographic waveform are measured with a pressure-sensing transducer.

In an example implementation of the method, the blood volume or blood flow waveform is measured using a first sensor configured to direct incident energy into the tissue through the surface region and detect reflected or scattered energy; and wherein the pressure signal is measured using a second sensor. The first sensor may be an optical sensor comprising an optical source configured to emit the incident energy and an optical detector configured to detect the reflected or scattered energy. The second sensor may be a piezoelectric transducer.

In an example implementation of the method, the sensor assembly is supported by a platform configured to receive at least the foot of the subject, and wherein the sensor assembly is positionable relative to the platform such that a distal contact surface of the sensor assembly is contacted by the surface region of the plantar aspect, and wherein an offset of the distal contact surface of the sensor assembly is variable relative to the upper surface of the platform, thereby permitting the subject to vary a compressive force applied to the tissue, the method further comprising providing feedback enabling the subject to determine a suitable offset of the distal contact surface for which a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue.

In an example implementation of the method, the sensor assembly is supported relative to a platform by a compliant mechanism, such that a distal contact surface of the sensor assembly is biased against the surface region of the plantar aspect by said compliant mechanism when the foot is supported on the platform.

In an example implementation, the method further comprises employing a heater supported relative to deliver heat to the foot. The heater may be controlled according to a feedback signal. A temperature sensor may be employed to measure a temperature of the foot, and wherein the feedback signal generated based on a temperature signal measured from said temperature sensor. The feedback signal may be generated based on one or more measures associated with the waveform.

In another aspect, there is provided a method of performing cuffless blood pressure measurement with a blood pressure measurement device, the blood pressure measurement device comprising: a platform configured to receive at least a foot of a subject; and a sensor assembly supported relative to the platform such that a distal contact surface of the sensor assembly is contactable with a plantar aspect of the foot when the foot is supported by the platform; the method comprising: while the subject stands with at least the foot supported by the platform such that a surface region of the plantar aspect contacts the distal contact surface of the sensor assembly, varying a pressure applied by the distal contact surface of the sensor assembly to the surface region while maintaining a constant contact area between the surface region and the distal contact surface, thereby compressing a tissue region proximal to the surface region; and employing the sensor assembly to measure, at a plurality of pressures applied by the distal contact surface: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume or blood flow within the tissue; and a pressure signal, wherein the pressure signal is dependent on the time-dependent pressure applied to the surface region; and processing the pressure signal and the waveform associated with the plurality of pressures to determine one or more measures associated with a blood pressure of the subject. In an example implementation of the method, the pressure applied to by the distal contact surface of the sensor assembly to the surface region is varied by controlling an offset of the distal contact surface relative to an upper surface of the platform. The distal contact surface may be rigid and not deform as the offset is varied, despite changes in the pressure. The offset may be varied pneumatically via application of a pneumatic force to a proximal region of the sensor assembly. The offset may be varied by mechanically actuating at least a portion of the sensor assembly. The sensor assembly may be mechanically actuated such that rotational motion of at least a portion thereof is converted into translational motion relative to the upper surface of the platform. The pressure may be varied such that a range of pressures applied to the surface region includes a mean arterial pressure within the tissue. The pressure may be controlled such that the offset such that a rate of change of the pressure is less than 6 mm Hg/s.

In an example implementation of the method, the sensor assembly is supported relative to the platform by a compliant mechanism, such that the distal contact surface of the sensor assembly is biased against the surface region of the plantar aspect by the compliant mechanism when the foot is supported on the platform. The pressure may be varied by controlling an actuator operatively coupled to the compliant mechanism to the pressure applied by the distal contact surface to the surface region. The compliant mechanism may be a spring, wherein the actuator is configured to vary compression of the spring. The compliant mechanism may include a pneumatic chamber, wherein the actuator is configured to vary an internal pressure within the pneumatic chamber.

The compliant mechanism may be configured such that the distal contact surface is biased beyond an upper surface of the platform in the absence of contact with the foot.

A structural stop may be provided to limit a distal offset of the distal contact surface relative to the upper surface of the platform under the bias in the absence of contact with the foot.

In an example implementation, the method further comprises estimating a mean arterial pressure; and controlling a rate variation of the offset such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure.

In an example implementation, the method further comprises providing, to the subject, an indication of a preferred orientation of the foot relative to the sensor assembly. The indication may be dependent on a foot size of the subject. The indication may be configured such that when the foot of the subject is oriented in the preferred orientation relative to the sensor assembly, the sensor assembly is proximal to a selected artery. The indication may be provided in the form of a foot outline. The indication may be provided by a plurality of display elements. The preferred orientation may correspond to a previous foot orientation employed during a previous blood pressure measurement. The previous foot orientation may be determined based on signals detected, during the previous blood pressure measurement, with a sensor array surrounding the sensor assembly.

In an example implementation of the method, the waveform is a plethysmographic waveform, and wherein the pressure signal and the plethysmographic waveform are processed to determine a mean arterial pressure, and wherein the mean arterial pressure is employed to determine the one or more measures associated with the blood pressure of the subject. The mean arterial pressure may be obtained by determining a pressure value corresponding to a maximum amplitude of the plethysmographic waveform.

In an example implementation of the method, the pressure signal and the waveform are measured with a pressure-sensing transducer.

In an example implementation of the method, the waveform is measured using a first sensor configured to direct incident energy into the tissue through the surface region and detect reflected or scattered energy; and wherein the pressure signal is measured using a second sensor. The first sensor may be an optical sensor comprising an optical source configured to emit the incident energy and an optical detector configured to detect the reflected or scattered energy. The second sensor may be a piezoelectric transducer.

In an example implementation, the method may comprise employing a heater supported relative to deliver heat to the foot. The heater may be controlled according to a feedback signal. A temperature sensor may be employed to measure a temperature of the foot, and wherein the feedback signal generated based on a temperature signal measured from said temperature sensor. The feedback signal may be generated based on one or more measures associated with the waveform.

In another aspect, there is provided a method of performing cuffless blood pressure measurement with a blood pressure measurement device, the blood pressure measurement device comprising: a platform configured to receive at least a foot of a subject; a sensor assembly supported relative to the platform such that a distal contact surface of the sensor assembly is contactable with a surface region of a plantar aspect of the foot when the foot is supported by the platform, the sensor assembly comprising: a first sensor configured to direct incident energy through the surface region into tissue residing proximal to the surface region and detect reflected or scattered energy having encoded therein a waveform; and a second sensor configured to detect a pressure signal dependent on a pressure applied to the surface region; wherein an offset of the distal contact surface is variable relative to an upper surface of the platform; the method comprising: while the subject stands with at least the foot supported by the platform such that the surface region of the plantar aspect contacts the distal contact surface of the sensor assembly, varying the offset of the distal contact surface of the sensor assembly relative to the upper surface of the platform such that a pressure applied to the surface region by the distal contact surface is varied, thereby compressing a tissue region proximal to the surface region; and employing the sensor assembly to measure, at a plurality of offsets of the distal contact surface relative to the upper surface of the platform: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume or blood flow within the tissue; and a pressure signal, wherein the pressure signal is dependent on the time-dependent pressure applied to the surface region; and processing the pressure signal and the waveform associated with the plurality of offsets determine one or more measures associated with a blood pressure of the subject.

In another aspect, there is provided a system for performing cuffless blood pressure measurement, the system comprising: a platform configured to receive at least a foot of a subject; a sensor assembly supported relative to the platform such that a distal contact surface of the sensor assembly is contactable with a plantar aspect of the foot when the foot is supported by the platform; and processing and control circuitry operatively coupled to the sensor assembly, the processing and control circuitry comprising at least one processor and memory operatively coupled to the at least one processor, wherein at least one processor is configured to execute instructions stored within the memory for performing operations comprising: detecting a subject standing with a surface region of the plantar aspect of a foot contacting the sensor assembly; employing the sensor assembly to measure, while a body weight of the subject is shifted such that a pressure applied to the surface region of the plantar aspect by the sensor assembly is varied: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume or blood flow within the tissue; and a pressure signal, wherein the pressure signal is dependent on the pressure applied to the surface region; and processing the pressure signal and the waveform to determine one or more measures associated with a blood pressure of the subject.

In an example implementation of the system, the processing and control circuitry is further configured to provide feedback to the subject to assist the subject in shifting their body weight such that a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue.

In an example implementation of the system, the platform is configured to receive both feet of the subject, the system further comprising a tilt mechanism configured to vary a tilt of the platform, wherein the processing and control circuitry is operatively coupled to the tilt mechanism, and wherein the processing and control circuitry is further configured to control the tilt mechanism to tilt the platform to facilitate the shift in the body weight of the subject. The processing and control circuitry may be further configured to control the tilt mechanism to tilt the platform such that a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue. The processing and control circuitry may be further configured to control a tilt rate of the platform such that a rate of change of pressure is less than 6 mm Hg/s. The processing and control circuitry may be further configured to: estimate a mean arterial pressure and control a tilt rate of the platform such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure.

In an example implementation of the system, the sensor assembly is configured such that the waveform is a plethysmographic waveform, and wherein the processing and control circuitry is further configured to process the pressure signal and the plethysmographic waveform to determine a mean arterial pressure, and to employ the mean arterial pressure to determine the one or more measures associated with the blood pressure of the subject. The processing and control circuitry may be further configured to determine the mean arterial pressure by determining a pressure value corresponding to a maximum amplitude of the plethysmographic waveform.

In an example implementation of the system, the sensor assembly comprises a pressure-sensing transducer, and wherein the processing and control circuitry is further configured such that the pressure signal and the waveform are measured with the pressure-sensing transducer.

In an example implementation of the system, the sensor assembly comprises a first sensor configured to direct incident energy into the tissue through the surface region and detect reflected or scattered energy having the waveform encoded therein; and a second sensor configured to detect the pressure signal. The first sensor may be an optical sensor comprising an optical source configured to emit the incident energy and an optical detector configured to detect the reflected or scattered energy. The second sensor may be a piezoelectric transducer.

In an example implementation of the system, an offset of the distal contact surface of the sensor assembly is variable relative to an upper surface of the platform, thereby permitting the subject to vary a compressive force applied to the tissue, wherein the processing and control circuitry is further configured to provide feedback enabling the subject to determine a suitable offset of the distal contact surface for which a range of pressures applied to the surface region as the body weight is shifted includes a mean arterial pressure within the tissue.

In an example implementation, the system further comprises a plurality of display elements supported by the platform, wherein the plurality of display elements are operably coupled to the processing and control circuitry, and wherein the processing and control circuitry is configured to control the plurality of display elements to provide, to the subject, an indication of a preferred orientation of the foot relative to the sensor assembly. The processing and control circuitry may be configured to control the plurality of display elements such that the indication is dependent on a foot size of the subject.

The processing and control circuitry may be configured to control the plurality of display elements to generate the indication such that when the foot of the subject is oriented in the preferred orientation relative to the sensor assembly, the sensor assembly is proximal to a selected artery. The processing and control circuitry may be configured to control the plurality of display elements such that the indication is provided in the form of a foot outline. The processing and control circuitry may be configured to control the plurality of display elements such that the preferred orientation corresponds to a previous foot orientation employed during a previous blood pressure measurement. A sensor array may be supported by the platform, wherein the sensor array is operably coupled to the processing and control circuitry, and wherein the processing and control circuitry is configured such that the previous foot orientation is determined based on signals detected, during the previous blood pressure measurement, by the sensor array.

In an example implementation of the system, the sensor assembly is supported relative to the platform by a compliant mechanism, such that the distal contact surface of the sensor assembly is biased against the surface region of the plantar aspect by the compliant mechanism when the foot is supported on the platform.

In an example implementation, the system may further comprise a heater supported relative to the platform for delivering heat to the foot when the foot contacts the platform. The heater may be operatively coupled to the processing and control circuitry and wherein the heater is controlled according to a feedback signal. The system may include a temperature sensor configured to measure a temperature of the foot when the foot contacts the platform, wherein the temperature sensor is operatively coupled to the processing and control circuitry, and wherein the feedback signal generated based on a temperature signal measured from the temperature sensor. The feedback signal may be generated based on one or more measures associated with the waveform.

In another aspect, there is provided a system for performing cuffless blood pressure measurement, the system comprising: a platform configured to receive at least a foot of a subject; a sensor assembly supported relative to the platform such that a distal contact surface of the sensor assembly is contactable with a surface region of a plantar aspect of the foot when the foot is supported by the platform; an actuator operatively coupled to the sensor assembly for varying a pressure applied by the distal contact surface of the sensor assembly to the surface region of the plantar aspect of the foot while maintaining a constant area of the distal contact surface; and processing and control circuitry operatively coupled to the sensor assembly and the actuator, the processing and control circuitry comprising at least one processor and memory operatively coupled to the at least one processor, wherein at least one processor is configured to execute instructions stored within the memory for performing operations comprising: detecting the subject standing with at least the foot supported by the platform; controlling the actuator to vary the pressure applied to the surface region by the distal contact surface, thereby compressing a tissue region proximal to the surface region; obtaining, from the sensor assembly, at a plurality of pressures applied by the distal contact surface: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume or blood flow within the tissue; and a pressure signal, wherein the pressure signal is dependent on the time-dependent pressure applied to the surface region; and processing the pressure signal and the waveform associated with the plurality of pressures determine one or more measures associated with a blood pressure of the subject.

In an example implementation of the system, the actuator is configured to vary an offset of the distal contact surface relative to an upper surface of the platform. The distal contact surface may be rigid and not deform as the offset is varied, despite changes in the pressure. The actuator may be configured such that the offset is varied pneumatically via application of a pneumatic force to a proximal region of the sensor assembly. The actuator may be configured such that the offset is varied by mechanically actuating at least a portion of the sensor assembly. The actuator may be configured to mechanically actuate the sensor assembly such that wherein rotational motion of at least a portion of the sensor assembly is converted into translational motion relative to the upper surface of the platform.

In an example implementation of the system, the actuator is configured to vary the pressure such that a range of pressures applied to the surface region includes a mean arterial pressure within the tissue.

In an example implementation of the system, the processing and control circuitry is further configured to control actuation of the actuator such that a rate of change of pressure is less than 6 mm Hg/s.

In an example implementation of the system, the sensor assembly is supported relative to the platform by a compliant mechanism, such that the distal contact surface of the sensor assembly is biased against the surface region of the plantar aspect by the compliant mechanism when the foot is supported on the platform. The actuator may be operatively coupled to the compliant mechanism for varying the pressure applied by the distal contact surface to the surface region of the plantar aspect of the foot when the foot is supported on the platform. The compliant mechanism may be a spring and wherein the actuator is configured to vary compression of the spring. The compliant mechanism may be configured such that the distal contact surface is biased beyond an upper surface of the platform in the absence of contact with the foot. The system may include a structural stop limiting a distal offset of the distal contact surface relative to the upper surface of the platform under the bias in the absence of contact with the foot.

In an example implementation of the system, the processing and control circuitry is further configured to estimate a mean arterial pressure and control a rate variation of the offset such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure.

In an example implementation, the system further comprises a plurality of display elements supported by the platform, wherein the plurality of display elements are operably coupled to the processing and control circuitry, and wherein the processing and control circuitry is configured to control the plurality of display elements to provide, to the subject, an indication of a preferred orientation of the foot relative to the sensor assembly. The processing and control circuitry may be configured to control the plurality of display elements such that the indication is dependent on a foot size of the subject. The processing and control circuitry may be configured to control the plurality of display elements to generate the indication such that when the foot of the subject is oriented in the preferred orientation relative to the sensor assembly, the sensor assembly is proximal to a selected artery. The processing and control circuitry may be configured to control the plurality of display elements such that the indication is provided in the form of a foot outline. The processing and control circuitry may be configured to control the plurality of display elements such that the preferred orientation corresponds to a previous foot orientation employed during a previous blood pressure measurement. The system may include a sensor array supported by the platform, wherein the sensor array is operably coupled to the processing and control circuitry, and wherein the processing and control circuitry is configured such that the previous foot orientation is determined based on signals detected, during the previous blood pressure measurement, by the sensor array.

In an example implementation of the system, the sensor assembly is configured such that waveform is a plethysmographic waveform, and wherein the processing and control circuitry is configured to process the pressure signal and the plethysmographic waveform to determine a mean arterial pressure, and to employ the mean arterial pressure to determine the one or more measures associated with the blood pressure of the subject. The processing and control circuitry may be configured to determine the mean arterial pressure by determining a pressure value corresponding to a maximum amplitude of the plethysmographic waveform.

In an example implementation of the system, the sensor assembly comprises a pressure-sensing transducer and wherein the processing and control circuitry is configured to measure the pressure signal and the waveform with the pressure sensing transducer.

In an example implementation of the system, the sensor assembly comprises a first sensor configured to direct incident energy into the tissue through the surface region and detect reflected or scattered energy having the waveform encoded therein; and a second sensor configured to detect the pressure signal. The first sensor may be an optical sensor comprising an optical source configured to emit the incident energy and an optical detector configured to detect the reflected or scattered energy. The second sensor may be a piezoelectric transducer.

In an example implementation, the system further comprises a heater supported relative to the platform for delivering heat to the foot when the foot contacts the platform. The heater may be operatively coupled to the processing and control circuitry and wherein the heater is controlled according to a feedback signal. The system may further comprise a temperature sensor configured to measure a temperature of the foot when the foot contacts the platform, wherein the temperature sensor is operatively coupled to the processing and control circuitry, and wherein the feedback signal generated based on a temperature signal measured from the temperature sensor. The feedback signal may be generated based on one or more measures associated with the waveform.

In another aspect, there is provided a system for performing cuffless blood pressure measurement, the system comprising: a platform configured to receive at least a foot of a subject; a sensor assembly supported relative to the platform such that a distal contact surface of the sensor assembly is contactable with a surface region of a plantar aspect of the foot when the foot is supported by the platform, the sensor assembly comprising: a first sensor configured to direct incident energy through the surface region into tissue residing proximal to the surface region and detect reflected or scattered energy having encoded therein a waveform dependent on changes in blood volume or blood flow; and a second sensor configured to detect a pressure signal dependent on a pressure applied to the surface region; wherein an offset of the distal contact surface is variable relative to an upper surface of the platform; an actuator for varying the offset of the distal contact surface relative to the upper surface of the platform; and processing and control circuitry operatively coupled to the sensor assembly and the actuator, the processing and control circuitry comprising at least one processor and memory operatively coupled to the at least one processor, wherein at least one processor is configured to execute instructions stored within the memory for performing operations comprising: detecting the subject standing with at least the foot supported by the platform such that the surface region of the plantar aspect contacts the distal contact surface of the sensor assembly; controlling the actuator to vary the offset of the distal contact surface of the sensor assembly relative to the upper surface of the platform such that a pressure applied to the surface region by the distal contact surface is varied, thereby compressing a tissue region proximal to the surface region; controlling the sensor assembly to measure, at a plurality of offsets of the distal contact surface relative to the upper surface of the platform: a waveform associated with tissue residing proximal to the surface region, the waveform being dependent on temporal changes in blood volume within the tissue; and a pressure signal, wherein the pressure signal is dependent on the time-dependent pressure applied to the surface region; and processing the pressure signal and the waveform associated with the plurality of offsets determine one or more measures associated with a blood pressure of the subject.

A further understanding of the functional and advantageous aspects of the disclosure can be realized by reference to the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the drawings, in which:

FIG. 1 shows an example of a device for performing plantar-based blood pressure measurement.

FIG. 2 shows an example of an integrated sensor that includes a first sensor for measuring a signal dependent on changes in blood volume or blood flow and a second sensor for measuring pressure. FIG. 3 shows the major arteries in the plantar aspect.

FIGS. 4A-4C plot (A) the time-dependence of an example photo- plethysmographic waveform, (B) the corresponding time-dependence pressure applied to a plantar region, and (C) the resulting relationship between applied pressure and oscillometric amplitude of the photo-plethysmographic waveform.

FIG. 5 plots the measured pressure applied to a region of the plantar aspect during shifting of the body weight of a subject.

FIGS. 6A-6C illustrate example maneuvers for varying the body weight of a subject relative to distal surface of a sensor assembly contacting a plantar aspect.

FIGS. 7A and 7B show a flow chart illustrating an example method of performing plantar-based oscillometric blood pressure measurement.

FIGS. 8A-8D illustrate an example embodiment for plantar-based blood pressure measurement in which a varying pressure is applied to a region of the plantar aspect via controlled offset of the distal surface of the sensor assembly relative to the upper surface of the platform.

FIGS. 8E-8J illustrate example devices incorporating a compliant (restoring) mechanism to modulate the force applied to the plantar aspect.

FIG. 9 shows an example device that facilitates user guidance of foot placement prior to plantar-based blood pressure measurement.

FIG. 10 schematically illustrates an example system for performing plantar- based blood pressure measurements.

FIGS. 11A-11C plot experimental results demonstrating the measurement of blood pressure from the lateral plantar artery using an example derivative-based processing algorithm.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well- known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not be construed as preferred or advantageous over other configurations disclosed herein.

As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms “about” and “approximately” mean plus or minus 25 percent or less.

It is to be understood that unless otherwise specified, any specified range or group is as a shorthand way of referring to each and every member of a range or group individually, as well as each and every possible sub-range or sub-group encompassed therein and similarly with respect to any sub-ranges or sub-groups therein. Unless otherwise specified, the present disclosure relates to and explicitly incorporates each and every specific member and combination of sub-ranges or subgroups.

As used herein, the term "on the order of", when used in conjunction with a quantity or parameter, refers to a range spanning approximately one tenth to ten times the stated quantity or parameter.

Various embodiments of the present disclosure provide systems, devices and methods for cuffless blood pressure measurement and/or monitoring based on measurements involving the plantar aspect of the foot, in which the subject’s own weight is employed to apply, and in some example embodiments, to modulate, the pressure applied to a sensor assembly while recording signals dependent on changes in arterial blood volume or blood flow.

An example embodiment of a device that can be employed to perform plantar-based blood pressure measurement is illustrated in FIG. 1. The example device, shown in an overhead view, includes a platform 100 (e.g. a housing or enclosure) having an upper surface configured to receive at least one foot of a user. As shown in the figure, a sensor assembly 110 is supported, relative to the platform 100, such that a distal contact surface of the sensor assembly 110 is contacted with a surface region of the plantar aspect of the foot when the user stands with the foot on the platform with the plantar aspect positioned over the sensor assembly. The sensor assembly is operably coupled to processing circuitry 400 and a power supply or source 160. The example device may also include a display 170 that is operably coupled to the processing circuitry.

In some example embodiments, the device may be a weight scale that is configured to provide a measure of weight and one or more measures of blood pressure. Weigh scales are a common household appliance and used by millions of people worldwide. Additionally, there is a direct and potentially causal relationship between obesity and high blood pressure in a majority of subjects with essential hypertension. Estimates from the Framingham Heart Study, for example, indicate that 78% of primary hypertension in men and 65% of primary hypertension in women can be attributed to excess weight. The ability to measure blood pressure using a weigh scale may provide a means of measuring two inter-related and important health measures, weight and blood pressure, in a convenient way using a device that has an established place in the American household.

In some example embodiments, the sensor assembly 110 includes at least two sensors: (i) a first sensor that detects changes in blood volume (e.g. a plethysmographic sensor) or blood flow and generates a waveform associated with tissue residing proximal to the surface region of the plantar aspect that contacts the distal surface of the sensor assembly and (ii) a pressure sensor that generates a signal dependent on a pressure applied to the surface region by the distal surface of the sensor assembly. In some example embodiments, the arterial blood flow or blood volume sensor may also be capable of detecting a pressure-dependent signal, and thus a single sensor may be employed to measure both the signal dependent on changes in arterial blood volume (or blood flow) and the pressure signal. Various example embodiments involving such dual- and single-sensor configurations are described in detail below.

In some example implementations, the platform 100, the sensor assembly 110, or a combination thereof may be employed to provide heat to the plantar aspect of the foot, in order to avoid or reduce vasoconstriction of vessels of the feet that can otherwise result in reduction in the measured waveform. For example, this could be achieved through an electric radiant heater consisting of a mesh or circuit of looped wire/conductor embedded within the platform or sensor assembly. Alternatively, this could be achieved with a hydronic radiant heater consisting of a circuit of tubing carrying fluid warmed by an electric heater. In some example implementations, the amount of heat provided may be controlled according to a feedback based on a measured signal. For example, in one example implementation, the amount of heat provided may be controlled according to an amplitude of a detected waveform (e.g. supplying heat if a value, such as the amplitude of a plethysmographic signal, is less than a pre-determined threshold). In another example implementation, a temperature sensor may be included to measure a temperature of the plantar aspect and the heating of the plantar aspect by the integrated heater may be controlled to raise the temperature of the plantar aspect beyond a pre-determined temperature value.

An example dual-sensor configuration is shown in FIG. 2. The distal (upper) surface 115 of the sensor assembly 110 shown in FIG. 2 is visible in FIG. 1 , while the remainder of the sensor assembly 110 is recessed below the upper surface of the platform 100 in FIG. 1. The example sensor assembly 110 shown in FIG. 2 includes a first sensor 120 configured to detect changes in arterial blood volume (or blood flow) and a second sensor 130 configured to measure pressure. The pressure sensor 130 measures pressure applied by the distal surface 115 of the sensor assembly 110 to the surface region of plantar aspect of the foot. Non-limiting examples of suitable pressure sensors include a strain gauge load cell, piezoelectric load cell, hydraulic load cell, pneumatic load cell and a capacitive load cell.

As noted above, the first sensor 120 is configured to detect changes in blood volume or blood flow and generate a waveform associated with tissue residing proximal to the surface region that contacts the distal surface 115 of the sensor assembly 110 when the user stands with a plantar aspect of the foot contacting the distal surface 115. The waveform measured by the first sensor 120 is thus dependent on temporal changes in blood volume or blood flow within the tissue, and may be processed according to a processing modality such as, but not limited to, oscillometry. As shown in FIG. 3, the plantar aspect of the foot is highly vascularized and supplied by several large arteries including the medial 10 and lateral 20 plantar arteries, and the plantar arch 30. The lateral plantar artery approaches the plantar aspect of the foot and is well-suited for evaluation. There are additional superficial branches such as the superficial branch of the medial plantar artery which are also readily accessible from the plantar aspect of the foot and can also serve as a target.

It will be understood that while many of the example embodiments described above refer to a photo-plethysmography (PPG) sensor for detection of the waveform, the first sensor 120 can be implemented according to a wide range of detection modalities. In some example implementations, the first sensor 120 is a reflectancemode photo-plethysmography sensor. FIG. 2 illustrates a non-limiting example of a PPG sensor that includes a light emitting diode and an optical sensor such as a photodiode. A PPG sensor may employ electromagnetic radiation according to a wide range of optical wavelengths including visible and infrared radiation. Other nonlimiting examples of suitable plethysmographic sensors include sensors based on mechanical, mechanoelectric, acoustic, electrical, and magnetic properties of tissue. In addition to plethysmographic sensors, which measure changes in blood volume, sensors which measure changes in blood flow such as Doppler ultrasound may be used. In some example embodiments, an array of blood volume (or blood flow) sensors and pressure sensors may be employed to measure blood volume (or blood flow) and pressure simultaneously at multiple points on one foot or both feet of a user. For example, a PPG signal may be acquired using a camera or array of cameras. It will also be understood that while some modalities such as Doppler ultrasound have greater specificity for detecting pulsatile flow from an underlying artery, other modalities such as PPG are less specific and may detect pulsatile blood volume changes related to a single large artery but also from a plurality of smaller vessels in the vicinity or remote from a specified large artery.

In some example embodiments, the blood flow/volume waveform may be processed, along with a measure of applied pressure, according to an oscillometric method to determine one or more measures associated with the blood pressure of the user. For example, estimates of SBP and DBP may be determined by processing a plethysmographic waveform (oscillogram) and the applied pressure, as the difference in the plethysmographic waveform between systole and diastole provides a measurement of the blood volume oscillation. By applying the variable pressure on the sole of the foot through a range of pressures above and below the mean arterial pressure and correlating this applied pressure with blood volume oscillation of the plethysmographic waveform, an oscillogram can be calculated. An example of an oscillogram is shown in FIGS. 4A and 4B. For example, the mean arterial pressure (MAP) may be identified as the measured applied pressure that corresponds to a peak amplitude of the plethysmographic waveform, as shown in FIGS. 4A and 4B. The mean arterial pressure may be employed to determine one or more additional measures associated with the blood pressure of the user.

One methodology for calculating SBP and DBP from the oscillogram is the Standard Fixed-Ratio method. In this methodology, the MAP is estimated as the applied pressure at which the blood volume oscillation is maximal (AM). AS and AD are the amplitudes of the oscillogram when the applied pressure is equal to systole and diastole, respectively. For a population, the ratio of AS/AM and AD/AM are typically a fixed value, thereby allowing the SBP or DBP to be estimated from the oscillogram based on an estimated MAP from oscillometry, as illustrated in FIG. 4C. For brachial artery measurements AS/AM and AD/AM are 0.55 and 0.85 respectively. Similar population-based ratios have been found for finger measurements and it follows that suitable population-based ratios for the foot can also be ascertained.

In addition or alternative to the oscillometric method, the plethysmographic or blood flow waveform may be processed along with a measure of applied pressure to directly determine one or more measures associated with the blood pressure of the user. For example, when the applied pressure is greater than SBP at the plantar aspect, the waveform is abolished during the entire cardiac cycle due to occlusion of the artery. If the applied pressure is slowly reduced, the waveform will re-appear during systole when the applied pressure is less than SBP, allowing a measurement of SBP. As the applied pressure is reduced further to just below the DBP at the plantar aspect, when normal blood flow is restored in the artery, the waveform will be present during both systole and diastole. Hydrostatic corrections may then be applied to these blood pressure measures.

While known methods of performing cuffless blood pressure measurement involve the active application of muscular force to a sensor, various example embodiments of the present disclosure take advantage of the passive pressure generated by the body weight of the user, and the variation of this passive pressure, to provide a time-varying pressure for performing oscillometric measurements of a plantar aspect of the foot.

In one example embodiment involving passively applied and gravitationally assisted time-varying pressure, the example device shown in FIGS. 1 and 2 may be employed to generate one or more measures associated with the blood pressure of a user as follows. The user stands with a surface region of the plantar aspect of the foot contacting the distal surface 115 of the sensor assembly 110. The user then shifts their body weight to vary a pressure that is applied by the distal surface 115 of the sensor assembly 110 to the surface region of the plantar aspect. As the user’s body weight is shifted, the blood volume (or blood flow) sensor 120 is employed to record a waveform from tissue residing proximal to the surface region of the plantar aspect of the foot and the pressure sensor 130 is employed to detect a pressure signal that can be processed to determine a measure associated with the pressure applied to the surface region of the plantar aspect by the distal surface 115. The time-varying pressure signal and the waveform may be processed (e.g. via oscillometry or via direct measurement, as described above) to determine one or more measures associated with the blood pressure of the user, such as estimates of the systolic and diastolic blood pressure. As noted above, although FIGS. 1 and 2 illustrate an example implementation involving two distinct sensors for measuring the blood volume/flow waveform and the applied pressure, these measurements may be obtained using a single sensor in alternative embodiments.

According to example implementations involving the use of a plethysmographic sensor, the measured plethysmographic waveform, obtained from tissue proximal to the surface region of the plantar aspect that contacts the distal surface of the sensor assembly, and the measured pressure applied by the distal surface of the sensor assembly to the surface region of the plantar aspect, may be processed to determine MAP _foot , the mean arterial pressure at the plantar aspect of the foot. For example, MAP _foot may be determined by processing the measured plethysmographic waveform and the measured applied pressure to identify an applied pressure that corresponds to one or more features in the plethysmographic waveform. For example, MAP _foot may be identified as the measured applied pressure that corresponds to a peak amplitude of the plethysmographic waveform. Alternatively, for example, MAP _foot may be identified as the measured applied pressure that corresponds to a maximum area under one or more cycles of the plethysmographic waveform. The mean arterial pressure may be employed to determine one or more additional measures associated with the blood pressure of the user.

The mean arterial pressure at the heart, MAP _heart , can be estimated based on a measured or estimated height of the heart relative to the plantar aspect of the foot by accommodating for the hydrostatic pressure difference as follows: AP _h eart ~ MAP _00t — pgh (1) where p is the density of blood, g is gravitational acceleration and h is the height of the heart relative to the foot. One or more blood pressure measures may then be calculated based on MAP _heart , for example, SBP and DBP, for example, using the Standard Fixed-Ratio method. It will be understood, however, that the present disclosure is not intended to be limited to methods involving the Standard Fixed-Ratio method and that other methods for obtaining methods for determining a measure associated with blood pressure based on the measurement and processing of a plethysmographic waveform and applied pressure may be employed in the alternative. For example, while the Standard Fixed-Ratio method may be limited particularly for populations with disease, this limitation can be overcome by methodologies such as the Patient-Specific Algorithm that employs parametric modeling of the oscillogram. It may also be possible to obtain an improved prediction of the SBP and DBP from an oscillogram or other waveform using deep learning methodologies.

In example embodiments involving oscillometric processing of the plethysmographic waveform and the applied pressure, the range of pressures that are applied to the surface region of the plantar aspect contacting the distal surface of the sensor assembly should include MAP _f00t so that the features associated with an applied pressure of MAP _f00t are present in the measured plethysmographic waveform. A key benefit of the present example methods is that by merely shifting the body weight of the user, the pressure to the surface region of the plantar aspect can be readily and controllably altered within a range that includes the mean arterial pressure at the plantar aspect of the foot, as shown below.

For example, for a height of h = 1.4 m and MAP _heart = 93 mmHg for at typical person, it follows that MAP _f00t MAP _foot = 201 mmHg. Accordingly, the applied pressure on the plantar aspect of the foot should be varied within a range that includes a pressure value of approximately 200 mmHg. FIG. 5 plots the recorded time-dependent pressure applied by the distal surface of the sensor assembly to a surface region of a plantar aspect of the foot as the weight of a user was shifted for a user with a heart to foot height of 1.3 m. As the weight of the user is shifted from (i) an initial orientation in which less of the user’s weight is supported by the sensor assembly than the ground or platform contacted by the other foot, to (ii) a final orientation in which the user’s weight is redistributed with more of the user’s weight being supported by the sensor assembly and less of the user’s weight being supported by the ground or platform contacted by the other foot, the recorded applied pressure increases over a range spanning approximately 150 to 275 mmHg. Since this range of 150 to 274 mmHg includes the aforementioned target applied pressure of 200 mmHg that is expected to correspond to MAP _foo u it follows that processing the plethysmographic waveform that corresponds to this range of applied pressure values would result in a successful determination of MAP _foot ·

In other words, an oscillometric measure of MAP _foot can be obtained based on the measurement of a plethysmographic waveform and an applied pressure according to a measurement modality in which the applied pressure is passively generated in a gravitationally-assisted manner merely by the shifting of the user’s weight, without requiring any applied muscular force by the user. The user needs only shift their body without applying a muscular pushing force to the sensor assembly, providing a modality in which the application of the variable force is gravitationally mediated as opposed to being mediated by the application of a force via the exertion of a user. Moreover, the measure of MAP _foot is achieved without the need to surround the anatomy of the user with a cuff or other constriction device.

The present example embodiments can thus be contrasted with known cuffless blood pressure measurement methods that require the user to manually create the necessary pressure on the sensor assembly via the application of an active muscular force. Such methods are disadvantageous in that they require physical effort to exceed the mean arterial pressure that is needed for oscillometry. In some cases, it may be difficult for the user to apply a sufficiently high force in order to achieve the mean arterial pressure, such as hypertensive patients with a very high associated MAP, and patient populations such as frail or ill patients, elderly patients, pediatric patients, and patients with a physical or mental disability. Furthermore, even in cases in which a user is capable of generating a sufficiently high force for oscillometry, the effort to apply such a force may result in exertional increases in blood pressure, thereby comprising the result of the measurement. Another significant disadvantage of such methods is that when measurements are obtained using the finger, the measurements are subject to variability caused by changes in position of the finger relative to the heart, often requiring complex dynamic correction of the hydrostatic effect. In stark contrast, the present example methods do not suffer from these limitations or problems, since they do not require the active application of a muscular force, involve minimal interaction with the user, and do not result in significant dynamic changes of the measurement location relative to the heart.

As described above, in some example embodiments, the user shifts their weight relative to the sensor assembly, optionally assisted with guidance (e.g. guidance with or without feedback), while contacting the distal surface of the sensor assembly, according to a wide range of implementations. FIG. 6A illustrates a first example implementation in which a user places one foot on the platform 100 and contacts a surface region of the plantar aspect of the foot with the distal surface of the sensor assembly, while keeping the remaining foot off the ground. Initially, the user stands such that more of the user’s weight is supported by the ground and less of the user’s weight is supported by the platform. As shown in the figure, the user gradually leans forward, shifting the user’s weight such that the user’s weight is redistributed with less of the user’s weight being supported by the ground and more of the user’s weight being supported by the platform. It will be understood that this maneuver can alternatively be performed in reverse, or, for example, in any combination of forward and reverse.

FIG. 6B illustrates another example maneuver in which the user places one foot on the platform 100 and contacts a surface region of the plantar aspect of the foot with the distal surface of the sensor assembly, with the other foot either on or off the platform, and stands such that more of the user’s weight is supported by the sensor assembly than the ground or platform contacted by the other foot. As shown in the figure, the user gradually leans forward, shifting the user’s weight such that the user’s weight is redistributed with less of the user’s weight being supported by the sensor assembly and more of the user’s weight being supported by the ground or platform contacted by the other foot, raising the foot contacting the sensor assembly (optionally such that at the conclusion of the measurement, the foot no longer contacts the sensor assembly). It will be understood that this maneuver can alternatively be performed in reverse, or, for example, in any combination of forward and reverse.

FIG. 6C illustrates an example maneuver in which the user places one foot on the platform 100 and contacts a surface region of the plantar aspect of the foot with the distal surface of the sensor assembly, with the other foot either on or off the platform (the figure shows an example implementation in which the other foot resides on the platform 100), and stands such that less of the user’s weight is supported by the sensor assembly than the ground or platform contacted by the other foot. As shown in the figure, the user gradually leans sideways, shifting the user’s weight such that the user’s weight is redistributed with more of the user’s weight being supported by the sensor assembly and less of the user’s weight being supported by the ground or platform contacted by the other foot. It will be understood that this maneuver can alternatively be performed in reverse, or, for example, in any combination of forward and reverse.

Although not shown in FIGS. 6A-6C, the user may employ an additional support, such as a cane or a wall, for stability, as the weight of the user is shifted. While the maneuvers shown in FIGS. 6A-6C have been disclosed as separate maneuvers, it will be understood that two or more of the maneuvers may be combined (optionally with other maneuvers than those shown in the figures).

In one example implementation, an offset of the distal contact surface of the sensor assembly may be variable relative to the upper surface of the platform, thereby permitting the subject to select a suitable offset for use during a maneuver, to alter the range of compressive forces applied to the tissue. For example, a suitable offset of the distal contact surface may be selected such that, as the body weight is shifted according to given maneuver of the user, the applied pressure includes, for example, a mean arterial pressure within the tissue near the mid-point of the applied pressure values (for oscillometric measurements), or, for example, the SBP. The data plotted in FIG. 5 was obtained using a distal offset of 2 mm relative to the upper surface of the platform. The distal offset necessary to achieve a sufficiently high pressure may vary depending on the location of the surface region of the plantar aspect. For example, a surface region in the arch region may require a larger offset than a surface region at the heel region of the ball region.

In some example embodiments, the user may be provided with instructions (guidance) to assist the user in performing one or more maneuvers during a measurement phase. For example, the guidance may demonstrate one or more maneuvers for the user to perform. Additionally or alternatively, the guidance may instruct the user to shift their weight at a prescribed rate, or according to a prescribed time duration, or to increase or decrease the relative amount of their body weight that is supported by the sensor assembly. Examples of instructions for guiding a maneuver include text-based instructions, audible instructions or cues, graphical instructions (e.g. animating one or more maneuvers shown in FIGS. 6A-6C, or variations thereof), and tactile/haptic instructions or cues, or a combination of two or more thereof.

In some example implementations, the guidance may provide feedback to the user based on one or more measures such as, but not limited to, one or more of user’s weight, the measured applied pressure, and the measured blood volume or blood flow waveform. For example, in the non-limiting case of oscillometric blood pressure measurement, the measured waveform may be processed while the user shifts their weight, or after the user has shifted their weight, to identify the presence or absence of one or more features corresponding to the MAP. If such features are absent from the measured waveform, the user may be instructed to continue or repeat the shifting of their weight, optionally according to a different maneuver or a different time duration for a given maneuver. In another example embodiment, a target applied pressure that is expected to correspond to the MAP at the plantar aspect ( MAP _foot ) may be computed for a user (e.g. based on a typical MAP _heart and an estimated height of the user) and feedback may be provided to the user to control the shifting of their body weight such that the range of pressures applied to the surface region of the plantar aspect by the distal surface of the sensor assembly includes the target pressure.

FIGS. 7A and 7B illustrate an example method of performing plantar-based blood pressure measurement, using an example system such as the system shown in FIG. 1 in which PPG is employed to measure the plethysmographic waveform. At the commencement of the example method 200, the system is initialized at 205 and the user stands with a surface region of the plantar aspect of a foot contacting the distal surface of the sensor assembly 210.

The user may optionally “login” to the system via input or via detection of a biometric signature, such as, but not limited to, one or more characteristics of a measured plethysmographic waveform, images of the foot or user’s face obtained with an integrated camera, or pressure footprint of the user obtained with an integrated sensor array (e.g. a capacitive touchscreen). The user identity may be optionally confirmed as shown at 215. For example, the user identity may be detected by the device using a biometric signature or a signal from another device, including, but not limited to, a wearable device.

An initial measurement is performed to determine whether a sufficient PPG signal has been obtained at 220 and 225, and in the event that an insufficient PPG signal is detected, the user is instructed to take corrective action at 230 (such as adjusting the position of their foot relative to the sensor assembly) until an adequate PPG signal is detected. When an adequate signal is detected, the method proceeds as shown in FIG. 7B, with the user being instructed to perform one or more maneuvers to vary their weight in relation to the sensor assembly, as shown at 250. The user movements may optionally be guided by instructions, as shown at 255 and as described above. The PPG waveform and applied pressure are measured as the weight of the user is shifted relative to the sensor assembly, as shown at 260. This process may be repeated one or more times if an insufficient PPG waveform has been detected, as shown at 265 and 270. After applying a hydrostatic correction at 280, the one or more blood pressure measures, such as the systolic and diastolic blood pressures are computed and displayed as shown at 285. The hydrostatic correction may be performed based on an estimated height of the heart of the user relative to the plantar aspect. This estimated height may be obtained, for example, via input received from the user, such as a height of the user, and the use of a known scaling factor between total user height and heart height. The estimated height of the heart may alternatively be obtained using other means, such as obtaining an image of the user and processing the image to estimate the heart height. The blood pressure data may be saved according to a wide variety of formats, such as locally on the device and/or on a remote device such as a smartphone and/or remote server. The blood pressure data may be stored in association with a specific user.

While many of the preceding example methods employ the shifting of the body weight of a user to obtain a suitable range of applied pressure while acquiring plethysmographic signals (e.g. a plethysmographic waveform), it will be understood that the body weight of the user may alternatively be shifted in an automated manner. For example, device-assisted shifting of the body weight of the user relative to the sensor assembly may be achieved by controlling a tilt of the platform, such that as the tilt of the platform changes, the weight of the user is responsively shifted relative to the sensor assembly. Such a change in the tilt of the platform may be achieved, for example, via a motor that is housed within the platform, where the motor drives a linear actuator (e.g. a travelling nut linear actuator). The tilt rate may be controlled, for example, such that rate of change of pressure is less than 6 mm Hg/s. In another example implementation, the tilt rate of the platform may be controlled such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure. In example embodiments involving the direct measurement of SBP and DBP via arterial occlusion, the tilt of the platform may be controlled such that the applied pressure range includes the SBP and the DBP.

In some example implementations, one or more measures such as, but not limited to, one or more of user’s weight, the measured applied pressure, and the measured blood volume or flow waveform may be processed to control the tilt of the platform in order to obtain a suitable waveform. For example, in an example embodiment involving oscillometric measurement, the measured plethysmographic waveform may be processed while tilting the platform, or after tilting the platform, to identify the presence or absence of one or more features corresponding to the MAP. If such features are absent from the measured plethysmographic waveform, the platform may be further tilted, or the tilt cycle may be repeated. In another example embodiment, a target applied pressure that is expected to correspond to the MAP at the plantar aspect ( MAP _f00t ) may be computed for a user (e.g. based on a typical MAP _heart and an estimated height of the user) and the tilt of the platform may be controlled such that the measured applied pressure range includes the target applied pressure.

In other example embodiments, a variation in pressure applied to the surface region of the plantar aspect of the foot by the distal surface of the sensor assembly may be generated without requiring that the user shift their weight. Instead, the variation in applied pressure may be facilitated by varying an offset of the distal contact surface of the sensor assembly relative to an upper surface of the platform, thereby applying a variable compressive pressure to tissue residing proximal to the surface region of the plantar aspect that is contacted with the distal surface of the sensor assembly.

The operating principle of this method can be understood with reference FIGS. 8A and 8B. The figures show the side view of a foot residing on the platform 100, with at least a portion of the weight of the user being supported by contact of the foot with the platform. A time-varying applied pressure is generated by controlling the offset of the distal surface of the sensor assembly 115 relative to the upper surface 102 of the platform, with FIG. 8B showing the distal surface 115 extending further, relative to the upper surface of the platform, compared to FIG. 8A. Since the overall contact area between the plantar aspect of the foot and the upper surface 102 of the platform 100 significantly exceeds the area of the distal surface 115 of the sensor assembly, the net force applied by the upper surface 102 of the platform 100 significantly exceeds the net force applied by the distal surface 115 of the sensor assembly in the configuration shown in FIG. 8A. As the offset of the distal surface 115 of the sensor assembly is increased relative to the upper surface 102 of the platform 100, the tissue is compressed and the pressure applied to the surface region of the plantar aspect contacting the distal surface 115 of the sensor assembly increases. The present example embodiment thus achieves a variable applied pressure in a cuffless configuration in a passive manner that is absent of any applied muscular force by the user. In other words, the present example embodiment utilizes a gravitationally assisted and compression-varied pressure and can facilitate the generation of a suitable range of pressures for performing oscillometric blood pressure measurements in the absence of user effort.

It is noted that the example embodiment illustrated in FIGS. 8A and 8B maintains a constant area of the distal surface 115 of the sensor assembly as the distal surface offset is varied relative to the upper surface 102 of the platform 100. This ensures that as the offset is varied and a variable pressure is applied to the plantar region of the foot, the surface region of the plantar region that is contacted by the distal surface 115 does not change, and a common tissue region proximal to the surface region is interrogated. This example embodiment therefore enables the measurement of blood pressure in a cuffless configuration, without requiring exertion from the user, where the tissue region that is probed does not change as the variable pressure is applied, thereby providing a robust and reliable measure of blood pressure. The constancy of the surface area of the distal surface 115, and the ability to maintain a constant contact area between the distal surface 115, may be facilitated by a sensor assembly having a rigid distal contact surface.

As in the case of the preceding example embodiment involving the generation of a variable pressure via the shifting of the user’s body weight, the range of applied pressures should include the MAP _f00t (in the example case of oscillometric based processing) in order to facilitate the detection of features in the plethysmographic waveform that correspond to MAP _f00t · FIG. 8C presents pressure measurements obtained from a user standing with the user’s weight supported by both feet, with the plantar aspect of one foot contacting the distal surface of the sensor assembly. As the offset of the distal surface of the sensor assembly was increased relative to the upper surface of the platform, a range of applied pressures was recorded that spanned approximately 110-290 mmHg. This range includes the aforementioned target applied pressure of 200 mmHg that is expected, for the present example user, to correspond to MAP _foo u thereby demonstrating the feasibility of the present example embodiment for performing cuffless blood pressure measurement. This measured range also includes a typical range of SBP values, thereby also demonstrating the suitable of the present example plantar-based devices and methods for performing direct (i.e. artery-occlusion-based) plantar-based blood pressure measurement.

The offset of the distal surface of the sensor assembly can be varied, relative to the upper surface of the platform, according to many different example implementations. FIG. 8D illustrates one example and non-limiting implementation in which the sensor assembly is mechanically coupled to a screw 190 that is actuated (e.g. via a motor), thereby varying the offset of the distal surface 115 of the sensor assembly 110. Other example actuation mechanisms include, for example, a linear actuator in which the sensor assembly is mechanically coupled to a travelling nut that translates vertically relative to a rotating screw, a pneumatic mechanism in which the sensor assembly is translated, relative to the platform, via a pneumatic force and a hydraulic mechanism in which the sensor assembly is translated, relative to the platform, via a hydraulic force. The variation in the offset of the distal surface may be continuous or stepwise, with a stepwise configuration illustrated in FIG. 8C. Although the example embodiment illustrated in FIGS. 8A and 8B show the offset occurring in a direction that is perpendicular to the upper surface 102 of the platform 100, it will be understood that the offset may alternatively be applied at an angle relative to the upper surface 102.

FIGS. 8E and 8F illustrate an example embodiment in which a compliant mechanism (e.g. a biasing or restoring mechanism) is integrated with the actuation mechanism. The figures illustrate an example implementation in which the sensor assembly 110 (including the PPG and load cell) are mounted onto a spring 140 characterized by a spring constant k. The spring 140 rests on a movable stop 142 (e.g. a plate) which is biased against, or integrated with, a nut 144 that is threaded on and longitudinally extendable along a screw 146, the screw being rigidly supported relative to the platform. As in the preceding example embodiments, since the overall contact area between the plantar aspect of the foot and the upper surface 102 of the platform 100 significantly exceeds the area of the distal surface 115 of the sensor assembly, the net force applied by the upper surface 102 of the platform significantly exceeds the net force applied by the distal surface 115 of the sensor assembly in the configuration shown in FIG. 8A.

As shown in FIG. 8E, in the absence of the application of a downward force by a user (the plantar aspect of the user is not yet contacting the distal surface 115 of the sensor assembly 110), the distal surface 115 of the sensor assembly 110 rests a distance Dc above the surface 102 of the platform (i.e. the spring applies a restoring force to the sensor assembly 110). A structural stop 150 may be integrated with the platform 110 to contact the sensor assembly or a feature extending therefrom in order to limit the travel of the distal surface 115 of the sensor assembly in a distal direction beyond the top surface 102 of the platform, as shown in FIG. 8E. The structural stop may maintain some level of compression of the spring in the absence of contact with the plantar aspect of the foot of a user.

When the plantar aspect (e.g. heel) of the foot of a user contacts the distal surface 115 of the sensor assembly 110 and a downward force is applied by the weight of the user, the spring 140 is compressed by x and the applied force F on the heel by the sensor assembly is equal to kAx. FIG. 8F illustrates a state in which the force applied by the user has generated sufficient compression of the spring 140 such that the distal surface 115 of the sensor assembly is level with the top surface 102 of the platform.

As shown in FIG. 8F, a recess 148 may be provided in the proximal side of the sensor assembly 110 permit travel of the sensor assembly 110 without interruption from the screw 148. A recess may additionally or alternatively be included in the proximal side of the sensor assembly 110 to receive and secure the distal end of the spring 140.

The spring constant of the spring 140 may be selected such that when a subject applies their weight such that the sensor assembly 110 is fully compressed and the distal surface 115 of the sensor assembly 110 is flush with the top surface 102 of the platform, the pressure applied by the sensor assembly (due to the spring force) is equal to approximately 150 mmHg.

As shown in FIG. 8G, the longitudinal position of the nut 144 along the screw 146 may be actively varied (e.g. via a motor mechanically engaged with the nut 144), thereby varying (increasing or decreasing) the compression of the spring 140 and varying the resulting force that is applied to the plantar aspect and detected by the pressure sensor of the sensor assembly 110. The nut may start at an initial “home” position resulting in a compression of the spring and a resulting applied pressure onto the plantar foot equal to approximately 150 mmHg. From here, the compression of the spring may be increased or decreased by changing the longitudinal position of the nut along the screw and relative to the “home” position to vary the applied pressure on the plantar foot. As in the example embodiment illustrated in FIG. 8D, the tissue region that is probed by contact with the sensor assembly 110 does not change as the variable pressure is applied, thereby providing a robust and reliable measure of blood pressure. The constancy of the surface area of the distal surface 115, and the ability to maintain a constant contact area between the distal surface 115, may be facilitated by a sensor assembly having a rigid distal contact surface.

The inventors have found that the addition of compliance to the sensor assembly can dampen oscillations in PPG signal and pressure measurements which occur due to small fluctuations in weight applied to the assembly (e.g. from postural swaying). A compliant system is also considerably more comfortable for the user than a rigid system.

It will be understood that the embodiment illustrated in FIGS. 8E and 8F provides but one example implementation of a device having an integrated compliant mechanism and that other types and/or configurations of compliant mechanisms may be employed in the alternative. For example, which the figures illustrate this nut can be driven by a rotary actuator. Alternatively, the screw could be replaced with a rod and the nut/plate actuated by a linear actuator. In some instances, the spring could be replaced with compliant material such as foam. Alternatively, the screw and spring could be replaced with a pneumatic chamber (e.g. cylinder). In this case, compressed air provides cushioning and changing air pressure could result in changes in applied pressure on the plantar foot. An example implementation of such an embodiment is illustrated in FIG. 8H in which the sensor assembly is mechanically coupled to a piston 510 that is received within a cylinder 550. Compressed air is delivered to an inlet 520 of the cylinder (e.g. via connection to a pump) to apply pressure to the piston 550, which in turn results in the application of pressure to the surface region of the plantar aspect of the foot by the distal contact surface 115 of the sensor assembly 110. A distal region of the cylinder 500 is in fluid communication with the atmosphere, e.g. through the vent 530.

While the preceding example embodiment illustrated the incorporation of a compliant mechanism in the context of an active device in which the pressure applied by the sensor assembly to the plantar aspect is varied via motorized control, a compliant mechanism may be integrated into a passive device in which the user is responsible for varying the pressure applied to the sensor assembly by shifting their weight. An example implementation of such an embodiment is illustrated in FIGS. 8I and 8J. In FIG. 8I, the distal contact surface 115 of the sensor assembly 110 is shown biased beyond the upper surface of the platform 120 prior to the application of a force by the foot and the distal extension of the distal contact surface 115 may optionally be fixed by a structural stop (e.g. stop 150). The sensor assembly 110 is shown residing on a spring 140, which in turn rests on a fixed stop 550 (e.g. a plate) that is rigidly supported relative to the platform 102. The spring may optionally be centered around a shaft 560 that is absent of contact with the sensor assembly 110. In such example embodiment, the application of varying weight onto the sensor assembly results in a varying compression of the spring and resulting changes in the applied pressure on the plantar foot, as illustrated in FIG. 8J.

In some example implementations, one or more measures such as, but not limited to, one or more of user’s weight, the measured applied pressure, and the measured blood volume or flow waveform may be processed to control the offset of the distal surface of the sensor assembly in order to obtain a suitable waveform. For example, in example methods involving oscillometric processing, the measured plethysmographic waveform may be processed while varying the offset of the distal surface, or after varying the offset of the distal surface, to identify the presence or absence of one or more features corresponding to the MAP. If such features are absent from the measured plethysmographic waveform, the offset of the distal surface may continue or may be repeated. In another example embodiment, a target applied pressure that is expected to correspond to the MAP at the plantar aspect (, MAPfoot ) may be computed for a user (e.g. based on a typical MAPheart and an estimated height of the user) and the offset of the distal surface may be controlled such that the measured applied pressure range includes the target applied pressure. The offset translation rate may be controlled, for example, such that a rate of change of pressure is less than 6 mm Hg/s. In another example implementation, the offset translation rate may be controlled such that a rate of change of pressure is less than 6 mm Hg/s for pressures ranging between 90% and 110% of the mean arterial pressure. In example embodiments involving the direct measurement of SBP and DBP via arterial occlusion, the offset of the distal surface may be controlled such that the applied pressure range includes the SBP and the DBP.

Referring again to FIG. 1 , while the example device shown 1 is configured to accommodate the placement of both feet of a user, it will be understood that in other alternative example embodiments, the device may be configured to accommodate only a single foot of a user. For example, an alternative device configuration may involve a platform that has a surface area that would only accommodate a single foot, or a platform that has guidance markings only for assisting the placement of one foot.

In other example embodiments, the platform may include multiple sensor assemblies. In one example implementation, the platform may include two assemblies that are supported such that a first sensor assembly contacts the plantar aspect of one foot and the second sensor assembly contacts the plantar aspect of the other foot when both feet of a user a supported by the platform. In another example embodiment, the device may include an array of sensors.

As shown in FIG. 1 , the device may include indicator markings that assist the user with placement of the feet such that the plantar aspect of one of the feet is placed in a pre-selected configuration relative to the sensor assembly (e.g. such that the sensor assembly is located proximal to a selected artery when the user places their foot in a prescribed orientation on the platform). Such indicator markings may be fixed (e.g. defined by an outline shown on the upper surface of the platform).

Alternatively, the indicator markings may be reconfigurable to accommodate different foot sizes and/or the targeting of different arteries (or regions of a given artery) on the plantar aspect. In one implementation, a set of template sheets may be provided, where each template sheet can be placed on the top surface of the platform and aligned relative to the top surface of the platform. One or more template sheets may include a cut-out (aperture) corresponding to the location of the sensor assembly. A given template sheet may be aligned via alignment markings or via alignment of one or more edges of the template with one or more respective edges of the top surface of the platform (or, for example, alignment of the cut out relative to the sensor assembly). A suitable template sheet may be selected by a user from the set of template sheets, with each template sheet corresponding to a different foot size (where the user would select an appropriate template that best matches the user’s foot size). Additionally or alternatively, two or more template sheets may correspond to different orientations of a foot of a given foot size relative to the sensor assembly, where each orientation targets a different artery or location along a given artery of the plantar aspect.

Alternatively, in order to improve the precision and accuracy of plantar-based blood pressure measurements, one or more active device elements may be employed to assist with the placement of the foot relative to the sensor assembly (e.g. with the sensor assembly located directly below the plantar artery of interest). For example, the platform may include a plurality of display elements such as, but not limited to, a liquid crystal array or a set of light emitting diodes (e.g. a sparse array of light emitting diodes or a dense light emitting diode display array), which can be selectively activated to indicate a preferred foot placement relative to the sensor array. For example, the display elements may be selectively activated to indicate a preferred foot position and orientation based on, for example, one or more of a given foot size (e.g. selected as per input from a user) and a given target artery or arterial region. In other example implementations, one or more of the active device elements may be haptic, such as an array of pins, where each pin can be selectively raised relative to the upper surface of the platform to define an outline of the foot.

In some example embodiments, guidance may be provided to facilitate the placement of the foot of a user on the platform such that the current placement corresponds to a foot placement that was employed during a previous blood pressure measurement, which may be beneficial in providing repeated blood pressure measurements with improved accuracy. A measure of the previous foot placement may be obtained, for example, via a sensor array such as, but not limited to, a capacitive, resistive, optical, piezoelectric, or mechanical sensor array (for example, a mechanical sensor array may be provided by a discrete array of displaceable pins, with displacement of a given pin being detectable via a corresponding sensing circuit, e.g. through electrical contact). A sensor array may be provided proximal to or formed with the top layer of the upper surface of the platform. The sensor array may also be employed to perform blood volume or flow measurements and/or pressure measurements.

The sensor array is employed, when the previous blood pressure measurement is performed, to obtain a measure (e.g. scan) of the position of the plantar aspect of the foot. The scan may be stored on the device (and/or remotely stored) and can be subsequently employed to provide guidance to assist the user in positioning their foot in the same orientation as the previous measurement. For example, the scan may be processed to estimate an outer boundary of the foot and this outer boundary may be displayed or otherwise indicated, via an array of active device elements, as described above.

An example of such an embodiment is illustrated in FIG. 9, which schematically illustrates a platform 100 having an integrated sensor array and display array 300 (e.g. a capacitive touchscreen) capable of detecting the foot position and displaying an outline of the foot 310 or other suitable guidance to assist with foot placement for aligning a target region of the plantar aspect 50 with the distal surface 115 of the sensor assembly. As shown in the figure, an aperture may be formed in the sensor array and/or display element array to house the sensor assembly such that the distal surface is unimpeded (this configuration may be beneficial in example embodiments that involve motion of the sensor assembly relative to the upper surface of the platform 100). Alternatively, one or more of the sensor array and/or display element array may be formed over the sensor assembly (e.g. in example embodiments involving a sensor assembly that is static during blood volume or blood flow measurement), or, as noted above, the sensor array may itself be employed for performing blood volume/flow or pressure measurements.

In some example embodiments, the previous scan may be compared with a current scan to provide guidance to the user. The user may contact the plantar aspect of their foot with the platform and the sensor array may be employed to obtain a current scan. The current scan can then be compared to the previous scan to determine a relative position therebetween, and the relative position can be employed to provide instructions to the user (e.g. visual instructions provided on the display or auditory instructions) of the direction(s) in which the foot should be moved in order to achieve the previous foot orientation (this process can be repeated over multiple iterations to provide intermitted or continuous guidance to the user).

Referring now to FIG. 10, a system for performing plantar-based blood pressure measurements is schematically illustrated. The example system includes a platform 100 that supports a sensor assembly 110. As shown in the figure the sensor assembly may include a blood volume or blood flow sensor 120 and a pressure sensor 130 or may alternatively include a single sensor configured for measuring both the waveform and an applied pressure. The platform 100 may also house a drive mechanism 455, for example, as described above for varying a tilt of the platform or for controlling an offset of the distal surface of the sensor assembly 110 relative to the upper surface of the platform 100. The platform may also include a sensing mechanism for sensing a position and orientation of a user’s foot, such as a sensor array as described above. The platform may also include a display 170 for displaying, for example, instructions to a user to be followed when performing a blood pressure measurement, such as a maneuver involving the shifting of the body weight of the user (the display 170 may encompass part a subset or entirety of the surface area of the platform).

The platform 100 is are operatively coupled to control and processing circuity 400. As shown in the example embodiment illustrated in FIG. 10, the control and processing circuitry 400 may include a processor 410, a memory 415, a system bus 405, one or more input/output devices 420, and a plurality of optional additional devices such as communications interface 435, external storage 430, data acquisition interface 440 and a power supply 160. The example methods described above can be implemented via processor 410 and/or memory 415. As shown in FIG. 10, executable instructions represented as blood pressure calculation module 480, guidance module 485 and drive control module 490 are processed by control and processing circuitry 400 to execute instructions for performing one or more of the methods described in the present disclosure, or variations thereof. Such executable instructions may be stored, for example, in the memory 415 and/or other internal storage.

The methods described herein can be partially implemented via hardware logic in processor 410 and partially using the instructions stored in memory 415. Some embodiments may be implemented using processor 410 without additional instructions stored in memory 415. Some embodiments are implemented using the instructions stored in memory 415 for execution by one or more microprocessors. Thus, the disclosure is not limited to a specific configuration of hardware and/or software.

It is to be understood that the example system shown in the figure is not intended to be limited to the components that may be employed in a given implementation. For example, the system may include one or more additional processors. Furthermore, one or more components of control and processing circuitry 400 may be provided as an external component that is interfaced to a processing device. Furthermore, although the bus 405 is depicted as a single connection between all of the components, it will be appreciated that the bus 405 may represent one or more circuits, devices or communication channels which link two or more of the components. For example, the bus 405 may include a motherboard. The control and processing circuitry 400 may include many more or less components than those shown. In some example implementations, some aspects of the example methods described herein, such as the processing of the measured signals to calculate one or more blood pressure measures, may be performed via one or more additional computing devices or systems, such as a mobile computing device connected via a local wireless network (such as Wi-Fi or Bluetooth), and/or a remote server connected over a wide area network.

Some aspects of the present disclosure can be embodied, at least in part, in software, which, when executed on a computing system, transforms an otherwise generic computing system into a specialty-purpose computing system that is capable of performing the methods disclosed herein, or variations thereof. That is, the techniques can be carried out in a computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as ROM, volatile RAM, non-volatile memory, cache, magnetic and optical disks, or a remote storage device. Further, the instructions can be downloaded into a computing device over a data network in a form of compiled and linked version. Alternatively, the logic to perform the processes as discussed above could be implemented in additional computer and/or machine- readable media, such as discrete hardware components as large-scale integrated circuits (LSI's), application-specific integrated circuits (ASIC's), or firmware such as electrically erasable programmable read-only memory (EEPROM's) and field- programmable gate arrays (FPGAs).

A computer readable storage medium can be used to store software and data which when executed by a data processing system causes the system to perform various methods. The executable software and data may be stored in various places including for example ROM, volatile RAM, nonvolatile memory and/or cache. Portions of this software and/or data may be stored in any one of these storage devices. As used herein, the phrases “computer readable material” and “computer readable storage medium” refers to all computer-readable media, except for a transitory propagating signal perse.

Although many of the example embodiments described above refer to the detection of one or more blood pressure measures, it will be understood that the methods and devices disclosed herein may be employed to measure and record other biometric data, including, but not limited to, a heart rate, weight, step count, and standing time. Such biometric data may be stored on the device and/or transmitted to another device, optionally transmitted to a remote server for analysis and display on a user interface (e.g. a web-based or app-based user interface). The blood pressure measurements generated by the device may be optionally employed, for example, to calibrate blood pressure measurements made using another device, or vice versa.

Furthermore, although the preceding example embodiment have been described in association with a platform, it will be understood that the platform may be provided by a wide range of weight-bearing articles, including, but not limited to, a weight scale, a mat, a floor tile, a tablet, a shoe, and a shoe insert. In other example embodiments, the sensor assembly may be integrated into a wearable device such as a sock or sleeve.

The following examples are presented to enable those skilled in the art to understand and to practice embodiments of the present disclosure. They should not be considered as a limitation on the scope of the disclosure, but merely as being illustrative and representative thereof.

EXAMPLES

FIGS. 11A-11C plot experimental data demonstrating the measurement of blood pressure from the lateral plantar artery using a derivative-based algorithm. A prototype consisting of a platform and sensor assembly was used. The head of the sensor assembly consisted of a 3.5 cm diameter circular plastic disc with infrared light emitting diode and photodiode sensor embedded within it and separated by 1 cm. The head of the assembly was fixed rigidly ~3 mm off the surface of the platform. Force applied onto the sensor assembly was measured using a load cell. The subject was normotensive, weighed 77 kg with an h (height of the heart relative to the foot) of 1.4 m. With both feet on the platform, and the right foot on the sensor assembly, weight was gradually shifted onto the sensor assembly in a manner similar to FIG. 6C.

FIG. 11 A plots the applied pressure on the lateral plantar artery versus time. The corresponding PPG signal versus time, plotted in FIG. 11 B, shows an initial increase in amplitude of the PPG signal amplitude followed by decrease. The amplitude, namely the difference between the maximum and minimum PPG signal (DO), as derived from FIG. 11B, versus applied pressure derived from FIG. 11A, is shown in FIG. 11 C fitted with a 7 ^th order polynomial. The maximum amplitude occurs when the applied pressure equals the MAP, which was determined to be 211 mmHg. According to the present example derivative-based method, the DBP corresponds to the pressure at the maximal of dA/dP (the maximum slope of the plot of amplitude vs P), which was found to be 195 mmHg, and the SBP corresponds to the pressure at the minimum of dA/dP (the minimum slope of the plot of amplitude vs P), which was found to be 226 mmHg. Correcting for hydrostatic pressure (113 mmHg), the calculated MAP, DBP and SBP were 98 mmHg, 82 mmHg and 113 mmHg, respectively.

The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.