Respiration estimation method and apparatus

A respiration estimation apparatus comprising:

• an R-wave amplitude detection circuit which detects an amplitude of an R wave from a cardiac potential waveform of a subject;
• an R-R interval detection circuit which detects an R-R interval as an interval between an R wave and an immediately preceding R wave from the cardiac potential waveform of the subject;
• an acceleration displacement detection circuit which detects an angular displacement of an acceleration vector at a chest of the subject from a triaxial acceleration signal caused by a respiratory motion of the subject;
• a processor which Fourier-transforms each of a time-series signal of the R-wave amplitude over time, a time-series signal of the R-R interval over time, and a time-series signal of the angular displacement over time to obtain a frequency spectrum of each of the signals of the R-wave amplitude, the R-R interval, and the angular displacement;
• and
• a signal selection circuit, wherein the signal selection circuit includes:
• a first detection circuit which extracts a peak frequency from each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, as candidates of the respiration frequency of the subject,
• a second detection circuit which detects a full width at half maximum of the peak frequency detected by the first detection circuit, for each of the frequency spectrum of the R-wave amplitude, the frequency spectrum of the R-R interval, and the frequency spectrum of the angular displacement, and
• a frequency selection circuit which selects, as the respiration frequency of the subject, a peak frequency at which the full width at half maximum extracted by the second detection circuit is not larger than a predetermined threshold taken from a memory among the three peak frequencies detected by the first detection circuit,
• wherein when there are a plurality of peak frequencies at which the full width at half maximum is not larger than the predetermined threshold, the frequency selection circuit selects, as the respiration frequency, the peak frequency at which the full width at half maximum is the narrowest of all the peak frequencies, the signal selection circuit further being configured to display a respiration frequency signal representing the respiration frequency of the subject over time;
• and when all the three full widths at half maximum exceed the predetermined threshold, the frequency selection circuit determines that data including the cardiac potential waveform and the triaxial acceleration signal is defective.