WO1993004625A1

WO1993004625A1 - Noninvasive temporal artery blood pressure sensor assembly

Info

Publication number: WO1993004625A1
Application number: PCT/US1992/007279
Authority: WO
Inventors: Alexander Borsanyi; Phillip D. Baker; Dwayne R. Westenskow; Nancy Smith
Original assignee: Baxter International Inc.; University Of Utah
Priority date: 1991-08-30
Filing date: 1992-08-27
Publication date: 1993-03-18

Abstract

A noninvasive sensor assembly is provided for measuring the blood pressure in the patient's superficial temporal arteries. The device comprises generally a support base (10), a sensor bladder (12) disposed within the support base (10), a transducer (13), a holding bladder (16), and headband (62) for securing the device to the patient's head. Optionally, a compression plate (14) is provided, the compression plate (14) serving to form an improved contact surface between the support base (10) and the headband (62). The holding bladder (16) serves to attenuate noise and artifacts from exterior sources while isolating the support base (10) against the patient's scalp.

Description

NONINVASIVE TEMPORAL ARTERY BLOOD PRESSURE SENSOR ASSEMBLY

BACKGROUND OF THE INVENTION FIELD: This invention relates generally to measurement of a person's blood pressure and more specifically to a device and related method for measuring blood pressure in the superficial temporal artery without the discomfort, inaccuracies and inherent dangers of using a standard occlusive blood pressure arm cuff.

PRIOR ART: Measurement of a patient's blood pressure is one of the most fundamentally necessary and well-recognized medical procedures. Blood pressure reflects not only the functionality of the heart as a pump, but the state of the entire vascular system as well. Hence, devices for measuring blood pressure have become well known in the art.

Perhaps the most common of these devices is the occlusive arm cuff, wherein the arm is modeled as a cylindrical structure composed of an incompressible fluid. Pressure in the occlusive cuff is assumed to be transmitted through the tissue of the arm without attenuation and thus to deliver a calibrated, uniformly distributed, and variable pressure to the wall of the artery. However, validation of this assumption is very difficult and there appears to be indirect evidence that it is at least partly invalid.

The occlusive arm cuff is a relatively simple device comprising a rubber bladder enclosed in a fabric cover. The cuff is wrapped around the arm and secured with suitably fasteners. Although the occlusive cuff is not a complicated device, its use is complicated by the fact that failure to select the proper size cuff for a patient can result in significant errors in blood pressure measurements. For example, it has been observed that there is a minimum cuff width beyond which further narrowing of the cuff results in an increasing overestimation of blood pressure. This phenomenon has been related to pressure dissipation, i.e. that the pressure profile transmitted to the wall of the artery is not uniform and that cuff pressure is dissipated in the tissue of the arm, particularly at the edges of the occlusive cuff. Also, occlusive cuf s can be extremely uncomfortable and freguent cycling of blood pressure readings through this device has been associated with nerve trauma and venous congestion. Another device for measuring blood pressure is typified by U.S. Patent No. 3,704,708. Therein an apparatus is disclosed which operates under the theory that a blood vessel will transmit an equal hydrostatic pressure in all directions, if the pressure producing source is suitable confined. Under this assumption, when a plate is pressed down on a pressurized duct so as to flatten the duct at least in part, then the force required to flatten that area divided by the area is the measure of the internal pressure of the duct. However, in order for this device to operate properly, the transducer, which transfers the force of the pressurized blood vessel to a measuring device, must be centered directly over the blood vessel. Otherwise, an inaccurate reading is registered. Also, the '708 device is unduly susceptible to environmental elements such as temperature and moisture, which affect the performance of the material in the transducer. Furthermore, this device does not take into account exterior noise and artifacts, such as patient movement and pulsation of other nearby arteries, which can have a dramatic adverse effect on measurement readings. Finally, and most important, the pressure exerted by the device cannot be varied, thus precluding an internal pressure reading at more than a single externally induced pressure level. Because noninvasive methods of estimating blood pressure are generally not traumatic and present little risk to the patient, they are often used instead of the invasive method, which requires that a catheter or needle be inserted into an artery. A major disadvantage associated with noninvasive methods has been their lack of close agreement with actual blood pressure as would be measured by invasive methods. In addition, lack of close agreement also exists among the different noninvasive methods, further adding to the uncertainty of any particular reading derives.

Oscillometry has become the preferred method for automatic, noninvasive blood pressure monitoring, as described in United States Patents 3,903,872; 4,009,709; and 4,074,711 each of which is incorporated herein by reference. It has been estimated that there are well over one hundred and fifty thousand (150,000) automatic oscillometric noninvasive blood pressure devices in the United States alone. One advantage of the oscillometric method over other noninvasive methods is its ability to estimate not only diastolic and systolic pressures, but also mean pressure.

Conventional oscillometric blood pressure monitors use an inflatable air filled occlusive cuff that is placed around a limb, usually the upper arm. Small oscillations in the cuff pressure, which correspond to intraarterial pulses in the artery underlying the- cuff, are recorded while the cuff pressure is increased from a pressure below diastolic to a pressure above systolic. As is characteristic of oscillometric waveforms, the cuff pressure oscillations initially increase in amplitude with increasing cuff pressure.

Oscillometric waveforms, however, have been found to be susceptible to artifacts and noise from a variety of sources. It is readily apparent that the processing of artifacts and noise interfering with quality signals decreases the accuracy of any estimation of blood pressure. Such, noises and artifacts can be caused not only'by patient movement during the test but by signals sent out by peripheral blood vessels also contained within the test zone.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION Accordingly, a principal object of the present invention is the provision of a blood pressure measuring device which is easily positioned over the superficial temporal artery, from which accurate representative measurement is taken.

Another important object of this invention is to create a device which is not susceptible to common environmental changes.

Another principal object is to provide a blood pressure measurement device which suppresses exterior noises and artifacts to provide a more accurate signal.

Another major object of this invention is the provision of a more comfortable method of measuring blood pressure which avoids venous congestion and nerve trauma.

These and other objects of this invention are realized in a localized blood pressure measuring sensor assembly for preferred use over the superficial temporal artery of the scalp. The sensor assembly comprises generally a support base which defines a cavity, a sensor bladder contained in the cavity, a holding bladder disposed atop the support base, a compression plate, and a transducer.

The holding bladder is situated between the support base and rigid compression plate, the compression plate engaging the headband which secures the sensor assembly to the patient's scalp. The holding bladder serves to isolate the support base and sensor bladder against the temporal artery, and also absorbs much of the exterior noise and artifacts associated with oscillometric monitoring. The sensor bladder is formed of a nonelastiσ material such as polyvinyl chloride and serves, when inflated, to sense pressure changes within the subject artery. In sensing pressure changes, the sensor bladder sends signals which vary according to pressure variations within the artery. The transducer detects the signals and converts them into readable oscillometric waveforms. The support base also has two continuous hinged legs for contracting and conforming to the scalp of the patient to be tested.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanied drawings in which:

FIGURE 1 is a front perspective view of a preferred embodiment of the sensor assembly for measuring blood pressure shown attached to a patient's superficial temporal artery by a flexible, non-stretching, adjustable headband; FIGURE 2 is an enlarged, exploded plan view of the sensor assembly of Figure 1;

FIGURE 3 is a bottom plan view of the sensor assembly of Figure 1;

FIGURE 4A is a frontal cross-sectional view of a model illustrating the operating principles of the present invention;

FIGURE 4B is a side cross-sectional view of the model of Figure 4a;

FIGURE 5 is a side elevational view of a typical patient's head illustrating the proper placement of the preferred sensor over the superficial temporal artery;

FIGURE 6 is a front elevational view of the support base; and FIGURE 7 is a schematic representation of the sensor assembly of the present invention shown attached to exteriorly contained air pumps and transducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to the drawings wherein like numerals are used to denote like components throughout. As best seen in Figures 2 and 3, the device of the present invention comprises generally a support base 10, an inflatable sensor bladder 12, a transducer 13, a compression plate 14, and an inflatable holding bladder 16, each of which is hereinafter described in greater detail. The device is secured against the patient's skin by means of a flexible, nonstretching, adjustable headband 62 (Figure 1) .

Support base 10 is of rigid construction, preferably plastic, and comprises two continuous parallel legs 18 and 20. As shown in Figure 2, legs 18 and 20 may have continuous, inwardly slanting, raised skin contracting feet 22 and 24, respectively, which follow generally the contour of a patient's skull. Advantageously, each foot 22 and 24 is hingedly connected to legs 18 and 20 of bottom face 21, respectively, to permit accommodation to differently shaped skulls. As also seen in Figure 2, support base 10 defines a cavity 26 wherein sensor bladder 12 is contained. Cavity 26 is open at and accessed through bottom face 21 of support base 10. In plan, as shown in Figure 4, support base 10 may include top and bottom notches 28 and 30, each of which allows the sensor assembly to fit around the patient's ear as it is placed in a proper position to measure blood pressure in the superficial temporal artery. Notches 28 and 30 are useful to properly position and orient the sensor bladder over the temporal artery. Obviously, these notches may not be necessary when the device is used over other superficial arteries. Support base 10 further comprises a top face 27 oriented away from the patient, and apertures 32 and 34 drilled or otherwise formed in short ends 36 and 38, respectively, of base 10 and leading to cavity 26.

Inflatable sensor bladder 12, as explained, is disposed in cavity 26 of support base 10 so as to be responsive to arterial activity when placed on the skin of the patient. The preferred material from which it is constructed is nonexpandable and advantageously comprises polyvinyl chloride. In one preferred embodiment inflatable sensor bladder 12 is actually two independently inflated bladders 40 and 42, or more, as shown in Figure 2, stacked, one on top of the other in a series, so constructed by heat sealing thin layers of material together using a metal stamp.

As seen in Figure 7, bladders 40 and 42 are each connected by way of a sufficient length of tubing 44 and 46, which exit through apertures 32 and 34, respectively, to a standard air pump 48 and pressure transducer 13, both of which are well-known in the art. Sensor bladder 12, which fills cavity 26 when inflated, makes direct contact with the patient's skin and is used both to occlude the artery wherein blood pressure is to be measured and to respond to pressure variations in the artery in the form of varied signals. The use of stacked sensor bladders 40 and 42 allows for more even expansion during inflation, which is necessary to completely fill the cavity 26 in base support 10 and uniformly contact the patient's skin. In another preferred embodiment, sensor bladder 12 takes the shape of a single accordion bellows. Such a shape provides fairly uniform expansion of bladder 12 within the cavity 26 during inflation, especially in light of the nonexpandable nature of the material from which it is constructed. The gap or volume that sensor bladder 12 must expand and fill varies with each patient depending upon the particular geometry of that patient's head. The ability of bladder 12 to expand with little or no increase in the internal pressure of the bladder is important in delivering a calibrated and uniform pressure to the surface of the skin. The objective sought to be obtained is to keep the surface of the bladder as flat as possible so that the pressure applied across the bladder wall is equivalent to the pressure in the bladder and the contact area between the skin and the bladder remains constant as the bladder pressure is increased during a blood pressure determination. It has been found that the best results occur when the total inflated volume of sensor bladder 12 is less than five milliliterε; more specifically, between one and three milliliters.

The transducer 13 detects the arterial activity of varied signals measured by the sensor bladders 40 and 42, denoting pressure variations in the subject artery. These signals are then converted into readable oscillometric waveforms by a standard Wheatstone-type bridge from which the systolic, diastolic and means aspects of the patient's blood pressure are measured.

As best shown in Figure 2, inflatable holding bladder 16 is disposed adjacent the top face 27 of the support base 10 opposite feet 22 and 24. Holding bladder 16 is advantageously constructed of any durable impervious material and has a capability of expanding approximately two centimeters in height when inflated. Its main function is to supply an evenly distributed force on the support base 10 to maintain support base 10 in an independent static condition against the patient's skin while a blood pressure determination is being made. Holding bladder 16 is manually inflated through a tube 52, which is attached at its opposing end to an air pump 54 (see Figure 7) . Air pump 54 is actuated to inflate holding bladder 16 just before a blood pressure determination is made, i.e., just before sensor bladder 12 is inflated, and deflated immediately thereafter to minimize discomfort to the patient. Holding bladder 16 also functions as a noise suppressor. When inflated, the holding bladder 16 attenuates and absorbs noise and artifacts transmitted through a headband used to attach the sensor assembly to a patient's head. Sources of these noises and artifacts arise from patient motion, as well as peripheral arteries near the temporal artery pulsating beneath the headband 62. In prior art devices, pulsations from these arteries were apparently transmitted as changes in headband tension back through the headband to the transducer 13, causing inaccuracies in blood pressure readings.

Again referring to Figure 2, a stiff compression plate 14 is disposed atop holding bladder 16. The bottom surface 58 thereof, which is adjacent to and in contact with holding bladder 16, is relatively flat, whereas the top surface 60 is generally convex in complying with the curvature of the patient's head. Convex top surface 60 of compression plate 14 is engaged by a headband 62, as shown in Figures 1 and 2, which securely maintain the sensor assembly firmly in a substantially fixed position relative to the patient's skin over the temporal artery.

Headband 62 is advantageously separated into first and second major sections 62a and 62b, and is made adjustable by selectively joining the first and second major sections 62a and 62b with cooperating detachable adhering strips, such as Velcro (not shown) . The headband 62 is flexible to conform to the individual patient's head curvatures, and yet must necessarily be made of a non-stretching material in order to provide an accurate reading.

In applications over the superficial temporal artery, the sensor assembly is placed over either of the patient's ears and secured in placed by the headband 62. Caution must be taken to position at least a portion of sensor bladder 12 directly over the superficial temporal artery, which passes upward along the side of the head just in front of the ear, the artery then bifurcating into a frontal and parietal branch. The artery may be located prior to positioning of the sensor assembly by probing with the finger tips for a pulse in the described area. By using the referenced notches the approximate proper positioning can be accomplished by simply adjusting the notch 30 or 28 over the ear.

When the sensor assembly is properly positioned, air is pumped into the holding bladder 16 by air pump 54 to inflate and emit a downward pressure on support base 10. Before legs 18 and- 20 of support base 10 dig into the patient's scalp as a result of the inflating of holding bladder 16 to cause discomfort, sensor bladder 12 is also inflated by air pump 48, which alleviates a substantial portion of the pressure felt by the patient as a result of the inflating holding bladder 16.

As sensor bladder 12 inflated, an even downward pressure against the patient's scalp results and the subject artery is blocked, as modeled in Figures 5a and 5b. Gradually, the air is released from sensor bladder 12 to vary the pressure and to restore the flow of blood to the blocked artery. As the blood begins to flow again, resulting pulsations are registered on the pressure transducer 13. This aspect is the same as the conventional occlusive arm cuff procedure commonly used in the medical profession today. It will be apparent that this procedure is particularly advantageous for oscillometric waveform analysis in accordance with state of the art technology.

After readings have been taken, the holding bladder 16 is also deflated to minimize discomfort to the patient. If continuous readings are to be taken over an interval of time, the sensor assembly is advantageously left in place between the readings. However, when the desired number of blood pressure determinations have been made, the entire sensor assembly is removed. It is to be understood that the above described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements.

Claims

What is claimed is:

1. A device for noninvasively measuring a patient's blood pressure at the superficial temporal artery, the device comprising: a support base having a top face oriented away from the patient, and a bottom face

(i) for contacting the patient's skin, and (ii) which defines a cavity, said cavity being accessible through the bottom face, inflatable sensor means disposed in the cavity of the support base so as to be responsive to arterial activity when placed on the skin of the patient, the inflatable sensor means being capable of placement directly over the temporal artery in which the blood pressure is to be measured, transducer means capable of detecting the arterial activity and generating varied output signals which can be converted into readable oscillometric waveforms, an inflatable holding bladder disposed adjacent the top face of the support base, the holding bladder including means for supplying an evenly distributed force on the support base to maintain the support base in an independent static condition against the patient's skin, and headband means for maintaining the device in a substantially fixed position relative to the patient's skin.

2. A device according to Claim 1 wherein the headband has first and second major sections and is made adjustable by selectively joining the first and second major sections with cooperating detachable adherence means.

3. A device according to Claim 1 wherein the inflatable sensor means comprises at least one inflatable bladder.

4. A device according to Claim 3 wherein the inflatable bladder is constructed of a non-expandable material.

5. A device according to Claim 4 wherein the non- expandable material is polyvinyl chloride.

6. A device according to Claim 3 wherein the inflatable bladder is shaped as an accordion bellows.

7. A device according to Claim 1 further comprising a stiff compression plate having top and bottom surfaces, the bottom surface providing containment and rigid resistance to pressure forces developed by the inflatable holding bladder, and the top surface being convex and engaged by the securing means.

8. A device according to Claim 1 wherein the support base further comprises skin contacting feet hingedly connected to the bottom face thereof.

9. A method for noninvasively measuring the blood pressure of a temporal artery, said method comprising the steps of: a) temporarily securing a base support to the patient's skin over artery with securing means, the support base having a bottom face accessing a cavity containing inflatable sensor means, and a top face adjacent which an inflatable holding bladder is disposed, b) inflating the inflatable holding bladder such that the holding bladder supplies an evenly distributed force on the support base to maintain the support base in an independent static condition against the patient's skin, c) inflating the inflatable sensor means so as to be responsive to the arterial activity in the artery, and d) detecting the arterial activity in the artery as varied signals with transducer means which convert the same into readable oscillometric waveforms as pressure in the inflatable sensor means is gradually varied.

10. In a method of obtaining certain information about the blood pressure of a given person by means of a particular blood pressure technique in which a pressurizable pressure transducing bladder located adjacent and cooperating with the temporal artery of the person is used in combination with means for pressurizing the bladder in a controlled way in order to provide the desired information, the improvement comprising the steps of:

(a) providing a pressure transducing bladder within an open cavity of a relatively rigid bladder housing;

(b) placing said housing adjacent the outer skin of said person such that said bladder is adjacent said temporal artery;

(c) placing a holding bladder against said housing opposite said transducing bladder;

(d) securing said holding bladder in position against said housing;

(e) pressurizing said holding bladder sufficient to hold said transducing bladder in place adjacent said artery; and (f) pressurizing said transducing bladder in said controlled way for providing the desired information.

11. A blood pressure transducing assembly for use in a system for obtaining certain information about the blood pressure of a given person, comprising:

(a) relatively rigid means defining a cavity and including within said cavity a pressure transducing bladder positioned to engage the skin of said given person over the temporal artery; (b) a holding bladder positioned against said rigid means such that when the holding bladder is pressurized it holds said transducing bladder in position against the skin of said person over said temporal artery; and

(c) means for securing said holding bladder in position against said rigid means.