Improved method and apparatus for detecting optical pulses

Claim 1

A method for calculating the amount of a blood constituent from the blood flow charac­teristics of a patient by detecting an absorption signal corresponding to the absorption of light measured at two or more wavelengths in the patient's tissue including periodic changes in amplitude caused by periodic arterial pulses in the blood flow charac­teristics related to the patient's heartbeat and aperiodic changes in amplitude unrelated to the patient's heartbeat, characterized by, for each of the measured wavelengths: obtaining a time-measure of the absorption signal including periodic information and aperiodic information; processing the time-measure collec­tively to determine a composite waveform having a relative maximum and minimum amplitude corresponding to a composite periodic waveform of the periodic information in the time-measure so that the aperiodic information present in the time-measure is attenuated and filtered from the composite; and thereafter calculating the amount of blood con­stituent from the relative maximum and minimum ampli­tude of the composite periodic waveforms of the detected wavelengths.

Claim 2

A method for calculating the amount of a blood constituent from the blood flow charac­teristics of a patient by detecting an absorption signal corresponding to the absorption of light measured at two or more wavelengths in the patient's tissue including periodic changes in amplitude caused by periodic arterial pulses in the blood flow charac­teristics related to the patient's heartbeat and aperiodic changes in amplitude unrelated to the patient's heartbeat, characterized by, for each of the measured wavelengths: obtaining a time-measure of the absorption signal including periodic information and aperiodic information; processing the time-measure collec­tively to determine a composite waveform having a relative maximum and minimum amplitude corresponding to a composite periodic waveform of the periodic information in the time-measure so that the aperiodic information present in the time-measure is attenuated and filtered from the composite; and thereafter calculating the amount of blood con­stituent from the relative maximum and minimum ampli­tude of the composite periodic waveforms of the detected wavelengths.

Claim 8

The method of claims 2 to 6, characterized in that the absorption signal includes two wavelengths, further characterized in that collecting the time­measure is further characterized by converting the absorption signals for each of the wavelengths into digital data; collecting a first predetermined number of digitized data points for each of the wave­lengths of the absorption signal; forming a complex data set wherein one of the wavelengths data correspond to the real component and the other of the wavelengths data cor­respond to the imaginary component; determining the background absorption signal corresponding to the zero frequency component from the complex data set and subtracting the deter­mined background absorption component from the com­plex data set, thereby forming a modified data set; decimating the modified data set in time into a second predetermined number of samples; processing the second predetermined number of samples using a function selected from among the group comprising Hamming windows and simi­lar artifact reduction window functions, thereby forming a processed data set; Fourier transforming the processed data set into the frequency domain; determining the spectral components of the first and second wavelengths at the funda­mental frequency for the first pretermined number of heartbeats in the time sample from the transform; and determining the relative maximum and minimum amplitudes for the first and second wave­lengths using the amplitude of the zero frequency and fundamental frequency spectral components.

Claim 9

The method of claims 3 to 7 further charac­terized by determining the time of the occurrence of a heartbeat from the patient's ECG signal, and sampling the time-measure of the absorption signal to obtain a second predetermined number of samples per heartbeat, based on the determined time of occurrence of the heartbeats for each of the predetermined number of heartbeats in the time-­measure.

Claim 10

An apparatus for calculating the amount of a blood constituent from a photoelectri­cally detected absorption signal corresponding to the absorption of light measured at two or more wavelengths in a patient's tissue, including periodic changes in amplitude caused by periodic arterial pulses in the blood flow characteristics that are related to the patient's heartbeat, and including aperiodic changes in amplitude unrelated to the patient's heartbeat, and including a means for receiving the photoelectrically detected absorption signals of each of the measured wavelengths charac­terized by: means for obtaining a time-measure of the detected absorption signals including periodic information and aperiodic information; means for processing the obtained time-measures collectively to determine a composite waveform having a relative maximum and minimum am­plitude corresponding to a composite periodic wave­form of the periodic information in the time-measure so that the aperiodic information present in the time-measure is attenuated and filtered from the composite, and means for calculating the amount of blood constituent from the relative maximum and minimum amplitude of the composite periodic wave­forms of the detected wavelengths.

Claim 11

An apparatus for calculating the amount of a blood constituent from a photoelectri­cally detected absorption signal corresponding to the absorption of light measured at two or more wavelengths in a patient's tissue, including periodic changes in amplitude caused by periodic arterial pulses in the blood flow characteristics that are related to the patient's heartbeat, and including aperiodic changes in amplitude unrelated to the patient's heartbeat, and including a means for receiving the photoelectrically detected absorption signals of each of the measured wavelengths charac­terized by: means for obtaining a time-measure of the detected absorption signals including periodic information and aperiodic information; means for processing the obtained time-measures collectively to determine a composite waveform having a relative maximum and minimum am­plitude corresponding to a composite periodic wave­form of the periodic information in the time-measure so that the aperiodic information present in the time-measure is attenuated and filtered from the composite, and means for calculating the amount of blood constituent from the relative maximum and minimum amplitude of the composite periodic wave­forms of the detected wavelengths.

Claim 17

The apparatus of claims 10 to 14 characterized in that the absorption signal has two wavelengths, and the means for collecting the time-measure is further characterized by: means for converting the analog absorption signals for each of the wavelengths into digital data; means for collecting a first pre­determined number of digitized data points for each of the wavelengths of the absorption signal; first processor means for forming a complex data set wherein one of the wavelengths data correspond to the real component and the other of the wavelengths data correspond to the imaginary component; second processor means for deter­mining the background absorption signal corresponding to the zero frequency component from the complex data set and subtracting the determined background absorption component from the complex data set, thereby forming a modified data set; means for decimating the modified data set in time into a second predetermined number of samples; third processing means for processing the second predetermined number of samples using Hamming Window functions, thereby forming a pro­cessed data set; means for Fourier transforming the processed data set into the frequency domain; means for determining the spectral components of the first and second wavelengths at the fundamental frequency for the first predeter­mined number of heartbeats in the time sample from the transform; and means for determining the relative maximum and minimum amplitudes for the first and second wavelengths using the amplitude of the zero frequency and fundamental frequency spectral com­ponents.