Apparatus and method for measuring pulse waves

• US 8,758,259 B2
• Filed: 08/03/2009
• Issued: 06/24/2014
• Est. Priority Date: 09/26/2008
• Status: Expired due to Fees

• Current Assignee: TDK Corporation
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Suzuki, Takuji
• Primary Examiner(s): Mallari, Patricia
• Assistant Examiner(s): Ramachandran, Vasuda
• Application Number:
  US12/534,424
• Publication Number:
  US 20100081947A1
• Time in Patent Office: 1,786 Days
• Field of Search: 600/301, 600/509, 600500-507
• US Class Current: 600/500
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6892 Mats
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

Pulse waves of a subject are detected in time sequence. Amplitude of the pulse waves is detected, and an interval between two pulse waves adjacent along a time axis is detected. A first change ratio of the interval along the time axis, and a second change ratio of the amplitude divided by the interval along the time axis are calculated respectively. By comparing the first change ratio and the second change ratio with a first threshold and a second threshold respectively, it is decided whether the pulse waves of the subject are irregular.

Claims

1. An apparatus for measuring pulse waves, comprising:

a pulse wave detection unit configured to detect pulse waves of a subject;

an amplitude detection unit configured to detect a plurality of amplitudes of the pulse waves;

an interval detection unit configured to detect an interval of time between two of the pulse waves, the two being adjacent along a time axis; and

a decision unit configured to calculate a first change ratio and a second change ratio, compare the first change ratio with a first threshold, and, when the first change ratio is larger than the first threshold, decide whether the pulse waves represent arrhythmia by comparing the second change ratio with a second threshold, wherein

the first change ratio is a ratio of a difference between the interval and a previous interval to the previous interval,

the second change ratio is a ratio of a difference between the amplitude divided by the interval and a previous amplitude divided by the previous interval to the previous amplitude divided by the previous interval,

wherein the interval detection unit detects a maximum and a minimum of each pulse wave in a predetermined period along the time axis, calculates an internally dividing point between the maximum and the minimum at a predetermined ratio, detects a time at an intersecting point of the internally dividing point and each pulse wave, and calculates the interval as a difference between the time at the intersecting point and a time at a previous intersecting point, and

the amplitude detection unit calculates the amplitude as a difference between the maximum and the minimum.

2. The apparatus according to claim 1, wherein the predetermined ratio of the internally dividing point is above 0.64.

3. The apparatus according to claim 1, wherein the predetermined ratio of the internally dividing point is determined by a ratio of the maximum to a local maximum value in the pulse waves, measured previously.

4. The apparatus according to claim 1, wherein

the pulse waves detection unit differentiates the pulse waves along the time axis after detecting the pulse waves.

5. A method for measuring pulse waves, comprising:

detecting pulse waves of a subject;

detecting a plurality of amplitudes of the pulse waves;

detecting an interval of time between two of the pulse waves, the two being adjacent along a time axis;

calculating, using a processor, a first change ratio and a second change ratio, wherein

the first change ratio is a ratio of a difference between the interval and a previous interval to the previous interval,

the second change ratio is a ratio of a difference between the amplitude divided by the interval and a previous amplitude divided by the previous interval to the previous amplitude divided by the previous interval;

comparing the first change ratio with a first threshold; and

when the first change ratio is larger than the first threshold, deciding whether the pulse waves represent arrhythmia by comparing the second change ratio with a second threshold,

wherein a step of detecting the interval includes

detecting a maximum and a minimum of the pulse waves in a predetermined period along the time axis;

calculating an internally dividing point between the maximum and the minimum at a predetermined ratio;

detecting a time at an intersecting point of the internally dividing point and the pulse waves; and

calculating the interval as a difference between the time at the intersecting point and a time at a previous intersecting point; and

a step of detecting the plurality of amplitudes includes calculating the amplitude as a difference between the maximum and the minimum.