Oscillometric blood pressure monitor which acquires blood pressure signals from composite arterial pulse signal

• US 5,680,870 A
• Filed: 01/04/1995
• Issued: 10/28/1997
• Est. Priority Date: 01/04/1995
• Status: Expired due to Fees

• Current Assignee: Critikon Co. LLC
• Original Assignee: Johnson & Johnson Medical Incorporated (Johnson & Johnson)
• Inventors: Wells, Charles A., Medero, Richard, Hood, Rush W. Jr.
• Primary Examiner(s): Lacyk, John P.
• Application Number:
  US08/368,418
• Time in Patent Office: 1,028 Days
• Field of Search: 128/672, 128/677, 128/680-3
• US Class Current: 600/495
• CPC Class Codes: A61B 5/02116 of pulse wave amplitude A61B5/02225 takes precedence
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02225 using the oscillometric method

Abstract

An automated sphygmo-manometer which digitizes the pressure transducer output with sufficient resolution to preserve the details of the measured oscillation complexes. The "composite" arterial pulse signal containing the DC pressure component and the oscillation complexes is processed in a single processing channel so that the amplitudes of the oscillation pulse can be measured in the presence of the static components. Any necessary filtering is performed in the digital domain using known digital signal processing (DSP) techniques. In addition, dither signals may be added to the arterial pulse signal in the single processing channel in order to increase the apparent resolution. A simple finite impulse response (FIR) filter is used to sum respective samples to form high resolution samples from a plurality of low resolution samples. The FIR filter has zero crossings at the summing frequencies for the dither signal so as to eliminate the dither signal from the high resolution sum signal prior to determining the blood pressure from the composite signal using pulse separation and blood pressure calculation software.

Claims

1. An automated sphygmomanometer apparatus, comprising:

an inflatable and deflatable pressure cuff;

inflating means operatively coupled to said cuff for selectively applying a medium under pressure to said cuff for inflating and pressurizing said cuff;

cuff pressure sensing means coupled to said cuff for sensing cuff pressure and outputting a composite cuff pressure signal including said cuff pressure and any blood pressure oscillations therein;

deflating means operatively coupled to said cuff for selectively relieving pressure from said cuff;

a dither signal source which provides a substantially constant amplitude dither signal at a substantially constant dither frequency;

means for summing said dither signal with said composite cuff pressure signal to produce a dithered composite cuff pressure signal;

an A/D converter which digitizes said dithered composite cuff pressure signal and provides an A/D converted output signal;

a finite impulse response filter which sums respective samples of said A/D converted output signal over a predetermined time period to form a high resolution sum signal and which has zero crossings at said dither frequency so as to eliminate said dither signal from said sum signal;

means responsive to said sum signal from said finite impulse response filter for digitally separating a first signal representing said cuff pressure from a second signal representing said blood pressure oscillations; and

control means for controlling said inflating means to inflate said cuff and said deflating means to deflate said cuff during respective blood pressure determinations and for determining a blood pressure of a patient from said first and second signals.

2. An apparatus as in claim 1, wherein said dither frequency corresponds to an integral number of cycles of said predetermined time period.

3. A method of determining a patient'"'"'s blood pressure using an automatic oscillometric blood pressure monitor comprising a pressurized cuff, means for inflating and deflating said cuff, means for measuring arterial pressure oscillation complexes through measurement of time varying pressures within said cuff, and means for determining a patient'"'"'s blood pressure at predetermined measurement intervals by instructing said inflating and deflating means to inflate said cuff about an artery of the patient until said cuff is at a pressure level above the patient'"'"'s estimated systolic pressure and to deflate said cuff by predetermined pressure decrements, by searching for arterial pressure oscillation complexes at each pressure level, and by determining, from said arterial pressure oscillation complexes, said patient'"'"'s blood pressure, said method of determining a patient'"'"'s blood pressure comprising the steps of:

inflating a pressure cuff about an appendage of a patient to a pressure above the patient'"'"'s systolic pressure;

incrementally deflating said pressure cuff in predetermined pressure increments and outputting a composite cuff pressure signal at each pressure level, said composite cuff pressure signal including a cuff pressure signal and a blood pressure oscillation signal;

summing a substantially constant amplitude dither signal at a substantially constant dither frequency with said composite cuff pressure signal to create a dithered composite cuff pressure signal;

digitizing said dithered composite cuff pressure signal using an A/D converter and providing a digitized output signal;

summing respective samples of said digitized output signal over a predetermined time period to form a hiqh resolution sum signal using a finite impulse response filter having zero crossings at said dither frequency so as to eliminate said dither signal from said sum signal;

digitally separating said cuff pressure signal in said sum signal from said blood pressure oscillation signal in said sum signal; and

determining a blood pressure of said patient from said cuff pressure signal and said blood pressure oscillation signal.

4. An automated sphygmomanometer apparatus, comprising:

an inflatable and deflatable pressure cuff;

an inflate valve operatively coupled to said cuff which selectively applies a medium under pressure to said cuff for inflating and pressurizing said cuff;

a pressure transducer coupled to said cuff which senses cuff pressure and outputs a composite cuff pressure signal including said cuff pressure and any blood pressure oscillations therein;

a deflate valve operatively coupled to said cuff which selectively relieves pressure from said cuff;

a dither signal source which provides a substantially constant amplitude dither signal at a substantially constant dither frequency;

a summer which sums said dither signal with said composite cuff pressure signal to produce a dithered composite cuff pressure signal;

an A/D converter which digitizes said dithered composite cuff pressure signal and provides an A/D converted output signal;

a finite impulse response filter which sums respective samples of said A/D converted output signal over a predetermined time period to form a high resolution sum signal and which has zero crossings at said dither frequency so as to eliminate said dither signal from said sum signal; and

a microprocessor which is programmed so as to digitally separate a first signal representing said cuff pressure in said sum signal from a second signal representing said blood pressure oscillations in said sum signal, programmed so as to control said inflate valve to inflate said cuff and said deflate valve to deflate said cuff during respective blood pressure determinations, and programmed so as to determine a blood pressure of a patient from said first and second signals.