Automatic blood pressure measurement device with threshold compensation circuitry and method for performing the same

• US 4,469,107 A
• Filed: 06/01/1981
• Issued: 09/04/1984
• Est. Priority Date: 01/02/1979
• Status: Expired due to Fees

• Current Assignee: John Canavan, Raymond A. Asmar
• Original Assignee: John Canavan, Raymond A. Asmar
• Inventors: Canavan, John, Asmar, Raymond A.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/269,511
• Time in Patent Office: 1,191 Days
• Field of Search: 128/680-683
• US Class Current: 600/494
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/02233 Occluders specially adapted therefor tourniquets A61B17/132
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient

Abstract

A blood pressure measurement apparatus comprises electronic circuitry which converts an output from a pressure transducer into a digital display for both the systolic and diastolic blood pressure of an individual. The output of the pressure transducer contains an electrical DC voltage component with a superimposed AC voltage component during arterial blood flow. Sample and hold and logarithmic scaling circuits are used to properly sense the AC voltage over a wide range of values so as to eliminate improper sensing due to noise. A digital output display shows the individual'"'"'s systolic blood pressure while another display shows the current transducer reading which becomes set upon reaching the diastolic pressure. Control circuitry is used to sense occurrence of the systolic and diastolic pressures.

In one embodiment, the circuitry is enclosed in a wristwatch type case which also includes a constrictable band and an integral air bulb, resulting in an easily portable wrist-worn blood pressure measuring device. In another embodiment, the electronic circuitry is incorporated into a standard sphygmomanometer cuff to provide an automatic blood pressure measuring device.

Claims

1. A blood pressure measurement device comprising:

(A) an inflatable cuff positionable about a user'"'"'s limb and pressurizable so as to temporarily stop the flow of blood of the artery constricted by the cuff;

(B) means for pressurizing the cuff so as to produce a pressure within the cuff to totally occlude blood flow through the artery;

(C) means, activatable for gradually deflating the pressurized cuff to a pressure less than the diastolic pressure of the artery;

(D) a transducer coupled to the cuff and positioned to be placed in juxtaposition to the artery and having an electrical output simultaneously responsive to the pressure applied by the pressurizing means to the cuff and to the fluctuating pulse pressure components in the cuff pressure due to occluded arterial pressure pulses or to the presence of blood flowing through the artery in a partially occluded manner;

(E) means connected to the transducer electrical output for only passing the fluctuating pulse pressure components of the electrical output;

(F) means connected to the fluctuating pulse pressure components output means, for electrically amplifying the fluctuating pulse pressure components;

(G) means, coupled to the output of the amplifying means, operative by a first control pulse, for sampling and holding the electrical output from the amplifying means upon receipt of the first electrical pulse;

(H) a compensation circuit, connected to the output of the sample and hold means for modifying the electrical output of the sample and hold means so as to diminish the amplitude of the output as a function of the output signal, the output of the compensation circuit connected to the amplifying means so as to effectively reduce the output of the amplifying means as a function of the compensation circuit output;

(I) a threshold detector, connected to the amplifying means output for enabling the output of the detector during initial inflation of the cuff when the sample and hold means is inoperative and when the amplified fluctuating pulse pressure components as modified by the compensation means is greater than a predetermined value representing when blood flow begins after arterial occlusion and continuing until arterial blood flow is completely unoccluded;

(J) an analog to digital (A-D) converter receiving as one input the output of the transducer and as a second input the output of a threshold detector, the A-D converter generating digital output signals representative of the sensed blood pressure when the second input is enabled;

thereby generating signals representing the systolic blood pressure, the diastolic blood pressure, and blood pressures between the two as the deflating means is operative, as well as for indicating the cuff pressure during initial inflation of the cuff by the pressurizing means;

(K) a first display connected to the digital output signal of the A-D converter for generating a visual display of each output of the A-D converter and thereby maintaining the diastolic blood pressure reading upon termination of the threshold detector output signals;

(L) means, connected to the output of the threshold detector and energizable after initial cuff inflation, for generating the first control pulse and for generating at least a second control pulse when the threshold detector output is first generated after the first control pulse is generated;

(M) a second display for generating a digital output visual display of the systolic blood pressure; and

(N) means, connected to the output of the analog to digital converter, to the control means for sensing the second control pulse from the control means, and to the second display, for storing and driving the second display upon activation by the second control pulse;

whereby the first display shows the blood pressure in the cuff as the cuff is initially pressurized and also displays each blood pressure reading as the cuff pressure is reduced to and below the systolic pressure point, and latching the blood pressure reading upon receipt of the diastolic blood pressure; and

wherein the second display shows the systolic blood pressure and maintains this reading until the unit is de-energized.

2. A blood pressure measurement device as defined in claim 1, wherein the pressurizing means is an air pump and wherein a first switch has a position to initially energize the device except for the control means, so that the threshold detector will generate an output pulse during pumping of the air pump and thereby display on the first display the pressure within the cuff as the cuff is being pressurized and wherein the control means is energized by a second switch which is activated after pressurization of the cuff exceeding an arterial occluding pressure so as to then initiate the sample and hold and compensation circuitry of the present invention.

3. A blood pressure measurement device as defined in claims 1 or 2, wherein the compensation means performs a reduction of the input signal to the amplifying means as a logarithmic function of the output amplitude of the amplifying means.

4. A blood pressure measurement device as defined in claim 3, wherein the compensation means reduction of the input signal to the amplifying means causes the output of the amplifying means to be less than the predetermined value of the threshold detector when the artery is totally occluded.

5. A blood pressure measurement device as defined in claims 1 or 2, wherein the means for generating control pulses generates a third control pulse after the second control pulse is generated and wherein the means for storing and driving the second display further has means for receipt of the third control pulse, and wherein the second control pulse causes the digital value from the A-D converter to be stored in the storing and driving means and wherein this stored value is used to drive the second display upon receipt of the third pulse.

6. A blood pressure measurement device as defined in claims 1 or 2, wherein the inflatable cuff is mounted on a band dimensioned to be worn about the wrist of the user.

7. A blood pressure measurement device as defined in claim 6, wherein the pressurizing means comprises an inflatable air bladder and wherein the activatable means for gradually deflating the pressurized cuff is a needle valve.

8. A blood pressure measurement device as defined in claim 6, wherein the band incorporates hook and loop area fastening means.

9. A blood pressure measurement device as defined in claim 1, wherein the transducer comprises a piezoelectric pressure sensor.

10. A method of measuring the blood pressure of a user comprising the steps of:

(1) applying an external occluding pressure to a predetermined artery sufficient to temporarily stop the flow of blood;

(2) gradually decreasing the externally applied pressure so as to gradually allow blood to flow through the artery in a partially occluded manner until a point of totally unoccluded blood flow is attained;

(3) electrically sensing the applied pressure and the fluctuating pulse pressure caused either by the presence of a heart beat induced blood pressure variation during total occlusion of the artery or due to the presence of heart beat induced blood flowing through the artery;

(4) electrically filtering the output of step 3 so as to pass only the fluctuating pulse pressure components;

(5) electrically amplifying the fluctuating pulse pressure components;

(6) logarithmically reducing the electrically amplified pulse pressure component after an external occluding pressure has been obtained so as to filter to a value less than a first predetermined value the amplified pulse pressure of the totally occluded artery;

(7) enabling a detector output as the occluding pressure is applied to the predetermined artery and when the amplified fluctuating pulse pressure components are greater than the first predetermined value, which after initial arterial occlusion represents the systolic blood pressure occurrence, and disabling the detector output when the pressure component is less than this value, representing the diastolic blood pressure occurrence;

(8) generating a digital electrical signal from the sensed applied pressure and fluctuating pulse pressure when the detector signal is first enabled as the occluding pressure is applied to the predetermined artery so as to originally represent the occluding pressure applied to the artery and later to represent the systolic blood pressure, and continuing to generate digital signals for each heart beat after the systolic blood pressure signal has been generated until the detector signal is disabled, at which point the diastolic blood pressure digital signal is generated; and

(9) digitally displaying the digital electric signals representing initial occlusion of the artery, the systolic and diastolic blood pressures, and blood pressures between the systolic and diastolic pressures.