Cepstral domain pulse oximetry

A method of determining a pulse rate of a patient from at least one time domain plethysmographic signal obtained from the patient, said method comprising the steps of:

• obtaining a time domain based estimate of the pulse rate of the patient from the time domain plethysmographic signal;
• transforming the time domain plethysmographic signal to a spectral domain plethysmographic signal;
• obtaining a spectral domain based estimate of the pulse rate of the patient from the spectral domain plethysmographic signal;
• transforming the spectral domain plethysmographic signal to a cepstral domain plethysmographic signal;
• obtaining a cepstral domain based estimate of the pulse rate of the patient from the cepstral domain plethysmographic signal;
• and
• determining a best estimate of the pulse rate of the patient based on at least the time, spectral, and cepstral domain based estimates of the pulse rate of the patient.

A pulse oximeter comprising:

• a first optical signal source operable to emit an optical signal characterized by a first wavelength;
• a second optical signal source operable to emit an optical signal characterized by a second wavelength different than said first wavelength;
• a drive system operable to cause operation of said first and second optical signal sources such that each of said first and second optical signal sources emit first and second optical signals, respectively, in accordance with a multiplexing method;
• a detector operable to receive said first and second optical signals after said first and second optical signals are attenuated by a patient tissue site of a patient, said detector being further operable to provide an analog detector output signal representative of said attenuated first and second optical signals;
• a digital sampler operable to sample the analog detector output signal at a desired sampling rate and output a digital signal having a series of sample values representative of said attenuated first and second optical signals;
• and
• a digital processor enabled to demultiplex the series of sample values into first and second time domain plethysmographic signals, transform the first and second time domain plethysmographic signals into first and second spectral domain signals, transform the first and second spectral domain plethysmographic signals into first and second cepstral domain plethysmographic signals, and examine the first and second cepstral domain plethysmographic signals to obtain information therefrom relating to a physiological condition of the patient.

A pulse arbitration method for use in determining a fundamental pulse frequency of a patient from multiple signal domains associated with at least one time domain plethysmographic signal obtained from the patient, said method comprising the steps of:

• transforming the time domain plethysmographic signal to a spectral domain plethysmographic signal;
• transforming the spectral domain plethysmographic signal to a cepstral domain plethysmographic signal;
• examining the spectral and cepstral domain plethysmographic signals to identify corresponding spectral and cepstral domain plethysmographic signal peaks;
• and
• using the identified corresponding spectral and cepstral domain plethysmographic signal peaks to select the fundamental pulse frequency from among a plurality of possible candidates for the fundamental pulse frequency of the patient.