Method and apparatus for processing a physiological signal

• US 6,647,280 B2
• Filed: 01/14/2002
• Issued: 11/11/2003
• Est. Priority Date: 09/30/1999
• Status: Expired due to Term

• Current Assignee: Prothia
• Original Assignee: OB Scientific Incorporated
• Inventors: Bahr, Dennis E., Reuss., James L.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): Kremer, Matthew J
• Application Number:
  US10/047,356
• Publication Number:
  US 20020099281A1
• Time in Patent Office: 666 Days
• Field of Search: 702/75-76, 704/214, 704/208, 704/207, 600/309-310, 600/336, 600/323, 600/330, 600/473, 600/476
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/1464 specially adapted for foetal tissue
• CPC Class Codes: A61B 5/7257 using Fourier transforms

Abstract

A signal processing method, preferably for extracting a fundamental period from a noisy, low-frequency signal, is disclosed. The signal processing method generally comprises calculating a numerical transform for a number of selected periods by multiplying signal data by discrete points of a sine and a cosine wave of varying period and summing the results. The period of the sine and cosine waves are preferably selected to have a period substantially equivalent to the period of interest when performing the transform.

Claims

1. A method of signal processing for filtering noise from an input signal, wherein the input signal is noisy, the method comprising the following steps:

(a) calculating a numerical transform of the input signal to determine a fundamental period, wherein the numerical transform is calculated at each of a plurality of incremental periods by multiplying samples of the input signal by first and second periodic orthogonal waveforms of period equal to the selected incremental period;

(b) indexing through a buffer storing the first periodic waveform and a buffer storing the second periodic waveform, where the index is inversely proportional to a selected period to selectively decimate the length of the period;

(c) scaling and summing the calculated numerical transforms for a given incremental period to yield the fundamental period in the input signal; and

(d) utilizing the fundamental period for filtering noise from the input signal.

2. The method as defined in claim 1, further comprising the step of calculating an ensemble average to reconstruct the input signal.

3. The method as defined in claim 1, further comprising the step of calculating the power spectrum for each transform creating a power versus period buffer.

4. The method as defined in claim 3, further comprising the step of tracking a period of interest in the input signal through time by locating and tracking its peak in the power versus period buffer.

5. The method as defined in claim 1, wherein the input signal is a plethysmographic wave.

6. The method as defined in claim 1, wherein the input signal is a plethysmographic signal from a pulse oximetery sensor.

7. The method as defined in claim 1, wherein the input signal is a plethysmographic signal from a fetal pulse oximeter.

8. The method as defined in claim 1, wherein the input signal is slid through the transform such that a new data point is added and an old data point is subtracted for each iteration.

9. New The method as defined in claim 1, wherein the input signal is a physiological signal.

10. The method as defined in claim 1, wherein the input signal contains a dominant frequency of up to tens of hertz with intermittent broad band noise, wherein the frequency range of the broad band noise has a broad band noise period range in the same period range as the fundamental period.