Method for enhancing pulse oximetry calculations in the presence of correlated artifacts

1. In an oximeter, a method for determining a physiological parameter in the presence of correlated artifact, comprising:

obtaining two digital waveforms, x and y, said waveforms being representative of the absorption of two wavelengths of electromagnetic energy received from a blood-perfused tissue, and wherein each of said waveforms comprises a component corresponding to a plethysmographic waveform and a component corresponding to the correlated artifact;

calculating a plurality of weighted difference waveforms of the form x−R*y, wherein R is a multiplier, by varying R over a range;

evaluating said plurality of weighted difference waveforms using a shape characteristic of said weighted difference waveform;

identifying a weighted difference waveform most closely representative of said plethysmographic waveform, using said evaluating;

identifying a weighted difference waveform most different from said plethysmographic waveform, using said evaluating;

determining a pleth-based physiological parameter using said waveform most closely representative of said plethysmographic waveform;

determining at least one artifact-based physiological parameter using said waveform most different from said plethysmographic waveform; and

rejecting other possible candidate values for said pleth-based physiological parameter using said artifact-based physiological parameter.

2. The method of claim 1 further comprising, prior to said calculating a plurality of weighted difference waveforms, processing said waveforms to emphasize at least one characteristic of a plethysmographic pulse shape that is different from a characteristic of the correlated artifact.

3. The method of claim 1 wherein said physiological parameter is a pulse rate.

4. The method of claim 1 wherein said physiological parameter is an oxygen saturation value.

5. The method of claim 1 wherein said other candidates for said pleth-based physiological parameter are determined by other means.

6. The method of claim 1 wherein said evaluating comprises evaluating said weighted difference waveforms over a time interval encompassing at least one pulse period.

7. The method of claim 1 wherein said rejecting is performed in a frequency domain.

8. The method of claim 7 wherein said rejecting comprises excluding the strongest one or more frequencies contained in said waveform most different from said plethysmographic waveform.

9. The method of claim 1 wherein said shape characteristic comprises a measure of the complexity of said digital signals.

10. The method of claim 1 wherein said shape characteristic comprises a measure of the skew of said weighted difference waveforms.

11. The method of claim 1 wherein said shape characteristic is a parameter selected from the group consisting of a measure of the degree of arrhythmia of said waveforms, a measure of the degree of similarity or correlation between said first and second electromagnetic radiation signals, a measure of the degree of motion artifact by obtaining a ratio of a current pulse amplitude to the long-term average pulse amplitude of said waveforms, a ratio of a current pulse amplitude to the previous pulse amplitude of said waveforms, and a ratio of a current pulse period to that of an average pulse period of said waveforms.

12. The method of claim 1 wherein said shape characteristic comprises a measure of the kurtosis of said weighted difference waveforms.

13. The method of claim 1 wherein said shape characteristic comprises a measure of the total absolute change between waveform samples, normalized by a pulse amplitude.

14. The method of claim 1 wherein said shape characteristic comprises a measure of the dicrotic notch.