Apparatus and method for measuring pulse rate

• US 7,438,688 B2
• Filed: 08/28/2006
• Issued: 10/21/2008
• Est. Priority Date: 08/26/2005
• Status: Active Grant

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Kobayashi, Naoki, Ito, Kazumasa, Miyata, Kenji
• Primary Examiner(s): Nasser, Jr.; Robert L.
• Assistant Examiner(s): Toth; Karen E
• Application Number:
  US11/510,616
• Publication Number:
  US 20070060827A1
• Time in Patent Office: 785 Days
• Field of Search: 600485-528
• US Class Current: 600/500
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: G01R 23/165 using filters

Abstract

In an apparatus adapted to measure a pulse rate of a subject, a plurality of band pass filters, each of which has a center frequency that is different from the others are provided. The band pass filters are connected in parallel to one another so as to be adapted to receive a first signal corresponding to a pulse wave of the subject and be operable to output a plurality of second signals each of which is obtained by filtering the first signal with each center frequency. A first processor is operable to obtain a fundamental frequency of the first signal. A selector is operable to select one of the second signals which is output from one of the band pass filters having such a center frequency that is closest to the fundamental frequency. A second processor is operable to calculate the pulse rate from the selected one of the second signals.

Claims

1. An apparatus, adapted to measure a pulse rate of a subject, comprising:

a plurality of band pass filters, each of which has a center frequency that is different from the others, the band pass filters being connected in parallel to one another so as to be adapted to receive a first signal corresponding to a pulse wave of the subject and be operable to output a plurality of second signals each of which is obtained by filtering the first signal with each center frequency;

a first processor, operable to obtain a fundamental frequency of the first signal;

a selector, operable to select one of the second signals which is output from one of the band pass filters having such a center frequency that is closest to the fundamental frequency; and

a second processor, operable to calculate the pulse rate from the selected one of the second signals.

2. The apparatus as set forth in claim 1, wherein:

the first processor is operable to perform a fast Fourier transform processing to obtain the fundamental frequency.

3. The apparatus as set forth in claim 2, wherein:

the first processor is operable to determine a frequency having a maximum amplitude as the fundamental frequency.

4. The apparatus as set forth in claim 1, wherein:

the second processor is operable to calculate the pulse rate on the basis of an interval between time points at which a voltage of the selected one of the second signals either decreases to zero or increases to zero.

5. The apparatus as set forth in claim 4, further comprising:

a sound generator, operable to generate a sound at every one of the time points.

6. The apparatus as set forth in claim 1, further comprising:

a noise separator, operable to separate noise superimposed on the first signal.

7. The apparatus as set forth in claim 6, wherein:

the first signal is at least one of a red light signal and an infrared light signal supplied from a pulse photometer.

8. A method for measuring a pulse rate of a subject, comprising:

providing a plurality of band pass filters, each of which has a center frequency that is different from the others, the band pass filters being connected in parallel to one another so as to be adapted to receive a first signal corresponding to a pulse wave of the subject and be operable to output a plurality of second signals each of which is obtained by filtering the first signal with each center frequency;

obtaining a fundamental frequency of the first signal;

selecting one of the second signals which is output from one of the band pass filters having such a center frequency that is closest to the fundamental frequency; and

calculating the pulse rate from the selected one of the second signals.

9. The method as set forth in claim 8, wherein:

a fast Fourier transform processing is performed to obtain the fundamental frequency.

10. The method as set forth in claim 9, wherein:

a frequency having a maximum amplitude which is obtained by the fast Fourier transform processing is determined as the fundamental frequency.

11. The method as set forth in claim 8, wherein:

the pulse rate is calculated on the basis of an interval between time points at which a voltage of the selected one of the second signals either decreases to zero or increases to zero.

12. The method as set forth in claim 11, further comprising:

generating a sound at every one of the time points.

13. The method as set forth in claim 8, further comprising:

separating noise superimposed on the first signal.

14. The method as set forth in claim 13, wherein:

the first signal is at least one of a red light signal and an infrared light signal supplied from a pulse photometer.