FIELD OF THE INVENTION

The present invention relates to a monitoring apparatus for monitoring vital sign information of a subject, in particular for hemodynamic monitoring of a subject. The present invention further relates to a monitoring method for monitoring vital sign information of a subject and to a computer program product comprising computer readable program code means embodied therein for causing a computer to carry out the steps of the monitoring method for monitoring the vital sign information of the subject.

BACKGROUND OF THE INVENTION

Hemodynamic monitoring to determine hypervolemia or hypovolemia is important measurement of vital signs of a patient in the intensive care and during major surgeries. The functional hemodynamic monitoring can be defined as the assessment of the dynamic interactions of hemodynamic variables in response to a defined perturbation.

In general, the hemodynamic monitoring can be performed invasively e.g. by an arterial line or indirect by means of pulse signal contour analysis.

Commonly, the hemodynamic monitoring and the monitoring of the patient's blood volume status is performed by measuring a beat-to-beat stroke volume variation or by measuring a pulse pressure variation, wherein hand-held ultrasound probes are used to measure the respective signal e.g. at the carotid artery and using Doppler measurements. A corresponding method for measuring a blood volume based on esophageal Doppler measurements is e.g. known from "Monitoring of respiratory variations of aortic blood flow velocity using esophageal Doppler" in Intensive Care Med, 2004, vol. 30, pp. 1182 - 1187.

The disadvantage of the known hemodynamic monitoring methods is that they are either invasive and, therefore, obstructive and uncomfortable for the use or require an ultrasound imaging system having a large technical effort and an increased handling effort and needs a large experience of the user to measure the respective signal with high reliability. SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved monitoring apparatus for monitoring vital sign information of a subject with low technical effort and with a high reliability.

According to one aspect of the present invention, a monitoring apparatus for monitoring vital sign information of a subject is provided comprising:

a transducer for emitting and receiving ultrasound waves, light waves, or electromagnetic waves and for providing a variable measurement signal on the basis of the ultrasound waves, the light waves, or the electromagnetic waves received from the subject, a processing unit for determining a first periodical signal component of the variable measurement signal and a second periodical signal component of the variable measurement signal, wherein the processing unit is adapted to determine the vital sign information on the basis of the first periodical signal component and to determine a signal quality of the variable measurement signal on the basis of the second periodical signal component.

According to another aspect of the present invention, a monitoring method for monitoring vital sign information of a subject is provided comprising the steps of:

determining a variable measurement signal on the basis of ultrasound waves, light waves, or electromagnetic waves received from the subject,

determining a first periodical signal component of the variable measurement signal and a second periodical signal component of the variable measurement signal, and determining the vital sign information on the basis of the first periodical signal component and determining a signal quality of the variable measurement signal on the basis of the second periodical signal component.

According to still another aspect of the present invention, a computer program product comprising computer readable program code means embodied therein is provided for causing a computer to carry out the steps of the monitoring method according to the present invention, when said computer program is carried out on a suitable computer or processor.

Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed method has similar and/or identical preferred

embodiments as the claimed device and as defined in the dependent claims.

The present invention is based on the idea to determine the vital sign information on the basis of a variable measurement signal, i.e. a variable ultrasound signal, a variable light signal, or a variable electromagnetic wave signal, which is determined by means of an ultrasound transducer or a light emitter and light detector or an electromagnetic wave emitter and detector at a volume of the subject, wherein a first periodical signal component of the variable measurement signal is extracted from the measurement signal and utilized to determine the vital sign information and wherein a second periodical signal component is derived from the ultrasound signal, the light signal or the electromagnetic wave signal and utilized to determine a signal quality of the variable measurement signal. Since the vital sign formation, which is at least partially a respiration-induced vital sign or corresponds at least partially to a respiration-induced vital sign is determined on the basis of the measurement signal, a non-invasive measurement can be provided and since the signal quality is determined on the basis of the second periodical signal component derived from the measurement signal, the respective signal quality and the respective position of the transducer can be determined with high precision so that a reliable monitoring of the vital sign can be provided. Since the signal quality is not determined on the basis of the signal strength of the received signal itself, but on the basis of the second periodical signal component of the variable measurement signal, the variable measurement signal can be easily distinguished from different vital signals of the subject and the measurement of artefacts and noise can be avoided. Since the signal quality can be determined with high precision on the basis of the second periodical signal component, a simple transducer can be utilized while mismeasurements can be avoided so that the overall technical effort for the monitoring apparatus can be reduced.

Consequently, the present invention provides a monitoring of a vital sign information of a subject with an improved reliability and with a reduced technical effort.

In an embodiment, the first periodical signal component is an upper modulation component and the second periodical signal component is a lower modulation component of the variable measurement signal. This is a possibility to precisely distinguish the vital sign information detection in the variable measurement signal and the detection of the signal quality with low technical effort.

In an embodiment, the processing unit is further adapted to determine the vital information on the basis of the first periodical signal component and on the basis of the second periodical signal component. This is a possibility to further improve the preciseness of the detection of the vital sign information of the subject on the basis of the variable measurement signal.

In an embodiment, the processing unit is further adapted to determine a ratio of the first periodical signal component and the second periodical signal component and to determine the vital sign information on the basis of the ratio of the first periodical signal component and the second periodical signal component. This is a possibility to determine the vital sign information, in particular any hemodynamic signal like a volume status of the subject with low technical effort and to distinguish different levels of the vital sign formation.

In an embodiment, the processing unit is further adapted to determine an upper amplitude of the variable measurement signal on the basis of the first periodical signal component and a lower amplitude of the variable measurement signal on the basis of the second periodical signal component, and to determine the vital sign information on the basis of a ratio of the upper and the lower amplitude. This is a possibility to precisely determine an upper modulation and a lower modulation of the variable measurement signal and to determine in particular a hemodynamic status like the blood volume status of the subject on the basis of the so determined upper amplitude and lower amplitude.

In an embodiment, the transducer is an ultrasound transducer including at least one ultrasound transducer element for emitting and receiving ultrasound waves and for providing a variable ultrasound signal as the variable measurement signal on the basis of the ultrasound waves received from a volume of the subject. This is a possibility to provide an ultrasound measurement with low technical effort.

In an alternative embodiment, the transducer is a light transducer including at least one light emitter and a light detector for emitting and receiving light waves and for providing the variable measurement signal on the basis of the light waves received from the volume of the subject and detected by the light detector. This is a possibility to provide an unobtrusive and contactless vital sign measurement with low technical effort. In an embodiment, the light emitter comprises a laser emitter for emitting the light. This is a possibility to detect a photoplethysmography signal from the subject and to determine the vital sign information on the basis of the photoplethysmography signal.

In an alternative embodiment, the transducer is an electromagnetic transducer including an emitter and a detector for transmitting and receiving electromagnetic waves. This is an alternative possibility to detect the vital sign information with high precision.

In an embodiment, the vital sign information is a hemodynamic signal of the subject, in particular a blood volume status of the subject. This is a possibility to determine hemodynamics of the subject and to distinguish hypervolemia, normovolemia and

hypovolemia non-invasively with reduced effort.

In an embodiment, the ultrasound transducer is a wide angle continuous wave Doppler ultrasound transducer. This is a possibility to reduce the technical effort for providing the variable ultrasound signal and for monitoring the vital sign information of the subject in general.

In an embodiment, the ultrasound signal is a blood velocity signal determined in the volume of the subject. This is a possibility to determine the blood volume status or the blood pressure of the subject non-invasively with low technical effort.

In an embodiment, the ultrasound transducer comprises a single transducer element for emitting and receiving the ultrasound waves.

In an embodiment, the ultrasound transducer comprises an array of transducer elements and a control unit for controlling the array of transducer elements, wherein the control unit is adapted to steer a field of view of the array of transducer elements towards the volume of interest. This is a possibility to improve the detection of the variable ultrasound signal and to improve the preciseness of the monitoring of the vital sign formation of the subject, since the volume of interest can be selected automatically by means of the control unit.

In an embodiment, the control unit is adapted to steer the field of view towards the volume of interest on the basis of the variable ultrasound signal. This is a possibility to steer the field of view towards the largest signal strength of the variable ultrasound signal, so that the preciseness of the monitoring of the vital sign information can be further improved.

In an embodiment, the ultrasound transducer comprises an array of transducer elements which provide a static electromagnetic beam transmission.

In an embodiment, the processing unit comprises an analysis unit for analyzing the variable measurement signal and at least two diodes connecting the analysis unit to the transducer for filtering the variable measurement signal received from the transducer. This is a possibility to determine the first periodical signal component and the second periodical signal component of the variable measurement signal.

In a preferred embodiment, the at least two diodes are disposed anti-parallel to each other. In other words, the diodes are connected in parallel to each other having opposite forward directions. This is a possibility to determine the first periodical signal component and the second periodical signal component as positive and negative signal components with low technical effort.

In a preferred embodiment, the processing unit comprises an offset unit for providing an offset signal to the variable measurement signal. This is a possibility to set a zero point or a zero level of the variable measurement signal to a desired level so that the first periodical signal component and the second periodical signal component can be easily determined as positive and negative signal component of the variable measurement signal.

In a further embodiment, the transducer is coupled to a coupling layer for coupling the transducer to the subject. This is a possibility to connect the transducer to the subject with low technical effort and to precisely determine the variable measurement signal and the corresponding vital sign information continuously.

In a further preferred embodiment, the ultrasound transducer is coupled to the subject by means of an adhesive layer. This is a possibility to attach the ultrasound transducer fixedly to the subject to determine the vital sign information precisely and continuously over a large time period.

In an embodiment, the ultrasound transducer comprises a string of transducer elements, and wherein the ultrasound signal is selected from a plurality of ultrasound signals received by the transducer elements. This is a possibility to determine one of the transducer elements, which is in the vicinity of a blood vessel to be measured so that the variable ultrasound signal can be determined with low technical effort.

In a preferred embodiment, the ultrasound signal is selected from the plurality of ultrasound signals received from the transducer elements having the largest signal strength. This is a possibility to select the variable ultrasound signal having the best signal quality so that the vital sign information can be determined precisely with low technical effort.

As mentioned above, the vital sign information, in particular the blood volume status or the blood pressure can be determined on the basis of the first periodical signal component of the variable measurement signal and the signal quality can be determined based on a separate second periodical signal component of the variable measurement signal so that a simple transducer can be utilized while the precision of the determination of the vital sign information can still be achieved. Hence, the vital sign information of the subject can be determined with high precision and low technical effort in general.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

Fig. 1 shows a schematic representation of a monitoring apparatus in use to scan a volume of a patient's body; Fig. 2a - c show different timing diagrams of blood velocities and the corresponding airway pressure measured at a vessel of the patient;

Fig. 3 shows a schematic flow diagram of a method to determine the vital sign information of the patient;

Fig. 4 shows a schematic representation of a control unit and a processing unit for determining the vital sign information of the subject on the basis of a variable ultrasound signal; and

Fig. 5 shows a schematic representation of an ultrasound transducer including a string of transducer elements for determining an ultrasound signal of the patient's body.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a schematic illustration of a monitoring apparatus generally denoted by 10. The monitoring apparatus 10 is provided for monitoring vital sign information of a subject 12, in particular a patient 12. The monitoring apparatus 10 comprises an ultrasound transducer 14 including one transducer element or a multitude of transducer elements for transmitting and receiving ultrasound waves. The ultrasound transducer 14 is preferably attached to the patient's body by means of an adhesive layer 16 and attached to the skin of the patient's body in the vicinity of a large artery 18 such as the carotid as shown in Fig. 1 or the aorta. The ultrasound transducer 14 is attached to the subject 12 to measure non- invasively a variation of a blood velocity in the artery 18 and to calculate the blood pressure and/or the blood volume status of the subject 12 on the basis of the variation of the blood velocity as described in the following. The ultrasound transducer 14 including the single transducer element is preferably formed as a simple wide-angle continuous-wave Doppler system in order to measure the blood velocity in the artery 18. In an alternative embodiment an ultrasound transducer 14 comprises the multitude of transducer elements which are arranged in a string of transducer elements or in a 2D-transducer array to determine the blood velocity on the basis of a wide-angle continuous-wave Doppler measurement. The transducer elements may be formed as piezoelectric micro-machined ultrasound transducer (PMUT) or as capacitive micro-machined ultrasound transducers (CMUT).

The monitoring apparatus 10 further comprises a control unit 20 including a controller 22 and a processing unit 24. The control unit 20 is connected or connectable to the ultrasound transducer 14 by means of a cable connection or by means of a wireless connection, wherein the controller 22 receives a variable ultrasound signal as measurement signals from the ultrasound transducer 14 and controls the ultrasound transducer 14 accordingly. The processing unit 24 receives the variable ultrasound signal from the ultrasound transducer 14 and determines a first periodical signal component of the variable ultrasound signal and a second periodical signal component of the ultrasound signal and determines the vital sign information of the subject 12 on the basis of the first periodical signal component and in particular on the basis of the second periodical signal component as described in the following. The processing unit 24 may further determine a signal quality of the variable ultrasound signal on the basis of the second periodical signal component.

The control unit 20 may be connected or connectable to an output device 26, e.g. a display device 26 and may be connected or connectable to an input device 28 which may be connected to the output device 26 or to the control unit 20 in order to control the acquisition of the measurement data. The output device 26 and the input device 28 may be connected to the control unit 20 by means of a cable connection or by means of a wireless connection.

The ultrasound transducer 14 is attached to a skin of the subject 12 and formed e.g. as a wearable patch or a sticky plaster which is placed on the top of the skin at the artery 18 as shown in Fig. 1. The ultrasound transducer 14 measures the blood velocity in the artery 18 on the basis of the ultrasound waves received by the ultrasound transducer 14 and the ultrasound transducer 14 provides the corresponding variable ultrasound signal to the processing unit 24.

The processing unit 24 determines a first periodical signal component of the variable ultrasound signal as an upper modulation component or an upper amplitude of the variable ultrasound signal and determines the vital sign information, which may be any hemodynamic signal like a blood pressure or a blood volume status of the subject on the basis of the so determined first periodical signal component. The vital sign information may be at least partially a respiration-induced vital sign and corresponds at least partially to the respiration of the subject 12. The processing unit 24 further determines a second periodical signal component as a lower modulation component or a lower amplitude of the variable ultrasound signal and determines a signal quality of the variable ultrasound signal on the basis of this second periodical signal component. The processing unit 24 can determine noise or movement artifacts affecting the whole variable ultrasound signal and can distinguish those noise or artifact signals from the vital sign information and in particular from the onesided hemodynamic modulation of the variable ultrasound signal. Hence, the ultrasound transducer 14 can be formed as a simple ultrasound transducer for determining a vital sign information of the subject 12, since the quality of the detected signal is evaluated on the basis of the second periodical signal component. If the measurement of the second periodical signal component shows that the variable ultrasound signal is corrupted or an artifact signal, the measurement of the variable ultrasound signal is ignored and a warning signal may be provided by means of the output device 26 to the user.

In an alternative embodiment, in which the ultrasound transducer 14 comprises the 2D-transducer array, the control unit 22 is adapted to steer the ultrasound waves automatically towards a volume of the subject, where the variable ultrasound signal is measured having the largest signal strength. This is a possibility to steer the ultrasound waves automatically to the artery 18 and to provide a precise and reliable variable ultrasound signal to the control unit 20.

In a further embodiment, the ultrasound transducer 14 comprises a string of transducer elements which are arranged in a straight line, wherein the string of transducer elements is attached to the subject 12 so that the string of the transducer elements is arranged across to the artery 18. Each of the transducer elements provide a separate variable ultrasound signal and the controller 22 selects the variable ultrasound signal from the transducer elements having the best signal quality and/or the largest signal strength.

To determine the vital sign information and in particular the blood volume status, the processing unit 24 calculates a first ratio of the lower amplitude of the variable ultrasound signal to the average value of the variable ultrasound signal and a second ratio of the upper amplitude to the average of the variable ultrasound signal. The processing unit 24 further determines a ratio between the first and the second ratio, i.e. the upper amplitude modulation and the lower amplitude modulation and determines the volume status or the fluid responsiveness of the patient 12 on the basis of the so determined ratio. The ratio may be evaluated on the basis of a linear or a non-linear function or a look-up table, wherein a low value of the ratio reflects hypovolemia and a high value reflects hypervolemia, i.e. fluid overload.

In an alternative embodiment, the monitoring apparatus 10 comprises a light source, in particular a laser light source such as a laser speckle or a laser Doppler imaging unit which are sensitive to the movement of the artery 18 and other superficial tissues like organs exposed during surgery. The blood velocity in the artery 18 is measured on the basis of a light signal emitted by the light source and detected by a light detection element and the light detection element provides a variable measurement signal on the basis of the detected light. The variable measurement signal is evaluated identical with the evaluation of the variable ultrasound signal as mentioned above. In an embodiment, the detected light may be used for detecting a photoplethysmography (PPG) signal.

In an alternative embodiment, the monitoring apparatus 10 comprises a transducer for emitting and receiving electromagnetic waves, wherein the transducer provides a variable measurement signal corresponding to vital sign information of the subject 12 on the basis of the detected electromagnetic waves. The variable measurement signal is evaluated identical with the evaluation of the variable ultrasound signal as mentioned above.

According to a further embodiment, the respiration of the subject 12 can be determined separately e.g. by means of a ventilator, an accelerometer or a respiration belt and the respiration signal can be utilized to demodulate the variable measurement signal, i.e. the Doppler signal. This can be advantageous if the variable measurement signal has a reduced signal quality.

Fig. 2a-c show timing diagrams of a blood velocity and an airway pressure for three different blood volumes, wherein Fig. 2a shows the respective measurements for hypervolemia, Fig. 2b shows the measurements for normovolemia and Fig. 2c shows the respective diagrams for hypovolemia.

The measured blood velocity v which corresponds to the variable ultrasound signal determined by the ultrasound transducer 14 or the light detection device is a periodical signal, which shows an upper amplitude modulation (systolic) and a lower amplitude modulation (diastolic), wherein the upper peaks of the measured blood velocity, i.e. the upper amplitude of the measured blood velocity varies periodically over time. The upper amplitude is a difference between the positive peaks and an average signal component of the ultrasound signal. The modulation of the blood velocity is a respiration induced variation. The amplitude variation of the blood velocity increases from Fig. 2a to Fig. 2c. Further, the signal of the measured blood velocity v shows a lower amplitude modulation, wherein the lower peaks of the blood velocity signal vary periodically. The lower amplitude is a difference between the negative peaks and an average signal component of the ultrasound signal. The lower amplitude variation is low for the different blood volumes and varies slightly from Fig. 2a to Fig. 2c. From the upper amplitude modulation of the blood velocity v, the airway pressure P can be determined as shown in Fig. 2a-c.

On the basis of the lower amplitude modulation of the blood velocity v, the signal quality of the measured blood velocity v can be determined and signal artifact or noise corrupting the measured blood velocity signal can be determined. Fig. 3 shows a schematic flow diagram of a method to determine the vital sign information of the subject 12 and in particular the blood volume status of the subject 12. The monitoring method shown in Fig. 3 is generally denoted by 30.

The measured value is in this particular case the blood velocity v but the measured value may be any hemodynamic signal that is modulated by the respiration at one side or at two sides.

The method 30 starts with step 32, the detection of the ultrasound, light or electromagnetic waves by means of the ultrasound transducer 14 or the light measurement device or an electromagnetic wave detector and the determining of the variable measurement signal. The variable measurement signal is evaluated at a step 34 and on the basis of the signal strength, the transducer array may be steered to the artery 18 and the measurement of the variable measurement signal is repeated as indicated by the feedback loop shown in Fig. 3.

In step 36, the first periodical signal component is determined as an upper modulation component or an upper amplitude modulation of the variable measurement signal and in step 38 the second periodical signal component is determined as a lower modulation component or a lower amplitude modulation of the variable measurement signal. The first periodical signal component and the second periodical signal component are evaluated at step 40 as mentioned above by determining a ratio between the respective amplitude values. At step 42, the second periodical signal component is evaluated in order to determine the signal quality of the variable measurement signal and to determine whether the variable

measurement is corrupted by artifacts or noise. At step 44, the vital sign information of the subject 12, e.g. the blood volume status is determined, wherein the respective measurement is ignored if a corruption of the variable measurement signal has been detected as step 42.

Hence, a reliable determination of the vital sign information and in particular the blood volume status of the subject 12 can be determined with low technical effort and high precision.

The determination of the vital sign information of the subject at step 44 may be calibrated on the basis of a parallel different measurement method of the respective vital sign information e.g. on the basis of an invasive measurement method. The calibration may be performed on different patients in order to determine an appropriate classification of the vital sign information (e.g. the volume status) and stored in a memory device for further measurements. Fig. 4 shows a schematic diagram of the control unit 20. The control unit 20 is connected to the ultrasound transducer 14 or the light detection unit and receives the corresponding variable measurement signal. The control unit 20 comprises a Doppler electronic unit 46, which evaluates the measurement and determines the variable

measurement signal corresponding to the blood velocity in the artery 18. The control unit 20 further comprises an analysis unit 48, which is connected via two diodes 50, 52 to the Doppler electronic unit 46 for filtering the variable measurement signal and for providing the first periodical signal component and the second periodical signal component of the variable measurement signal to the analysis unit 48. Since the first and the second periodical signal components are positive and negative peaks of the variable measurement signal, the diodes 50, 52 which are connected antiparallel to each other can filter the corresponding periodical signal components with low technical effort. The diodes 50, 52 are connected to each other at one side and in opposite forward directions. Alternatively, the analysis unit 48 may be connected via a digital circuit to the Doppler electronic unit 46 for filtering the variable measurement signal and for providing the first periodical signal component and the second periodical signal component of the variable measurement signal to the analysis unit 48. In that case, the digital circuit serves as a digital filter e.g. for providing the first periodical signal component and the second periodical signal component to the analysis unit if the signal components are positive or for yielding the ratio of the first and the second periodical signal component.

The analysis unit 48 determines a modulation of the upper amplitude and the lower amplitude of the variable measurement signal on the basis of the first and the second periodical signal component and compares the amplitude modulation to the average of the variable ultrasound signal which is also provided by means of a bypass line to the analysis unit 48. The analysis unit 48 may also receive an external reference signal to obtain the blood volume status of the subject 12 on the basis of corresponding functions or look-up tables.

The analysis unit 48 provides the vital sign information e.g. the blood volume status as an output signal to the output device 26.

Due to the antiparallel diodes 50, 52, the upper and the lower amplitude modulation can be easily determined, wherein an offset unit may provide a corresponding offset signal to the variable measurement signal so that the respective first and second periodical signal component can be easily distinguished as positive and negative signal component of the variable measurement signal. Fig. 5 shows an embodiment of the ultrasound transducer 14 comprising a plurality of ultrasound transducers 54, which are arranged in a straight line or a string as shown in Fig. 5. The string of transducer elements 54 is disposed across the artery 18 to be measured, wherein each of the transducer elements 54 provide a separate variable ultrasound signal to the control unit 20 (not shown). The control unit 20 and in particular the controller 22 select one of the variable ultrasound signals received from the ultrasound transducer elements 54 having the highest signal strength to determine the variable ultrasound signal having the best quality and the best placement with respect to the artery 18. In an alternative embodiment, the variable ultrasound signal of the plurality of signals received from the transducer elements 54 is selected on the basis of the second periodical signal component determined by the processing unit 24 so that in advance the variable ultrasound signal which is not corrupted by artifacts or noise can be selective.

The string of transducer elements 54 can therefore be placed easier with a reduced precision and is also more robust against displacement and movement e.g. of the skin of the subj ect with respect to the artery 18.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Any reference signs in the claims should not be construed as limiting the scope.