Method and apparatus for automatically determining pulse rate and diastolic and systolic blood pressure

Claims

We claim:

1. a device for detecting arterial pulsations in a subject's body comprising an outer rigid cylindrical shell to encircle a portion of a subject's body, a cuff including at least one substantially flat, flexible, inflatable, bladder, encircled and secured to the inside circumference of said shell to engage said body portion, a first tubular member having a first and second end, said first end of said tubular member engaging the interior of said bladder in a fluid-tight manner, said second end of said tubular member in fluid communication with a means for decreasing and increasing pressure in said bladder, a pressure control means cooperable with said means for decreasing and increasing pressure in said bladder and said interior of said bladder to control the pressure in said bladder, the improvement comprising a sensor in fluid communication with said interior of said bladder and responsive to arterially-induced pressure pulsations in said bladder for generating an electrical signal having an amplitude corresponding to said pulsations in said bladder, said sensor comprising a pressure transducer chamber and a pressure transducer, said pressure transducer having an arterial pulsation sensing end in fluid communication with the interior of said bladder in a fluid-tight manner to detect arterially-induced pressure pulsations in said bladder and to generate electrical signals having an amplitude corresponding to said pulsations, said bladder and a non-sensing end in fluid communication with the interior of the said pressure transducer chamber, a pressure equalization passageway in fluid communication with the interior of said bladder and the interior of said pressure transducer chamber, said pressure equalization passageway of sufficient size to allow equalization of pressure between said bladder and said chamber sufficiently to substantially reduce inflation pressure from impending upon said pressure transducer without interfering with detection of said arterially-induced pressure pulsations by said pressure transducer thereby eliminating any interference of inflation pressure with detecting of arterially-induced pressure pulsations in said bladder by said pressure transducer.

2. The device according to claim 1 wherein said pressure transducer is a condenser microphone.

3. The device according to claim 2 wherein said condenser microphone is an electret condenser microphone.

4. The device according to claim 1 wherein said pressure equalization passageway is of a sufficient size to allow from about 50.0 to about 70.0 percent pressure change between the interior of said bladder and the interior of the pressure transducer chamber to occur within about 150 to about 250 milliseconds.

5. The device according to claim 4 wherein said pressure change is from about 60 to about 65 percent and from about 190 to about 210 milliseconds.

6. The device according to claim 5 wherein the pressure change is 63 percent in 200 milliseconds when bladder inflation pressure in said bladder is at least about 50 mm Hg.

7. The device according to claim 1 wherein said device additionally contains an attenuator, said attenuator containing interior sides which coincides with exterior sides of said sensor, said attenuator containing one closed end, said closed end of said attenuator containing an attenuator passageway through said closed end of said attenuator in fluid communication with the interior of said bladder and said interior sides of said attenuator, said sensor in slideable contact with the interior sides of said attenuator, with the pressure transducer of said sensor in fluid communication with said attenuator passageway, said attenuator passageway being of sufficient size to allow arterially-induced pressure pulsations to pass from said bladder to said sensor while allowing said amplitude of said arterially-induced pressure pulsations to be reduced when said sensor slideably moves inside said attenuator away from said bladder thereby reducing said arterially-induced pressure pulsation amplitudes allowing the use of pressure transducers with different detecting sensitivities to said amplitudes.

8. A device for detecting arterial pulsations for utilization in a system for determining pulse rate and systolic and diastolic blood pressure including an outer, rigid, cylindrical shell to encircle a portion of a subject's body, a first cuff including a substantially flat, flexible, inflatable, bladder, encircled and secured to a first portion of the inside circumference of said shell to engage said body portion and a second cuff including a substantially flat, flexible, inflatable, bladder, encircled and secured to a second portion of the inside circumference of said shell to engage said body portion, a first tubular member having a first and second end, said first end of said first tubular member engaging the interior of said first bladder in a fluid-tight manner, said second end of said first tubular member in fluid communication with a means for increasing and decreasing pressure in said first and second bladders, a second tubular member having a first and second end, said first end of said second tubular member engaging the interior of said second bladder in a fluid-tight manner, said second end of said second tubular member in fluid communication with said means for increasing and decreasing pressure in said first and second bladders, a pressure control means cooperable with said means for increasing and decreasing pressure in said first and second bladders and said interior of said second bladder to control pressure in said second and first bladders, the improvement comprising a first sensor in fluid communication with said first bladder and responsive to arterially-induced pressure pulsations in said first bladder for generating a first electrical signal having an amplitude corresponding to said pulsations in first said bladder, said first sensor comprising a first pressure transducer chamber and a first pressure transducer, said first pressure transducer having an arterial pulsation sensing end in fluid communication with the interior of said first bladder to detect arterially-induced pressure pulsations in said first bladder and to generate a first electrical signal having an amplitude corresponding to said pulsations in first bladder and a non-sensing end of said first pressure transducer in fluid communication with the interior of said first chamber in a fluid-tight manner, a first pressure equalization passageway in said first chamber in fluid communication with the interior of said first bladder and the interior of said first pressure transducer chamber, said first pressure equalization passageway of a sufficient size to allow equalization of pressure between said first bladder and said first chamber sufficiently to substantially reduce inflation pressure from impending upon said first pressure transducer without interfering with detection of said arterially-induced pressure pulsations by said first pressure transducer thereby eliminating any interference of inflation pressure with detection of arterially-induced pressure pulsations in said first bladder by said first pressure transducer, a second sensor in fluid communication with said second bladder and responsive to arterially-induced pressure pulsations in said second bladder for generating a second electrical signal having an amplitude corresponding to said second bladder pulsations, said second sensor comprising a second pressure transducer chamber and a second pressure transducer, said second pressure transducer having an arterial pulsation sensing end in fluid communication with the interior of the second bladder to detect arterially-induced pressure pulsations in said second bladder and generate a second electrical signal having an amplitude corresponding to said second bladder pulsations and a non-sensing end of said second pressure transducer in fluid communication with the interior of said second chamber in a fluid-tight manner, a second pressure equalization passageway through a wall in said second chamber in fluid communication with the interior of said second bladder and the interior of said second pressure transducer chamber, said second pressure equalization passageway of a sufficient size to allow equalization of pressure between said second bladder and said second chamber sufficiently to substantially reduce inflation pressure from impending upon said second pressure transducer without interfering with detection of said arterially-induced pressure pulsations by said second pressure transducer thereby eliminating any interference of inflation pressure with detection of arterially-induced pressure pulsations in said second bladder by said second pressure transducer.

9. The device according to claim 8 wherein said first pressure transducer is a condenser microphone.

10. The device according to claim 9 wherein said condenser microphone is an electret condenser microphone.

11. The device according to claim 8 wherein said first pressure equalization passageway is of a sufficient size to allow from about 50.0 to about 70.0 percent pressure change between the interior of said first bladder and the interior of said first pressure transducer chamber to occur within from about 150 to about 250 milliseconds.

12. The device according to claim 11 wherein the pressure change is 63.0 percent in 200 milliseconds when bladder inflation pressure in said bladder is at least 50 mm Hg.

13. The device according to claim 8 wherein said device additionally contains a first attenuator, said first attenuator containing interior sides which coincide with the exterior sides of said first sensor, said first attenuator containing one closed end, said closed end of said first attenuator containing a first attenuator passageway through said closed end of said attenuator in fluid communication with the interior of said first bladder and said interior sides of said first attenuator, said first sensor in slideable contact with the interior sides of said first attenuator with the pressure transducer of said first sensor in fluid communication with said first attenuator passageway, said first attenuator passageway being of a sufficient size to allow arterially-induced pressure pulsations to pass from said first bladder to said first sensor while allowing said amplitude of said arterially-induced pressure pulsations to be reduced when said first sensor slideably moves inside said first attenuator away from said first bladder thereby reducing said arterially-induced pressure pulsation amplitutes allowing the use of pressure transducers in said first sensor with different detecting sensitivities to said amplitudes.

14. The device according to claim 8 wherein said second pressure transucer is a condenser microphone.

15. The device according to claim 14 wherein said condenser microphone is an electret condenser microphone.

16. The device according to claim 8 wherein said second pressure equalization passageway is of a sufficient size to allow from about 50.0 to about 70.0 percent pressure change between the interior of said second bladder and the interior of said second pressure transducer chamber to occur within from about 150 to about 250 milliseconds.

17. The device according to claim 16 wherein the pressure change is 63.0 percent and in 200 milliseconds when bladder inflation pressure in said bladder is at least about 50 mm Hg.

18. The device according to claim 8 wherein said device additionally contains a second attenuator, said second attenuator containing interior sides which coincide with the exterior sides of said second sensor, said second attenuator containing one closed end, said closed end of said second attenuator containing a second attenuator passageway through said closed end of said second attenuator in fluid communication with the interior of said second bladder and said interior sides of said second attenuator, said second sensor in slideable contact with the interior sides of said second attenuator with the pressure transducer of said second sensor in fluid communication with said second attenuator passageway, said second attenuator passageway being of a sufficient size to allow arterially-induced pressure pulsations to pass from said second bladder to said second sensor while allowing said amplitude of said arterially-induced pressure pulsations to be reduced when said first sensor slideably moves inside said second attenuator away from said second bladder thereby reducing said arterially-induced pressure pulsation amplitutes allowing the use of pressure transducers in said first sensor with different detecting sensitivities to said amplitudes.

19. A method for automatically determining pulse rate and systolic and diastolic blood pressure of a subject including a device employing an automatic arterial pulsation monitoring cuff to encircle a portion of said subject's body containing at least a first and second selectively inflatable bladders each containing a sensor reponsive to arterially-induced pressure pulsations in said cuff for generating electrical signals having amplitudes corresponding to the pulsations in said bladders, said second bladder in fluid communication with a sensor responsive to pressure in said second bladder for generating electrical signals corresponding to the pressure in said second bladder, said bladders interconnected with a pressurizing system, all of said sensors connected electrically to a system for automatically processing the electrical signals from said sensors and automatically inflating and deflating the bladders and a means for calculating the pulse rate and the systolic and diastolic pressure of the human subject comprising the steps of:

(a) positioning said first and second bladders in said cuff in relationship to each other such that said second bladder is an occluding bladder;

(b) secondly simultaneously inflating at least said first and second bladders to a determined pressure at which inflation ceases and at which said second occluding bladder occludes blood flow resulting in said sensor in said first bladder sensing no arterially induced pressure pulsation amplitudes;

(c) thirdly deflating said first and second bladders at a predetermined rate;

(d) during steps (b) and (c) continuously generating electrical signals having an amplitude corresponding to the pulsations in the bladders and the pressure in said second bladder and measuring the time duration between each pulsation;

(e) during steps (b) through (c) monitoring continuously said signals and said time durations;

(f) during steps (b) through (c) storing said signals and said time durations;

(g) fourthly terminating the deflating step (c) at a predetermined pressure and then releasing the pressure from said first and second bladders;

(h) then processing said stored signals and said time durations to determine the subject's pulse rate, systolic blood pressure and diastolic blood pressure comprising the steps of:

(1) first determining the systolic pressure of the subject by determining inflation pressure in the second bladder when a first pulsation is detected in said first bladder after deflation begins in step (c);

(2) secondly, examininig amplitudes of all pulsations detected in said second bladder during step (c) and first determining an increase in amplitudes and then a decrease in amplitudes and then constant amplitudes, and then determining the diastolic pressure of the subject by determining the inflation pressure in said second bladder when a first pulsation at the beginning of the constant amplitudes is detected in said second bladder; and

(3) examining the time duration between all pulsations during step (c) and then caculating the pulse rate of the subject.

20. The method according to claim 19 wherein the pressure in step (b) increases to about 50 mm Hg before steps (d), (e) and (f) begin.

21. The method according to claim 20 comprising the additional step of determining the occluding pressure of the subject by examining amplitudes of all pulsations detected in said second bladder in step (b) and first determining an increase in amplitudes of said pulsations and then a maximum amplitude and then a decrease in amplitudes, and then determining the occluding pressure of the subject by determining the inflation pressure in said second bladder when these amplitudes drop below a predetermined level and pulsations cease in said first bladder, said predetermined level comprises one-half of said maximum amplitude and said occluding pressure is the predetermined pressure at which inflation ceases in step (b).

22. The method according to claim 21 wherein in step (c) the predetermined rate of deflating is from about 2 to about 4 mm Hg per second.

23. The method according to claim 22 wherein the predetermined pressure for terminating the deflation step (g) is 50 mm Hg.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an automatic apparatus and method for detecting arterially-induced pulsations and automatically determining the pulse rate, and systolic and diastolic blood pressure.

2. Description of the Prior Art

It is known in the prior art that arterially-induced pressure pulsations may be detected by means of an electrostatic microphone responding to the pressure pulsations in a compressing fluid as disclosed in Bouche U.S. Pat. No. 2,851,030. Further, the use of microphones and electrostatic pressure conversion elements are disclosed in Luisada U.S. Pat. No. 2,297,905 and Speaker, et al U.S. Pat. No. 2,452,799. Further, Zuidena U.S. Pat. No. 2,989,051 uses pulsation pressure information along with cuff pressure information to derive blood pressure reading. Utilizing this same approach in most recent art is shown in the following references: German Pat. No. 3,008,601; Nakayama U.S. Pat. No. 3,920,004; Link et al U.S. Pat. No. 4,009,709; Link et al U.S. Pat. No. 4,074,711; Wohltjen et al U.S. Pat. No. 4,078,551; Gangirard et al U.S. Pat. No. 4,177,801; Danna et al U.S. Pat. No. 4,261,368; Jewett U.S. Pat. No. 4,290,434; Ramsey III U.S. Pat. No. 4,349,034; Ramsey III U.S. Pat. No. 4,360,029; Jewett U.S. Pat. No. 4,417,586; Nunn et al U.S. Pat. No. 4,427,013.

The need to measure both the systolic and diastolic blood pressure and the pulse rate utilizing an automatic procedure was required.

A unique method for not only determining the pulse rate but determining the systolic and diastolic blood pressure was discovered.

It was further discovered that upon inflating the bladders in the instant invention that the pressure within the bladder would impend upon the pressure transducer. More specifically, the pressure inside the bladder impends upon a diaphragm located in the pressure transducer, preventing the diaphragm from responding to arterially-induced pressure pulsations in the bladder. The inflation pressure which is much greater than the arterially-induced pressure pulsations in the bladder, interferes or prevents the diaphragm from reacting or flexing in response to these arterially-induced pulsations. It was discovered that a pressure equalization passageway was necessary in order to equalize the pressure between the interior of the bladder and the interior of the pressure transducer chamber. This passageway allows equalization of pressure on both sides of the pressure transducer diaphragm. The size of the passageway is critical since it must be of a sufficient size to allow pressure equalization between the inflation pressure in the bladder and the interior of the pressure transducer chamber and not interfere with the pressure transducer diaphragm reacting to or sensing the arterially-induced pulsations generated in the bladder. Further, it was discovered that pressure transducers have different sensitivities to arterially-induced pulsation amplitudes. Consequently a device was discovered for use in conjunction with the instant sensor for decreasing the amplitude of the arterially-induced pulsation amplitudes such that pressure transducers of varying sensitivity may be used.

The prior art disclosed many methods for determining blood pressure and pulse rate, three of the most pertinent prior art references are the following: Croslin U.S. Pat. No. 4,271,844; Croslin U.S. Pat. No. 4,326,537 and Croslin U.S. Pat. No. 4,407,297. These are all related companion patents.

In the above mentioned patents, each is comparing the detective sequence of the relative amplitudes of a predetermined number of blood pressure pulses with a plurality of known valid sequences to determine if the detected sequences are valid. In the instant invention, the above known valid sequences, is not a fixed number derived from data. Further, in the above patents, if the detected sequence is determined to be valid, then the systolic pressure is determined to be the registered occluding pressure at the onset of a predetermined blood pressure pulse. This determination of the occluding pressure in the instant invention is determined at a different point of reference. Further, as set forth in these references, in determining the diastolic pressure, to be the registered occluding pressure at the onset of a pre-selected pulse, in a predetermined number of last pulses when the representative value is less than the threshold value, this does not disclose the instant method. Further, and most imporantly, these patents are concerned with the detection of the Korotkoff sound whereas the instant invention is concerned with detecting arterially-induced pressure pulsations as distinguished from audio sound detection. Further, in the above patents, these methods are registering the value of a sample which is generated at the start of a blood pressure pulse and maintained for the duration of at least several, but not all, of the succeeding blood pressure pulses. In the instant invention, all the arterially-induced pulsations and pressures are stored and used to compute blood pressure values and pulse rate after the cycle has been completed. In the above patents, these methods are merely taking a window from the data and using the figures from this window to determine blood pressure. The methods disclosed in the above patents are discarding all the other readings outside this window area. Further, these patents are deriving the "height" of a blood pressure pulse by substracting the respective value registered in their step (c) from the larger sample value of the respective blood pressure pulse and maintaining such height for the duration of at least several, if not all, of succeeding blood pressure pulses and then taking slight variations on that one sensor signal. In the instant method, there are separate sensors used in determining the occluding and diastolic pressure and the systolic pressure.

As to U.S. Pat. No. 3,978,848 which discloses a blood pressure and rate monitor wherein the inflatable cuff contains a pressure responsive transducer that performs two functions. The first function is providing a first signal corresponding to the gauge pressure in the cuff and the second function provides a second signal corresponding to variation in the cuff pressure produced by expansion and contraction of the occluding artery due to the pumping action of the heart.

U.S. Pat. No. 3,905,354 claims a method of automatically measuring the patient's systolic and diastolic blood pressure by several steps including generating quantized pressure signals in response to pressure pulses to provide individually defined pressure signals of a uniform amplitude.

In both U.S. Pat. No. 3,978,848 and U.S. Pat. No. 3,905,354 neither disclose apparatuses or methods for aleviating the problem of the bladder inflation pressure impending upon the pressure transducer thereby preventing the pressure transducer from detecting arterially-induced pulsations and generating electrical signals having amplitudes corresponding to the pulsations. Further, the above prior art discloses no apparatus or method for adjusting the sensitivity of pressure transducers to the amplitudes of these pulsations. Further, the above prior art does not disclose or suggest the instant method.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide an automatic apparatus and method for determining, pulse rate and systolic and diastolic blood pressure. The apparatus, the sensors of which, are not prevented from sensing arterially-induced pressure pulsations by bladder inflatable pressure. A further object of the invention is to provide a method for utilizing the entire arterially-induced pulsations history and pressure history within the bladder received from sensors within an apparatus to determine pulse rate and systolic and diastolic blood pressure.

The principal upon which the present device is based is first explained. The device is an automatic device for measuring pulse rate and the systolic and diastolic blood pressures of a human subject. The human subject preferably places his left arm into a rigid cylindrical shell preferably containing two inflatable bladders. The first and second bladders being positioned such that the second bladder when inflated occludes the blood flow to the first bladder. Consequently, the second bladder is located closest to the elbow of the subject and the first bladder is located closest to the hand of a subject, when the subject's forearm is placed into a rigid cylindrical shell containing the two bladders. The subject presses a start button on the apparatus which energizes a microcomputer. The computer energizes a pressure pump which pumps fluid into a fluid volume chamber. The fluid is preferably air. The fluid volume chamber allows fluid to escape through two orifices which are connected separately via fluid tubes or air tubes to each of the two inflatable bladders. As the fluid chamber fills with fluid both the first and second bladders simultaneously fill with fluid or air. The second bladder refered to as the occluding bladder or diastolic bladder additionally is connected via a fluid or air tube to a gauge pressure transducer which is connected to the microcomputer. Both the first and second bladder continue to be inflated by fluid from the fluid volume chamber to a pressure at which the second bladder occludes blood flow. During the inflation step, at a predetermined pressure, the microcomputer begins to process electrical signals generated by the sensors in both bladders. The occluding of blood flow by the second bladder results in the sensor in the first bladder sensing no arterially-induced pressure pulsation amplitudes. At this point, the microcomputer de-energizes the pressure pump and inflation ceases. Then the microcomputer energizes a solenoid valve connected to the fluid volume chamber. This solenoid valve opens and air or fluid is released, at a predetermined rate, from the fluid volume chamber through a deflation control orifice. As this fluid is released from the fluid volume chamber deflation begins in the first and second bladders at the same predetermined rate. During both the inflation and deflation step the microcomputer receives and stores electrical signals from the sensors in both bladders. The electrical signals from the sensors have amplitudes corresponding to the pulsation in the bladders. The gauge pressure transducer, located in fluid communication with the second bladder generates electrical signals corresponding to the pressure in the second bladder and sends these electrical signals to the microcomputer. Further, the time duration between each pulsation amplitude is received and stored by the microcomputer. These electrical signals and time durations are processed by the microcomputer after the deflation step has been completed. At a predetermined pressure the deflation step is terminated. At the end of the deflation step, the microcomputer activates two solenoid valves. One of these valves is located in the fluid or air line or tube between the fluid volume chamber and the first bladder. The other solenoid valve is located in the fluid or air line or tube between the fluid volume chamber and the second bladder. These valves are opened to allow fluid in the system in both bladders to escape. At this point the subject may remove the forearm from the rigid cylindrical shell since the bladders have now been completely deflated. After completion of the above procedures, the microcomputer processes all the stored signals and time durations and then calculates the subject's pulse rate, systolic blood pressure and diastolic blood pressure. The processing and calculating involves the steps