Non-invasive blood pressure measurement device

• US 5,485,838 A
• Filed: 12/07/1993
• Issued: 01/23/1996
• Est. Priority Date: 12/07/1992
• Status: Expired due to Fees

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Yoshida, Tatsuo, Ukawa, Teiji
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): NASSER, ROBERT L
• Application Number:
  US08/162,254
• Time in Patent Office: 777 Days
• Field of Search: 128/633-634, 128/664-667, 128/670, 128/680, 128/681, 128/677, 128/672, 128/668, 356/41
• US Class Current: 600/330
• 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
• CPC Class Codes: A61B 5/02241 of small dimensions, e.g. adapted to fingers
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

A non-invasive blood pressure measurment device including: a cuff, a pressure detector for detecting a cuff pressure; a cuff pressure control pump for linearly increasing or decreasing the cuff pressure; a light-emitting member for injecting a beam of light into a part of a body by the cuff; light-receiving members for detecting an amount of light transmitted or an amount of light reflected of the beam of light injected into the body from the light-emitting member; a demodulating circuit for separating a pulsatile component from the light-receiving signal obtained from the light-receiving members; a CPU for sending a control signal to the cuff pressure control pump to thereby either increase the cuff pressure if it is judged that the pulsatile component has not been detected before applying pressure to the cuff based on the detection output from the demodulating circuit or decrease the once increased cuff pressure, and detecting an inflection point in the light-receiving signal in the course of increasing or decreasing the cuff pressure to thereby output a cuff pressure at the inflection point as a mean pressure value of a subject who is in systemic hypotension.

Claims

1. A non-invasive blood pressure measurement device comprising:

a cuff configured to be attached to a body part of a subject;

a pressure detector operatively connected to said cuff for detecting a cuff pressure applied to the body part by the cuff and outputting a detection output;

pressure applying means for applying pressure to the cuff in response to an input pressure increase control signal and for dropping the cuff pressure in response to an input pressure decrease control signal;

a light-emitting member for injecting beams of light of two different wavelengths, one being a beam of red light and the other being a beam of infrared light, into the body part of the subject to which pressure is applied by said cuff;

a light-receiving member for detecting one of amounts of light transmitted and amounts of light reflected of the beams of light injected into the body part from said light-emitting member, and thereby outputting light-receiving signals for the two different wavelengths;

signal component separating means operatively connected to said light-receiving member for separating a dc component and a pulsatile component from each of the light-receiving signals of the respective wavelengths obtained from said light-receiving member;

oxygen saturation calculating means for calculating a ratio of a pulsation component in absorption of one wavelength due to arterial blood flow to that of the other wavelength from the dc components and the pulsatile components of the respective wavelengths obtained from said signal component separating means, and for calculating an oxygen saturation from the ratio;

permissible range of variance calculating means for obtaining a mean value of oxygen saturation measurements of the subject before said pressure applying means applies pressure to the cuff, and for calculating a permissible range of variance from the mean value, the oxygen saturation measurements being obtained from said oxygen saturation calculating means;

cuff pressure control means for outputting the pressure increase control signal to said pressure applying means while receiving the detection output from said pressure detector, and for outputting the pressure decrease control signals, for dropping the once increased cuff pressure, to said pressure applying means, after the permissible range of variance has been obtained;

determining means for determining whether or not an oxygen saturation obtained in the course of increasing or decreasing the cuff pressure is within the permissible range of variance and for outputting a determination result; and

blood pressure measuring means for selecting, based on the determination result output by said determining means, a valid pulse wave signal from the pulsatile components obtained by said signal component separating means in the course of increasing or decreasing the cuff pressure and for calculating a blood pressure value of the subject by a volume oscillometric method from an amplitude of the valid pulse wave signal and the detection output obtained from said pressure detector.

2. A method for measuring blood pressure non-invasively, the method comprising the steps of:

injecting beams of light of two different wavelengths, one being a beam of red light and the other being a beam of infrared light, into a body part of a subject to which a cuff is attached;

detecting one of amounts of light transmitted and amounts of light reflected of the beams of light injected into the body part and outputting, for each of the two wavelengths, a resultant light-receiving signal;

separating a dc component and a pulsatile component from each of the light-receiving signals of the respective wavelengths;

calculating a ratio of a pulsation component in absorption of one wavelength due to arterial blood flow to that of the other wavelength from the dc components and the pulsatile components of the respective wavelengths;

calculating an oxygen saturation from the ratio;

obtaining a mean value of oxygen saturation measurement of the subject before applying pressure to the cuff;

calculating a permissible range of variance from the mean value;

increasing pressure to the cuff while detecting the cuff pressure, or decreasing the cuff pressure while detecting the cuff pressure, after the permissible range of variance is calculated;

determining whether or not an oxygen saturation obtained in the course of increasing or decreasing the cuff pressure is within the permissible range of variance and then outputting a determination result; and

selecting, based on the determination result, a valid pulse wave signal from the pulsatile components in the course of increasing or decreasing the cuff pressure;

calculating a blood pressure value of the subject by a volume oscillometric method from an amplitude of the valid pulse wave signal and the detected cuff pressure.