Method and apparatus for removing artifact encountered during automatic blood pressure measurements

• US 5,542,428 A
• Filed: 03/23/1995
• Issued: 08/06/1996
• Est. Priority Date: 03/23/1995
• Status: Expired due to Fees

• Current Assignee: Spacelabs Medical Incorporated (OSI Systems Incorporated)
• Original Assignee: Spacelabs Medical Incorporated (OSI Systems Incorporated)
• Inventors: Jayne, Cynthia P.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/409,512
• Time in Patent Office: 502 Days
• Field of Search: 128/672, 128/677-683, 128/687
• US Class Current: 600/494
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence

Abstract

A blood pressure monitoring system having a blood pressure cuff, an air pump applying pressurized air to the cuff; a valve to selectively vent the cuff, and a pressure transducer generating a signal indicative of the pressure in the cuff corresponding to an occlusive pressure exerted by the cuff on an artery and a transient fluid pressure in the cuff indicative of the amplitude of an oscillometric pulse. An analog-to-digital converter connected to the transducer samples the output of the transducer and generates respective digital samples corresponding to the output of the transducer. A processor receives the respective digital samples corresponding to the signal indicative of the steady state fluid pressure in the cuff and the signal corresponding to the amplitude of the oscillometric pulses. The processor also records in a table the steady state fluid pressure at which each measurement is made and the amplitude of the peak oscillometric pulses at such pressure. The processor also determines all local maxima of the amplitude of the oscillometric peaks in the table, and examines the longest sequences of the amplitudes of the oscillometric peaks at cuff pressures adjacent to the cuff pressure at which each of the local maxima was obtained. Then, the processor chooses one of the local maxima as a true maximum value based on a comparison of the longest sequences adjacent to each of the local maxima and computes blood pressure using this value.

Claims

1. A blood pressure monitor, comprising:

a blood pressure cuff;

an air pump in fluid communication with said blood pressure cuff to direct pressurized air into said cuff;

a valve in fluid communication with said blood pressure cuff to selectively vent said cuff to atmosphere;

a pressure transducer in fluid communication with said blood pressure cuff, said pressure transducer generating a signal indicative of a steady state fluid pressure in said blood pressure cuff corresponding to an occlusive pressure exerted by said blood pressure cuff on an artery and a transient fluid pressure in said blood pressure cuff indicative of the amplitude of an oscillometric pulse;

an analog-to-digital converter connected to said pressure transducer for sampling the output of said pressure transducer and generating respective digital samples corresponding to the output of said pressure transducer; and

a processor electrically connected to said air pump, said valve and said analog-to-digital converter, said processor receiving the respective digital samples corresponding to the signal indicative of the steady state fluid pressure in said blood pressure cuff and the amplitude of the oscillometric pulses, said processing device energizing said air pump to inflate said blood pressure cuff, selectively energizing said valve to reduce the steady state fluid pressure in said blood pressure cuff, recording in a table the steady state fluid pressure and the amplitude of a peak of the oscillometric pulses at such pressure, determining all local maxima of the oscillometric peaks in the table, determining the longest sequences of oscillometric peaks adjacent to each of the local maxima, selecting one of the local maxima as a true maximum value based on a comparison of the longest sequences of oscillometric peaks at cuff pressures adjacent to and above and below the cuff pressure at which each of the local maxima occurred; and

computing at least one of the diastolic blood pressure, the systolic blood pressure, and the mean blood pressure based on the true maximum value.

2. The blood pressure monitor of claim 1 wherein the determining of the longest sequences of oscillometric peaks adjacent to each of the local maxima by said processor comprises:

finding the longest sequence of oscillometric peaks having amplitudes that are in sequentially decreasing order taken at cuff pressures that increase from the cuff pressure at which the local maxima was obtained; and

finding the longest sequence of oscillometric peaks having amplitudes that are in sequentially decreasing order taken at cuff pressures that decrease from the cuff pressure at which the local maxima was obtained.

3. The blood pressure monitor of claim 2 wherein the selecting of the true maximum value by said processor comprises:

adding the number of the oscillometric peaks in the longest sequence of decreasing amplitudes taken at cuff pressures above the cuff pressure at which the local maxima was obtained with the number of oscillometric peaks in the longest sequence of decreasing amplitudes taken at cuff pressures below the cuff pressure at which the local maxima was obtained to determine a total number of oscillometric peaks for each maxima;

comparing the total number of oscillometric peaks for each maxima; and

choosing as the true maximum the maxima having the largest total number.

4. The blood pressure monitor of claim 1 wherein said processor further creates a modified table by discarding from the table of the peak oscillometric pulses all data except the local maxima chosen as the true maximum and the longest oscillometric peak sequences used to choose the local maxima as the true maximum.

5. The blood pressure monitor of claim 4 wherein the processor computes at least one of the diastolic blood pressure, the systolic blood pressure and the mean blood pressure using the modified table.

6. A method for using a blood pressure monitor of the type having a blood pressure cuff, an air pump in fluid communication with the cuff to direct pressurized air into the cuff, a valve in fluid communication with the cuff to selectively vent the cuff to atmosphere, a pressure transducer in fluid communication with said cuff generating an output including a pressure signal indicative of a steady state fluid pressure in the cuff corresponding to an occlusive pressure exerted by said cuff on an artery and a transient fluid pressure in said cuff indicative of an amplitude of an oscillometric pulse, a processor in electrical communication with said air pump and said valve for selectively energizing said air pump or valve to pressurize or depressurize said cuff, respectively, said method comprising:

setting the steady state fluid pressure in said cuff to an initial value;

selectively energizing the air valve to reduce the steady state fluid pressure in the cuff;

sampling the pressure signal output by said pressure transducer resulting from variations in the fluid pressure in the cuff caused by the oscillometric pressure pulses;

recording in a table the steady state fluid pressure at which each sample is taken and the amplitude of the peak oscillometric pressure pulses at such steady state fluid pressure;

determining all local maxima of the oscillometric peaks in the table;

determining the longest sequences of the oscillometric peaks at cuff pressures adjacent to and above and below the cuff pressure at which each of the local maxima occurred;

selecting one of the local maxima as a true maximum value based on a comparison of the longest sequences adjacent to each of the local maxima; and

computing at least one of the diastolic blood pressure, the systolic blood pressure, and the mean blood pressure based on the true maximum value.

7. The method of claim 6 wherein said step of determining the longest sequences adjacent to each of the local maxima comprises:

finding the longest sequence of oscillometric peaks having amplitudes that are in sequentially decreasing order taken at cuff pressures that increase from the cuff pressure at which the local maxima was obtained; and

finding the longest sequence of oscillometric peaks having amplitudes that are in sequentially decreasing order taken at cuff pressures that decrease from the cuff pressure at which the local maxima was obtained.

8. The method of claim 7 wherein said step of selecting the true maximum comprises:

adding the number of the oscillometric peaks in the longest sequence of decreasing amplitudes taken at cuff pressures above the cuff pressure at which the local maxima was obtained with the number of oscillometric peaks in the longest sequence of decreasing amplitudes taken at cuff pressures below the cuff pressure at which the local maxima was obtained to determine a total number of oscillometric peaks for each maxima;

comparing the total number of oscillometric peaks for each maxima; and

choosing as the true maximum the maxima having the largest total number.

9. The method of claim 6 wherein said method further comprises the step of:

creating a modified table by discarding from the table formed during said recording step all data except the local maxima chosen as the true maximum and the longest oscillometric peak sequences used to choose the local maxima as the true maximum.

10. The method of claim 9 wherein said computing step is performed using the modified table.

11. A blood pressure monitor, comprising:

a blood pressure cuff;

an air pump in fluid communication with said blood pressure cuff to direct pressurized air into said cuff;

a valve in fluid communication with said blood pressure cuff to selectively vent said cuff to atmosphere;

a pressure transducer in fluid communication with said blood pressure cuff, said pressure transducer generating a signal indicative of a steady state fluid pressure in said blood pressure cuff corresponding to an occlusive pressure exerted by said blood pressure cuff on an artery and a transient fluid pressure in said blood pressure cuff indicative of the amplitude of an oscillometric pulse;

a processor electrically connected to said air pump and said valve, said processor receiving the signal indicative of the steady state fluid pressure in said blood pressure cuff and the amplitude of the oscillometric pulses, said processor energizing said air pump to inflate said blood pressure cuff to an initial value, selectively energizing said valve to reduce the steady state fluid pressure in said blood pressure cuff to a plurality of pressures recording in a table the steady state fluid pressure and the amplitude of a peak of the oscillometric pulses at each pressure, determining all local maxima of the oscillometric peaks in the table, counting each of the oscillometric peaks in the longest sequence of decreasing amplitudes at cuff pressures above and below the cuff pressure at which the local maxima was obtained, adding each of the oscillometric peaks counted for the local maxima to determine a total number of peaks for each maxima, comparing the total number of peaks for each maxima, selecting one of the local maxima as a true maximum value by choosing the maxima having the largest total number of peaks, modifying the table by retaining from the table only the oscillometric peaks of the true maximum value and the peaks in the longest sequence of decreasing amplitudes at cuff pressures above and below the cuff pressure at which the local maxima was obtained, and computing at least one of the diastolic blood pressure, the systolic blood pressure and the mean blood pressure using the modified table.