Surgery – Diagnostic testing – Cardiovascular
Patent
1998-11-04
2000-12-05
O'Connor, Cary
Surgery
Diagnostic testing
Cardiovascular
600485, A61B 500
Patent
active
061559830
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pulse wave detecting device for detecting pulse waves, and to a pulse measurer employing the aforementioned pulse wave detecting device.
2. Description of the Related Art
Pulse measurers which detect pulse waves, calculate the pulse rate, and then notify the user of the calculated result have been commercially available for some time. This type of pulse measurer calculates the pulse rate using the signals (pulse wave signals) output from a pulse wave detecting sensor that is disposed near a site on the user's body where the pulse measurement is to be made. Known methods for calculating the pulse rate include the rectangular wave processing method and frequency analysis method described below.
In the rectangular wave processing method, the pulse wave signal is converted to a rectangular wave, and the pulse rate is calculated by measuring the period of the rectangular wave (the pulse rate is proportional to the reciprocal of the period). In other words, the pulse rate can be calculated by investigating the variation in the level of the pulse wave signal over a time domain. Thus, this method enables calculation of the pulse rate by only a small amount of calculations and a small-scale circuit structure.
In the frequency analysis method, the pulse wave signal is subjected to frequency analysis, the spectral line having a maximal level is extracted from the spectrum obtained as a result of the frequency analysis, and the pulse rate is calculated from the frequency of this spectral line. In other words, the pulse rate is calculated by comparing the levels of the pulse wave signals within a frequency domain. FFT is typically employed as the frequency analysis method.
However, in addition to the pulse wave components, other noise may be superimposed on the output from the pulse wave detecting sensor. Since this superimposed noise is not necessarily regular, merely providing an analog filter at the input stage does not sufficiently remove its effects. Accordingly, the present inventors have proposed the following processes (1) through (3) for reducing such noise.
(1) Impulse noise removal processing
As used here, impulse noise is the general term for noise which is generated suddenly. An example of a pulse wave signal containing superimposed impulse noise is shown in FIG. 11. FIG. 11(a) shows the pulse wave signal in the time domain, while FIG. 11(b) shows the spectrum obtained after performing an FFT on this pulse wave signal. As is clear from the figures, due to the superimposition of impulse noise, the pulse wave signal is extremely deformed over the time period t1.about.t2 in FIG. 11(a), and a spectral line is present which is higher than spectral line SP which shows the fundamental wave of the pulse wave. As described above, in the frequency analysis method, the pulse rate is calculated based on the highest level spectral line. Thus, since frequency analysis is performed on the pulse wave signal containing the superimposed impulse noise as shown in the figure, it is not possible to accurately calculate the pulse rate.
Therefore, the present inventors proposed a device which monitors for the presence or absence of phenomena which cause impulse noise to be generated, and when, based on the results of this monitoring, there is a concern that impulse noise may be superimposed, performs frequency analysis after inserting a dummy signal in the interval containing the impulse noise in the pulse signal (for example, time period t1.about.t2 in FIG. 11(a)) (for details, see specification and figures accompanying Japanese Patent Application No. 273238 of 1995: Japanese Patent First Publication No. 113653 of 1997). In this device, because a dummy signal having a value of 0 is inserted in the time interval t1.about.t2 in which the impulse noise is superimposed, spectral line SP, which expresses the fundamental wave of the pulse wave, becomes the highest level spectral line in the spectrum obtained as a result of FFT processing. Note t
REFERENCES:
patent: 5868679 (1999-02-01), Miyazaki
patent: 5873834 (1999-02-01), Yanagi et al.
Kosuda Tsukasa
Nakamura Chiaki
Carter Ryan
O'Connor Cary
Seiko Epson Corporation
Seiko Instruments Inc.
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