Blood pressure measurement apparatus

• US 4,768,519 A
• Filed: 05/15/1986
• Issued: 09/06/1988
• Est. Priority Date: 05/16/1985
• Status: Expired due to Fees

• Current Assignee: Terumo Kabushiki Kaisha T
• Original Assignee: Terumo Corporation
• Inventors: Yamaguchi, Keiji
• Primary Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/863,421
• Time in Patent Office: 845 Days
• Field of Search: 128/680-683, 364/415, 364/417
• US Class Current: 600/493
• CPC Class Codes: A61B 7/045 Detection of Korotkoff sounds A61B5/0225 takes precedence; measuring blood pressure A61B5/021

Abstract

Disclosed is a blood pressure measurement apparatus in which a waveform discrimination method is used in the recognition of Korotkoff sounds in the measurement of blood pressure by auscultation. In processing executed by the apparatus, the minimum point or maximum point (C3) of a signal waveform indicative of the sound of vibration produced by a blood vessel is detected, and a maximum value or minimum value point (C2) is detected within a predetermined time region (t₁) the final instant of which is the point (C3). If a level difference between the point (C2) and the point (C3) is within a predetermined range, there is detected a minimum value or maximum value point (C1) within a predetermined time region (t₂) the final instant of which is (C2). If a level difference between the point (C1) and the point (C2) is within a predetermined range, there is detected a maximum value or minimum value point (C4) within a predetermined time region (t₃) the starting instant of which is the point (C3). It is then discriminated whether a level difference between the point (C4) and the point (C3) falls within a predetermined range. Control proceeds in successive fashion when each of these conditions is satisfied, with a Korotkoff sound being recognized in the signal waveform when all of these conditions are satisfied.

Claims

1. A blood pressure measurement apparatus, comprising:

blood vessel information detecting means for detecting vibration of a blood vessel to produce a signal waveform;

storage means for storing the signal waveform produced by said blood vessel information detecting means and time information associated with the signal waveform;

reference absolute extreme value point locating means for operating on the signal waveform stored in said storage means in response to a conditional command to locate a reference absolute extreme value point of the signal waveform stored in said storage means, the reference extreme value point used as a base point for time duration measurement, said reference absolute extreme value point locating means comprising;

first extreme value detecting means for detecting one of first and next extreme value points in the signal waveform stored in said storage means;

polarity determining means for determining polarity of the one of the first and next extreme value points and for inverting a local portion of the signal waveform when the polarity is negative; and

means for providing as an output the reference absolute extreme value point representative of the one of the first and next extreme value points detected by said first extreme value detecting means;

C-point value searching means, responsive to the time information and to the output of said reference absolute extreme value point means, for finding relative extreme value points with respect to the reference extreme value point in the signal waveform stored in said storage means to thereby validate existence of a Korotkoff waveform, said C-point value searching means comprising;

means for receiving the local portion of the signal waveform stored in said storage means;

second extreme value detecting means for detecting the relative extreme value points in the local waveform portion in predeterined time intervals referenced to the reference absolute extreme value point in the signal waveform stored in said storage means, and for providing an occurrence output indicative thereof; and

level determining means for determining whether level differences between adjacent ones of the reference absolute and relative extreme value points fall within predetermined ranges and for providing level difference outputs indicative thereof; and

control means, responsive to said seocnd extreme value detecting means and said level determining means, for providing the conditional command to said reference absolute extreme value point locating means to detect the next extreme value point when the occurrence and level difference outputs indicate absence of at least one of occurrence and level differences within the predetermined ranges and for providing an output indicative of the existence of a Korotkoff sound waveform when the occurrence and level difference outputs indicate both occurrence and level differences within the predetermined ranges.

2. An apparatus according to claim 1, wherein said blood vessel information detecting means includes setting means for setting a threshold value for detection of the vibration of the blood vessel in accordance with the magnitude of the representation of a Korotkoff sound recognized immediately before.

3. An apparatus according to claim 1, wherein said storage means periodically stores a portion of the signal waveform using a predetermined time period.

4. A blood pressure measurement method, comprising the steps of:

(a) detecting vibration of a blood vessel to produce a signal waveform;

(b) storing the signal waveform produced in step (a) together with time information associated therewith;

(c) operating on the signal waveform stored in step (b) in response to a conditional command to locate a reference absolute extreme value point of the signal waveform, the reference extreme value point being used as a base point for time duration measurement, step (c) comprising the steps of;

(ci) detecting one of first and next extreme value points in the signal waveform stored in step (b);

(cii) determining polarity of the one of the first and next extreme value points and inverting a local portion of the signal waveform when the polarity is negative; and

(ciii) providing the reference absolute extreme value point representative of the one of the first and next extreme value points detected in step (ci);

(d) finding relative extreme value points with respect to the reference extreme value point and the time information to validate existence of a Korotkoff waveform, comprising the steps of;

(di) receiving the local portion of the signal waveform;

(dii) detecting the relative extreme value points in the local waveform portion in predetermined time intervals referenced to the reference absolute extreme value point in the signal waveform stored in step (b) and providing an occurrence output indicative thereof; and

(diii) determining whether level differences between adjacent ones of the reference absolute and relative extreme value points fall within predetermined ranges and providing level difference outputs indicative thereof;

(e) providing the conditional command for step (c) to detect the next extreme value point when the occurrence and level difference outputs indicate absence of at least one of occurrence and level differences within the predetermined ranges; and

(f) providing an output indicative of the existence of a Korotkoff sound waveform when the occurrence and level difference outputs indicate both occurrence and level differences within the predetermined ranges.