Method and apparatus for estimating a physiological parameter
View Patent ↗A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The method and apparatus of the invention take into account the physical limitations on various physiological parameters being monitored when weighting and averaging a series of measurements. Varying weights are assigned different measurements, measurements are rejected, and the averaging period is adjusted according to the reliability of the measurements. Similarly, calculated values derived from analyzing the measurements are also assigned varying weights and averaged over adjustable periods. More specifically, a general class of filters such as, for example, Kalman filters, is employed in processing the measurements and calculated values. The filters use mathematical models which describe how the physiological parameters change in time, and how these parameters relate to measurement in a noisy environment. The filters adaptively modify a set of averaging weights to optimally estimate the physiological parameters.
1. A physiological monitor for monitoring a pulse rate of a living being, said monitor comprising a signal processor configured to:
perform a transformation on a time-domain plethysmograph waveform, to obtain a power spectrum having multiple peaks corresponding to a fundamental frequency and one or more harmonics of said fundamental frequency;
perform a calculation of a validity metric for said multiple peaks, wherein said validity metric is based in part on the strength of said fundamental frequency and said one or more harmonics; and
estimate a pulse rate using said calculation of said validity metric.
2. A physiological monitor for monitoring a patient's pulse rate using time-domain data corresponding to two wavelengths of electromagnetic energy transmitted through the tissue of the patient, said monitor comprising a signal processor configured to:
track the pulse rate in the data using an adaptive comb filter;
periodically calculate a frequency power spectrum of one of said wavelengths;
calculate an autocorrelation function of said wavelengths;
identify peaks in said frequency power spectrum and peaks in said autocorrelation function; and
estimate the pulse rate from said peaks in said frequency power spectrum and said peaks in said autocorrelation function using one or more rules.
3. The physiological monitor of claim 2 , wherein said one or more rules are configured for determining said pulse rate as corresponding to the frequency corresponding with a peak present in both said frequency power spectrum and said autocorrelation function.
4. The physiological monitor of claim 2 , wherein said processor is configured to calculate a frequency power spectrum using a Fourier transform.
5. The physiological monitor of claim 2 , wherein said processor is configured to use the frequency power spectrum to determine which of a plurality of peaks in the frequency power spectrum corresponds to the fundamental frequency.