Method and apparatus for measuring pulse rate and oxygen saturation achieved during exercise

• US 8,649,837 B2
• Filed: 07/17/2008
• Issued: 02/11/2014
• Est. Priority Date: 07/19/2007
• Status: Active Grant

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Sugo, Yoshihiro, Kobayashi, Naoki, Takeda, Sunao
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Foreman, Jonathan M
• Application Number:
  US12/175,413
• Publication Number:
  US 20090024014A1
• Time in Patent Office: 2,035 Days
• Field of Search: 600/323, 600/324, 600/336, 600/502
• US Class Current: 600/323
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

In order to measure a pulse rate and an oxygen saturation of a subject who is in an exercised state, each of two pulse wave signals obtained from the subject is separated into a signal component and a noise component. A frequency spectrum of the signal component and a frequency spectrum of the noise component are obtained. It is judged whether a body motion of the subject is occurred based on the frequency spectrum of the signal component and the frequency spectrum of the noise component. A pulsation frequency is determined based on the judgment as to the body motion. The pulse rate is calculated based on the pulsation frequency. The oxygen saturation is calculated based on a ratio of spectra of the two pulse wave signals corresponding to the pulsation frequency.

Claims

1. A method of measuring a pulse rate and an oxygen saturation of a subject who is in an exercised state, comprising:

separating each of two pulse wave signals obtained from the subject into a signal component and a noise component;

obtaining a frequency spectrum of the signal component and a frequency spectrum of the noise component;

judging whether a body motion of the subject is occurred based on the frequency spectrum of the signal component and the frequency spectrum of the noise component;

determining a pulsation frequency based on the judgment as to the body motion;

calculating the pulse rate based on the pulsation frequency; and

calculating the oxygen saturation based on a ratio of spectra of the two pulse wave signals corresponding to the pulsation frequency.

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

the pulsation frequency is determined as a fundamental frequency of the signal component, when it is judged that the body motion is not occurred.

3. The method as set forth in claim 1, further comprising:

judging whether a first difference between a first frequency at which the frequency spectrum of the signal component has a maximum amplitude and a second frequency at which the frequency spectrum of the noise component has a maximum amplitude is no less than a first prescribed value, when it is judged that the body motion is occurred, wherein;

the pulsation frequency is determined as the first frequency when it is judged that the first difference is no less than the first prescribed value.

4. The method as set forth in claim 3, further comprising:

judging whether a second difference between the first frequency and one half of a third frequency which is higher than the first frequency and at which the frequency spectrum of the signal component has a peak is less than a second prescribed value, when it is judged that the first difference is less than the first prescribed value, wherein;

the pulsation frequency is determined as the first frequency when it is judged that the second difference is less than the second prescribed value.

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

judging whether a third difference between the one half of the third frequency and a fourth frequency at which the frequency spectrum of the signal component has a second-maximum amplitude is less than a third prescribed value, when the it is judged that the second difference is no less than the second prescribed value, wherein;

the pulsation frequency is determined as the fourth frequency when it is judged that the third difference is less than the third prescribed value.

6. The method as set forth in claim 5, further comprising:

judging whether a ratio of a previously-determined pulsation frequency to a fourth difference between the previously-determined pulsation frequency and the one half of the third frequency is less than a fourth prescribed value, when it is judged that the third difference is no less than the third prescribed value, wherein;

the pulsation frequency is determined as the one half of the third frequency when it is judged that the ratio is less than the fourth prescribed value.

7. An apparatus configured to measure a pulse rate and an oxygen saturation of a subject who is in an exercised state, comprising:

a separator, configured to separate each of two pulse wave signals obtained from the subject into a signal component and a noise component;

a spectra obtainer, configured to obtain a frequency spectrum of the signal component and a frequency spectrum of the noise component;

a judge, configured to judge whether a body motion of the subject is occurred based on the frequency spectrum of the signal component and the frequency spectrum of the noise component;

a pulsation frequency determinant, configured to determine a pulsation frequency based on the judgment as to the body motion;

a pulse rate calculator, configured to calculate the pulse rate based on the pulsation frequency; and

an oxygen saturation calculator, configured to calculate the oxygen saturation based on a ratio of spectra of the two pulse wave signals corresponding to the pulsation frequency.