Related Applications This is a continuation-in-part of co-pending United States Patent Application Serial No. 780,398 filed on September 26, 1985 entitled "Continuous Cutaneous Blood Pressure Measuring Apparatus and Method, United States Patent Application Serial No. 858,713 filed on May 2, 1986 entitled "Apparatus for Measuring Blood Pressure", by Edward H. Hon, M.D. and Edward D. Hon, and United States Patent Application Serial No. 915,130, filed October 2, 1986 for "External Uterine Contraction Monitoring Device" by Edward H. Hon, M.D., Edward D. Hon and Robert W. Hon.

Background of the Invention This invention relates to an improved method and apparatus for continuously and non-invasively measuring cutaneous blood pressure patterns in an isolated portion of tissue. The physiological data thus obtained are related to , but not identical to, blood pressure measurements of central arterial circulation, such as those obtained with the convcentional auscultatory method of estimating brachial artery blood pressure. In particular, the invention finds use as part of a general system for the measurement of blood pressure based on'repetitive evaluation of the cutaneous blood pressure fluctuation patterns of minute branches of larger arteries and therefore reflects the arterial blood pressure of the general circulation. This is to be expected since the latter is the source of the former.

The method and apparatus of the present invention enables continuous monitoring of blood pressure patterns over extended periods of time. This is often needed in the evaluation of circulatory function and ambulatory monitoring of cardiac function, and is useful for hypertension studies and for obtaining records of circulation in the peripheral systems, particulary of the limbs, fingers and toes. In the past, various artery occlusion procedures have been used which cause a stopping or restriction of the blood flow in the radial, brachial, dorsalis, pedis.

temporal and other arteries to estimate blood pressure, particulary of the central circulatory systems. Data thus obtained are by their very nature discontinuous.

It has been possible to insert, temporarily, pressure sensing devices and/or catheters directly into the arteries of the circulatory system for direct continuous measurements (invasive method of measuring) . While intro-arterial catheterization may provide more precise measurements of blood pressure than arterial occlusion 0 devices, the pressure measured is likely to be more related to the central circulation than to the peripheral circulation. Also, the blood pressure measurements and patterns thus obtained are likely to be altered by the traumatic operation of inserting the catheter, by the drug 5 administered so that the catheter can be inserted, and by the presence of a foreign body in the circulatory system. Certainly, such an invasive system can not be used in ordinary circumstnces.

The principal non-invasive blood pressure measuring 0 technique in use today is an auscultatory system where a pressure is applied to occlude a major artery, such as the brachial artery. In practice, an inflatable encircling cuff is placed around the upper arm and inflated to occlude the major artery, e.g., brachial, to prevent flow of blood 5 in the artery. As the pressure in the cuff is slowly lowered, permitting flow of blood in the artery, Korotkoff sounds are heard. The cuff pressure at which the first sound is heard is defined as the systolic pressure. The pressure in the cuff is then lowered further permitting the 30 blood to flow freely through the artery. The pressure in the cuff at which the sound fades is defined as the diastolic pressure.

A second occluding cuff technique uses palpation of the pulse rather then auscultation. In this palpatory 35 system, as the occluding cuff pressure is slowly released, arterial pulsations are detected by palpation. The pressure level of the cuff at which the pulsations are first perceived is designated as systolic blood pressure. Diastolic blood pressure cannot be detected by palpation.

Another occluding cuff system uses the maximum and minimum oscillations of arterial blood pressure as reference to cuff pressure as indications of systolic and diastolic blood pressure, respectively. In addition to

5 being an intermittent, occlusive technique, the measurements thus obtained are likely influenced by the volume of the limb around which the cuff is applied.

It can be generally stated that all blood pressure measurements which are based upon arterial occlusion are

1.0 inherently discontinuous, needing to be repeated, at best, from time to time. Such measurements cannot resolve blood pressure patterns on a beat to beat basis, or show the wave form of the individual beats.

Thus, although the current method of auscultatory 15

15 measurement of brachial blood pressure is by far the most widely used technique for blood pressure measurement, the technique is relatively imprecise since the observed values vary from observer to observer and the very act of taking the blood pressure itself causes a momentary change in the 0 person's blood pressure. Additionally, since occlusion itself is known to have physiological and psychological effects, the measurements may be distorted.

A non-invasive, non-occlusive approach to the measurement of blood pressure would have many advantage. 5 Unfortunately, prior techniques for this purpose have been found to have disadvantage. Those directed at measuring arterial pressure by placing a transducer directly over a partially compressed radial or dorsalis pedis artery can, under optimum circumstances, provide accurate records for 0 short periods of time. However, the required counter pressure has to be maintained, e.g. with a pneumatic system, and considerable difficulty is experienced in maintaining constant mechanical coupling between the tissue overlying the artery and pressure on the arterial wall 5 during even the slightest patioent motion.

An example of this type of measuring system is disclosed in U.S. Patent No. 3,880,145 to E.F. Blick, issued April 29, 1975. Blick described a system using a strain gauge to flatten the radial artery at the inside of

the wrist. A second sensor is mounted cutaneously alongside, but off the artery. The signal from the second sensor is subtracted from the sensor associated with the flattened artery. In practice, the signal from the radial artery sensor contains arterial pulsations as well as "noise". The noise which is measured by the cutaneous transducer is subtracted from the former signal, leaving a measurement of the arterial pulsations alone. Such systems are complex and during patient movement it is very difficult to precisely match the "noise" component arising from both sensors.

In the patent to Iberall, U.S. Patent No. 3,704,708, and the Bigliano, U.S. Patent No. 3,123,068 the apparatus is placed over an artery and the blood pressure variations in the artery measured. There is no means for isolating the cutaneous tissue from the effects of the blood vessel. The Iberall device does not measure the changes in the pressure in the cutaneous tissue of a digit, such as a finger or toe, but only the direct changes in blood pressure of the artery. There is no literature suggesting that such apparatus, which is basically the same approach as that of Blick, would be capable of measuring such changes in the cutaneous tissue. Additional prior art is referred to in the co-pending applications. Elastic strain gauge techniques which encircle limbs or digits have also been used. In such devices, a finger or toe is encircled. Since the digit volume increases with arterial inflow and decreases with venous outflow, the change in volume can be measured and related to blood pressure. However, the system is at least partially occlusive in nature and decreases capillary blood flow. Hence, again, it can be used only intermittently since it causes distortion of the physiological data. It is also not possible to obtain continuous blood pressure records for hours at a time. Also, it is difficult to calibrate since it is temperature sensitive, and must be calibrated off the body part.

A general discussion and review of various previously proposed systems for blood pressure monitoring is given in

the book, "The Direct and Indirect Measurement of Blood Pressure", by L.A. Geddes (Year Book Medical Publishers, Chicago, 1970) where a number of blood pressure measuring techniques are outlined (see pages 37, 71, 87 and 96).

5 It is also desirable to provide an easily attached stable transducer support for easily and quickly attaching the device to the patient.

It has been demonstrated that there is a hitherto unfulfilled need for a sensitive, continuous, easily used

10 non-invasive, non-occlusive measuring technique for recording blood pressure measurements and beat to beat patterns undistorted and uninterrupted by the measuring system, per se. The method and the apparatus of the present invention enables non-invasive, non-occlusive

15 continuous measurements over extended period of time. Continuous information of this type is essential for adequate evaluation of cardiac and vascular function. It is of particular importance in the diagnosis and treatment of hypertension, since it provides detailed information 20 concerning the peripheral circulation not heretofore available.

SUMMARY OF THE INVENTION The apparatus of the present invention continuously measures cutaneous blood pressure with a pressure

25 transducer, such as a strain gauge (or similar pressure measuring device) maintained against a portion of the body, preferably on the fleshy part of the middle finger, or on a toe. The active surface of the pressure transducer is surrounded by a tissue isolating means and is fitted within

30 a housing which holds the pressure transducer against the ^' tissue at a constant pressure by means of a spring pressing against the top of the transducer.

A small portion of cutaneous tissue is isolated from the surrounding tissue by an isolation ring surrounding the

35 active surface of the transducer and pressing against the tissue. This isolation ring projects below the active measuring surface of the strain gauge and serves to isolate the tissues and reduce noise emanating from adjacent tissue. Further the isolation ring, which is larger than

the active surface of the pressure transducer, causes the portion of the cutaneous tissue to protrude into the opening formed by the isolation ring and the pressure transducer into the shape of a dome, rather than a flat 5 surface. The minute blood pressure pulsations in this protruding dome of isolated cutaneous tissue are measured with a pressure transducer, such as a strain gauge, whose active measuring surface is tangentially oriented to the dome of the isolated cutaneous tissue. 10 It has been found that having the diameter of the active surface of the transducer somewhat smaller than the diameter of the isolation ring provides more stable and sensitive measurements.

The magnitude of the recorded blood pressure changes 15 are affected not only by the change within the isolated cutaneous tissue, but also by the forces which are holding the isolation ring against the tissue. In order to keep these forces sufficiently constant, the strain gauge assembly must be attached to a stabilizing platform in a 20 substantially -rigid mechanical manner. '

The digit supporting member is a slightly tapered hollow tubular member having an opening at one end, and a perpendicular tubular transducer holding member proximate to the other end. The open end of the tapered tubular member 25 has a spring mechanism for altering the size of the opening. A cap, having a biasing spring, presses the transducer placed in the transducer holding member against the finger of the patient.

In practice, the initial pressure applied to the 30 cutaneous tissue may be adjusted so that the observed cutaneous blood pressure is a given number of mms Hg. below the brachial systolic blood pressure, if the latter is used as a reference point. Alternatively, a predetermined known coupling pressure may be applied to the non-active end of 35 the strain gauge assembly by mechanical means, such as a calibrated spring, by pneumatic means, or directly by a second strain gauge or other pressure sensing device. In situations where known coupling pressures are used, cutaneous blood pressure changes may be referenced to them,

as well as to the clinically determined brachial blood pressure. When the foregoing non-invasive, non-occlusive technique is used as described, it is possible to continuously make cutaneous blood pressure measurements and record patterns under most clinical circumstances even during strenuous exercise, such as exercising or running on a treadmill.

Object of the Invention It is an object of the present invention to provide apparatus for making blood pressure measurements which will overcome the disadvantages of the prior art.

A further object of the present invention is to provide a method and apparatus for obtaining blood pressure measurements which do not require immobility of the patient and which provide a continuous, non-invasive blood pressure measurement.

A further object of the present invention is,to provide a more sensitive blood pressure measurement system. It is further object of the present invention to provide a non-invasive, non-occlusive blood pressure evaluation technique that will provide permanent records of momentary changes in blood pressure, and make it possible to evaluate even the evanescent effects of mementary neurovascular reflexes. It is yet another object of the present invention to provide a system that is inexpensive to manufacture and easy to use in association with equipment presently widely used by physicians.

These and other objects and features of the invention will become apparent from the following description and claims when taken in conjection with the accompanying drawings.

Brief Description of the Drawings Figure 1 is a right top perspective exploded view of a first embodiment of apparatus for cutaneous blood pressure measuring apparatus.

Figure 2 is a top view of the apparatus of Figure 1. Figure 3 is a right side view of the apparatus of Figure 1.

Figure 4 is a left side view of the apparatus of Figure 1.

Figure 5 is a cross-sectional side view of the apparatus of Figure 1. Figure 6 is a bottom view of the isolation ring and the active surface of the transducer.

Figure 7 is a side cross section of an alternate embodiment having dual transducer.

Figure 8 is a second alternate embodiment of the present invention.

Making reference to Figures 1 through 6, the first embodiment of the apparatus, adapted for attachment to the middle finger, is shown.

The transducer support 10 comprises a hollow digit support member 12 open on at least one end and having an internal diameter slightly larger then the diameter of a middle finger. A spring biased assembly 14 is affixed to the opening 16 of the digit support member 12 to variably reduce the inner diameter of the opening of the digit support member 12.

Proximate to the other end of the digit support member 12 is a perpendicular hollow transducer support member 22. The upper end of the hollow transducer support member 22 is threaded 19 and has a slot 15 along one wall with calibration markings 20 along the slot 15.

The spring biased assembly 14 comprises a semicircular U-clamp 26, held in place by guide 17 attached to the digit support member 16. The upper end of the arms of the U-clamp 26 are attached to a flat cross member 28, either by screws, adhesive or other means. The assembly 14 is fitted over the first end 16 of the finger support member 12 with the U-portion of the U-clamp 26 fitted complementary to the bottom of the tubular digit support member 12. Fitted between the inside of the U-portion and the outside of the digit support member 12, is a biasing spring 30, mounted around guide 32. The spring 30 biases the U-clamp away from the tubular finger support member, pulling the cross-member 28 downward. A sponge material 31

is attached to the bottom of the cross member 28.

Within the transducer support member 22 is fitted cylindrical pressure transducer 24 which measures pressure differentials along the vertical axis. The pressure measuring transducer 24 fits slidably within transducer support member 22. The pressure transducer 24 has an isolation ring 21 at its lower end.

The isolation ring 21 surrounds the active surface 27 of the pressure transducer 24. This isolation ring projects beyond the active surface of the pressure transducer and serves to ^" substantially isolate the portion of the tissue within the isolation ring 21.

The isolation ring 21 also causes a portion of the tissue captured by the isolation ring 21 to protrude into the chamber formed by the side walls of the ring and the active surface of the pressure transducer 24 whose active surface 27 is thus tangentially oriented to the slightly domed isolated tissue. While in the preferred embodiment the isolation ring 21 completely surrounds the transducer 24, it may encircle less than 360 degrees of the transducer 24. When the pressure tranducer 24 is pressed against the cutaneous tissue the skin dorms a dome and fills the space between the isolation ring 21 and the active surface 27 of the pressure transducer 24. The active surface 27 of the transducer 24 should be substantially smaller than the inside diameter of the isolation ring 21 so as to permit the tissue to form a dome and not cause the tissue to flatten. The width of the isolation ring 21 is small in relationship to its inside diameter. The small width of the isolation ring 21 prevents flattening of the tissue, while at the same time promotes the formationof the domed portion of tissue within the isolation ring 21.

In the preferred embodiment of the invention the outside diameter of the isolation ring 21 is 3/4 inches and has a width of about 1/32 inches. The diameter of the active surface of the transducer 24 is 3/16 inches. The isolation ring 21 extends about 1/8 inches below the active surface 27 of the transducer. This promotes tight mechanical coupling between the domed portion of the tissue

and the active surface of the transducer. In the preferred embodiment the surface of the active surface 27 of the transducer 24 has a diameter of approximately one-fifth of the diameter of the isolation ring 21. Electrical leads from the transducer pass through slot 15 in the transducer support member 22 and are connected to a conventional recording device or oscilloscope, not shown. At the upper end of the pressure transducer 24 is a shoulder 34 for receiving one end of a coil spring 33 around central shaft 41, the other end of which is held by a shoulder inside cap 30. The cap 30 has internal threads 37 corresponding to the external threads 19 of the transducer support member 22. The coil spring 33 thus biases the pressure transducer 24 in a downward direction against the tissue of the patient. Calibration markings 20 on either the pressure transducer 24 or the electrical wires visually indicate the tension being applied by the spring 33 on the transducer 24. The transducer support member 22 may be transparent or have a transparent portion for viewing the marking means directly. An electrical switch S may be used in the event that a dual transducer configuration is employed, such as shown in Figure 7.

The operation of the device is as follows: The spring assembly 14 is depressed to permit the finger to be placed in the opening 16. The fleshy portion of the patient's finger is placed within the opening 16 of the finger support member 12 with the fingernail facing downward, presenting the soft fleshy portion of the finger to the active surface 27 of the pressure transducer 24. The spring assembly 14 is released, pressing the sponge material 31 against the finger holding the finger support member 12 in place relative to the finger

The pressure transducer 24 is now placed in the transducer support member 22, with the electrical wires extending through the slot 15. The cap 30 is placed on the transducer support member 22. The isolation ring 21 and the active surface 27 of the pressure transducer 24 are not pressed against the cutaneous tissue of the finger by the

spring 33.

The electrical lead is connected to a conventional strip chart recorder for recording the changes in blood pressure obtained by the pressure transducer 24. The cap 30 is then turned until the indicator marking means 20 is at the preferred position; the blood pressure reading shoud be approximately 75-100 mm Hg.

Referring to Figure 7, an alternative embodiment of the present invention is shown in which there is a modified apparatus for determining the spring pressure applied to transducer 24. A second transducer 29 is mounted above transducer 24, separated by spring 35 so that the active surface 37 of the second transducer 29 measures the pressure applied to the rear surface 39 of the first transducer 24, and the isolation ring 21. The output unit is switched to the first transducer 24 once the desired pressure is observed.

Referring to Fig. 8 a second embodiment of the present invention is shown. The central shaft 41 extends through an opening 43 in the top of cap 30. The central shaft 41 has markings 45 on it, either in measured increments or color coded, to indicated the tension on isolation ring 21.

The sensitivity and the fidelity of the cutaneous blood pressure waveforms obtained by this technique provides data on peripheral circulation heretofore inobtainable. With this apparatus one may clearly discern beat-to-beat changes in individual pulse pressure waves during physiologic and pharmocologic changes in tissue environment e.g. exercise, breathing, breath holding, active or passive smoking, drugs such as narcotics and anesthetics.

This type of data are not readily discernable with conventional- blood pressure monitoring apparatus.

The sensitivity of the device is such that the changes in a non-smokers blood pressure may be measured when he is near someone smoking a cigarette a condition known as "passive" smoking. For example, one of the inventors. Dr. Hon, has observed that at the start of passive smoking, his blood pressure, as determined by the present apparatus was

approximately 100 mm of Hg. After approximately seven (7) minutes of being in the presence of smoke his blood pressure rose to approximately 125 mm Hg. After the cigarette was removed. Dr. Hon's blood pressure continued to rise until it was approximately 150 mm Hg. of mercury two (2) minutes after the cigarette had been removed. His blood pressure remained at approximately 150 mm Hg. for about seven (7) more minutes and then continued to rise until it was approximately 165 mm Hg. after eleven (11) minutes. The blood pressure thereafter declined steadily, but did not return to baseline levels, until more than eighteen (18) minutes after the removal of the smoke from the cigarette. At this point, the possibility that the changes in the blood pressure was not psychologically motivated.

Regardless of the cause, this data would not be readily discernible by conventional blood pressure monitoring apparatus, even with invasive catheters. In addition, other detailed cardiovascular effects have been determined showing the effects of various drugs given to a patient during operations or labor. These new data provide detailed cardiovascular evaluation in situations where such an evaluation previously was limited to relatively gross external observations. The pressure measuring transducer 24 may be of a strain gauge type such as are available from Koeningsberg Instruments, Trans America Corporation or Gould, Inc., all of which are responsive to pressure applied to one surface. While a strain gauge is contemplated as the preferred form of carrying out the present invention it should be recognized that many other transducers are available which can measure pressure changes in a dome of tissue.

Guides for the adjacent fingers may be attached to the finger support member 12 to assist in the alignment of the finger support member 12. Such guides may be openings for the adjacent fingers or merely semicircular projections from the outside wall of the finger support member 12.

Other configurations of the present invention may be employed which do not depart from the inventive concept of

the present invention.