Method and apparatus for estimating a physiological parameter

• US 7,931,599 B2
• Filed: 03/01/2005
• Issued: 04/26/2011
• Est. Priority Date: 08/07/1995
• Status: Expired due to Term

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Yorkey, Thomas J., Baker, Clark R. Jr.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US11/070,629
• Publication Number:
  US 20050143634A1
• Time in Patent Office: 2,247 Days
• Field of Search: 600/300, 600/310, 600/322, 600/323, 600/324, 600/336, 600/481, 600/508, 600/509, 600/515, 600/502, 702/191, 702/192, 702/193, 702/194, 702/195, 702/196, 702/197
• US Class Current: 600/502
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• 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 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: H03H 21/003 KALMAN filters

Abstract

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.

Claims

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.