SIGNAL PROCESSING APPARATUS
The present invention involves a method and an apparatus for analyzing measured signals, including the determination of a measurement of oxygen saturation and respiration rate in the measured signals during a calculation of a physiological parameter of a monitored patient. Use of this invention is described in particular detail with respect to oximetry-based measurements but extends to other types of measurements.
1 . A patient monitoring system configured to determine one or more physiological characteristics of a patient, the system comprising:
a plurality of light emitters configured to emit light of at least two different wavelengths into tissue of a patient;
a detector configured to detect the emitted light after attenuation by the tissue and output a signal indicative of the detected light; and
a processing system configured to receive and process the detected light and determine information indicative of oxygen saturation, pulse rate and respiration rate, the processing system configured to reduce an effect of motion noise by using at least a frequency domain calculation.
2 . The patient monitoring system of claim 1 , wherein the frequency domain calculation comprises a Fourier transform.
3 . The patient monitoring system of claim 1 , wherein the processing system is further configured to determining a plurality of ratios of values based on the at least two different wavelengths.
4 . The patient monitoring system of claim 1 , wherein the processing system is further configured to use at least a wavelet transform in the determination of at least a portion of the information.
5 . The patient monitoring system of claim 1 , wherein the information comprises a primary signal and a reference signal, the primary signal indicative of the oxygen saturation and the reference signal indicative of the respiration rate.
6 . A patient monitor configured to determine one or more physiological characteristics of a patient, the system comprising:
an input for receiving from a detector an indication of light of first and second wavelengths attenuated by body tissue carrying pulsing blood over a period of time;
a processor configured to receive and process the detected light and determine information indicative of oxygen saturation, pulse rate and respiration rate, the processing system configured determine at least a portion of the information using at least a frequency domain calculation.
7 . The patient monitor of claim 6 , wherein the frequency domain calculation comprises a Fourier transform.
8 . The patient monitor of claim 6 , wherein the processing system is further configured to determining a plurality of ratios of values based on the at least two different wavelengths.
9 . The patient monitor of claim 6 , wherein the processing system is further configured to use at least a wavelet transform in the determination of at least a portion of the information.
10 . The patient monitor of claim 6 , wherein the information comprises a primary signal and a reference signal, the primary signal indicative of the oxygen saturation and the reference signal indicative of the respiration rate.
11 . A method of determining a physiological parameter of a patient comprising:
supplying a control signal to alternately generate a light signal of at least a first wavelength and a second wavelength and at a modulation frequency higher than a rate of a physiological parameter of interest;
receiving an attenuated signal based on the light signal, the attenuated signal comprising a first component representing an ambient light signal and a second component representing the light signal of the first or second wavelength;
digitizing the attenuated signal to generate a digital signal;
processing the digital signal to generate a processed signal, said processing comprising transforming the digitized signal to the frequency domain and determining a physiological parameter of interest, the physiological parameter being a respiration rate.
12 . The method of claim 11 , wherein transforming the digitized signal to the frequency domain comprises using a Fourier transform.
13 . The method of claim 11 , further comprising using at least a wavelet transform to determine the parameter of interest.
14 . The method of claim 11 , further comprises determining a primary signal and a reference signal, the primary signal indicative of the oxygen saturation and the reference signal indicative of the respiration rate.