PULSE DETECTOR

• US 20120220881A1
• Filed: 02/21/2012
• Published: 08/30/2012
• Est. Priority Date: 02/28/2011
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: TAKAHASHI, Yusuke
• Granted Patent: US 9,044,206 B2
• Time in Patent Office: Days
• US Class Current: 600/483
• 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 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• 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

Abstract

A pulse detector (100) includes a pulse wave sensor (10); a pulse wave signal filtering section (200) having a first adaptive filter (202a) and second adaptive filter (202b), and an adaptive filter switching section (17); and a pulse wave frequency analyzer (400), wherein the adaptive filter switching section (17) starts an adaptive processing of the second adaptive filter (202b) at a first time point partway through a second interval in which the first adaptive filter (202a) is continuously carrying out adaptive processing, where the second interval occurs in the first interval, and switches from the first adaptive filter (202a) to the second adaptive filter (202b) at a second time point, which is a time point after the first time point and which is the end point of the second interval.

Claims

1. A pulse detector that detects a pulse signal that originates from a pulse of a subject, the pulse detector, comprising:

a pulse wave sensor that outputs a pulse wave signal in which are intermixed the pulse signal and a noise signal including a body movement noise signal originating in the body movement of the subject;

a pulse wave signal filtering section having a first adaptive filter and a second adaptive filter that self-adaptively adjusts a frequency response characteristic, the first and second adaptive filters being filters that filters the pulse wave signal, and an adaptive filter switching section that switches the adaptive filter to be used, where the switching occurs in a first interval in which the pulse wave sensor is continuously operating; and

a pulse wave frequency analyzer that performs a frequency analysis process at predetermined time intervals on the basis of a filtered signal outputted from the pulse wave signal filtering section and identifying a pulse-presenting spectrum that shows the pulse signal, wherein

at a first time point partway through a second interval in which the first adaptive filter is continuously carrying out adaptive processing, where the second interval occurs in the first interval, the adaptive filter switching section causes the second adaptive filter to start adaptive processing, and switches from the first adaptive filter to the second adaptive filter at a second time point that is a time point after the first time point and is the end point of the second interval.

2. The pulse detector according to claim 1, wherein

when the adaptive processing of the second adaptive filter is started, the adaptive filter switching section starts the adaptive processing from a state in which a filter coefficient has been initialized, or a state in which the filter coefficient has been set to a filter coefficient value of a time point in an interval in which the second adaptive filter had been operating continuously in the past.

3. The pulse detector according to claim 1, wherein

the adaptive filter switching section has an adaptive filter performance evaluation section that evaluates the performance of the first adaptive filter;

and

the first time point is a time point at which the performance of the first adaptive filter is evaluated to have degraded by the adaptive filter performance evaluation section.

4. The pulse detector according to claim 3, wherein

the adaptive filter performance evaluation section evaluates the performance of the first adaptive filter on the basis of an index calculated on the basis of a frequency spectrum of at least one signal among the pulse wave signal prior to filtering by the pulse wave signal filtering section and the filtered signal outputted from the pulse wave signal filtering section.

5. The pulse detector according to claim 4, wherein

the index is an index obtained by using the total value of the frequency spectrum appearing in the entire observed frequency band to divide the total of the value of the pulse-presenting spectrum and the value for each of the left and right spectra appearing adjacent to the pulse-presenting spectrum on the frequency axis;

and

the adaptive filter performance evaluation section evaluates the performance of the first adaptive filter by comparing a first value of the index obtained on the basis of the pulse wave signal before filtering by the pulse wave signal filtering section, and a second value of the index obtained on the basis of the filtered signal outputted from the pulse wave signal filtering section.

6. The pulse detector according to claim 1, wherein

the second time point is a time point at which a predetermined time has elapsed from the first time point.

7. The pulse detector according to claim 1, wherein

the second time point is a time point at which a predetermined permissible time has elapsed from a third time point, which is the time point at which the second interval started.

8. The pulse detector according to claim 1, wherein

the pulse wave signal filtering section includes

a delay processor that delays the pulse wave signal by a predetermined time, a filter coefficient update section that updates the coefficient of at least one of the first adaptive filter and the second adaptive filter, and a subtractor;

at least one of the first adaptive filter and the second adaptive filter outputs a first signal having high autocorrelation from among the output signals of the delay processor;

the subtractor subtracts the first signal from the pulse wave signal, generates a second signal having lower autocorrelation than the first signal, and feeds the second signal to the filter coefficient update section; and

the filter coefficient update section updates the coefficient of at least one of the first adaptive filter and the second adaptive filter so that the second signal is suppressed.