Continuous noninvasive blood pressure measuring apparatus and method

• US 5,255,686 A
• Filed: 07/02/1992
• Issued: 10/26/1993
• Est. Priority Date: 07/04/1991
• Status: Expired due to Fees

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Ozawa, Hideo, Takeda, Sunao, Hyogo, Mitsushi, Nakae, Yoshinobu
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US07/907,795
• Time in Patent Office: 481 Days
• Field of Search: 128/677-686
• US Class Current: 600/494
• CPC Class Codes: A61B 5/0225 the pressure being controlled by electric signals, e.g. derived from Korotkoff sounds

Abstract

In a continuous noninvasive blood pressure measuring apparatus, a systolic pressure, diastolic pressure, and mean arterial pressure for calibration are measured according to the output of a pressure sensor, a cuff pressure is set lower than the diastolic pressure by a cuff pressure control section, and a reference pulse wave is obtained from the arithmetic means of a plurality of cuff pulse waves. A CPU calculates the peak value and the bottom value of the reference pulse wave, and a cuff pressure mean value corresponding to the D.C. component of the reference pulse wave, and further calculates coefficients which are used to allow the peak value, bottom value and cuff pressure mean value thus obtained to correspond to correspond to the systolic pressure, diastolic pressure, and mean arterial pressure, respectively. The CPU calculates according to the output of a temperature sensor a cuff pressure temperature compensation value for compensating for an amount of variation of the cuff pressure which varies with the temperature of the cuff. In addition, the CPU, while compensating the cuff pressure, which is read continuously, with the cuff pressure temperature compensation value, continuously calculates a blood pressure by utilizing the cuff pressure thus compensated, and the coefficients provided by the coefficient calculating section, and the cuff pulse waves read continuously.

Claims

1. A continuous noninvasive blood pressure measuring apparatus for use in measuring blood pressure of a subject, the apparatus comprising:

a cuff to be put on the subject;

cuff control means for controlling a pressure of said cuff;

pressure sensor means for detecting a pressure of said cuff and for outputting a plurality of cuff pulse waves representative thereof;

temperature sensor means for detecting a temperature of said cuff;

calibration and measurement means for calibrating said pressure of said cuff and measuring a systolic pressure, a diastolic pressure and a mean arterial pressure in accordance with an output of said pressure sensor means, wherein said systolic pressure, said diastolic pressure and said means arterial pressure are used for calibration;

reference pulse wave forming means for calculating an arithmetic means of a plurality of cuff pulse waves provided by said pressure sensor means to form a reference pulse wave and for calculating a peak value, a bottom value and a cuff pressure mean value corresponding to a continuous wave component of said reference pulse wave;

coefficient calculating means for calculating coefficients to cause correspondence between said peak value, said bottom value, said cuff pressure mean value, as calculated by said reference pulse wave forming means, with said systolic pressure, said diastolic pressure, and said mean arterial pressure, respectively, as calculated by said calibration measurement means;

cuff pressure temperature compensation value calculating means for calculating a cuff pressure temperature compensation value in accordance with an output of said temperature sensor means, said cuff pressure temperature compensating value for use in compensating for an amount of variation of said cuff pressure with variation in temperature of said cuff; and

a blood pressure calculating means for compensating said cuff pressure with said cuff pressure temperature compensation value calculated by said cuff pressure temperature compensation value calculating means, and for continuously calculating a blood pressure by utilizing said cuff pressure thus compensated, said coefficient calculated by said coefficient calculating section, and said plurality cuff pulse waves.

2. A method of measuring a continuous noninvasive blood pressure of a subject, said method comprising the steps of:

setting a cuff on the subject;

performing a calibration measurement including the steps of;

increasing a cuff pressure to higher than a systolic pressure;

calculating a systolic pressure SYS, a diastolic pressure DIA, and a mean arterial pressure MAP;

setting a cuff pressure to a predetermined value which is lower than said diastolic pressure;

reading a cuff pressure pulse wave ADP and obtaining an arithmetic mean of several cuff pulse waves to form a reference pulse wave ADP1;

detecting a peak value APEAK and a bottom value ABTM from said reference pulse value ADP1 and averaging a DC component ADC of cuff pressure to achieve a mean value AMEAN;

calculating coefficients CS, CD, and CM in such manner that said coefficient CS causes said peak value APEAK to correspond to a systolic pressure SYS, said coefficient CD to correspond to said bottom value BTM of a diastolic pressure DIA, and said coefficient CM to correspond to said means value AMEAN of said mean arterial pressure MAP;

converting said DC component ADC, said cuff pulse wave ADP, and a temperature T of an air in said cuff into digital signals;

calculating a cuff pressure temperature compensation value Δ

P, where

space="preserve" listing-type="equation">Δ

P=P.sub.o ×

(T-T.sub.o)/α

T.sub.o

where,

P_o is an initial cuff pressure and T_o is an internal cuff air temperature when said coefficient CS, CD and CM are obtained, and

α

is a parameter related to said cuff;

calculating a temperature-compensated mean arterial pressure MAPC from

space="preserve" listing-type="equation">MAPC=CM×

(ADC-Δ

P);

determining whether said cuff pulse wave ADP is a positive component more than zero or whether it is a minus component not more than zero;

when said cuff pulse wave ADP is a positive component more than zero, calculating a systolic blood pressure BP, where

space="preserve" listing-type="equation">BP=C.S×

AD.P+MAP.C,

when said cuff pulse wave ADP is a minus component not more than zero, calculating a diastolic blood pressure BP, where

space="preserve" listing-type="equation">BP=CD×

ADP+MAPC;

and

calculating a blood pressure waveform BPW by multiplying said cuff pulse wave ADP inputted continuously and a component of a temperature compensated cuff pressure using said coefficient CS, CD and CM.