Method and apparatus for detecting optical pulses
First Claim
1. A method for calculating .[.the.]. .Iadd.an .Iaddend.amount of a blood constituent from the blood flow characteristics of a patient comprising:
- detecting an absorption signal corresponding to .[.the.]. absorption of light measured at two or more wavelengths in the patient'"'"'s tissue including periodic changes caused by periodic arterial pulses in the blood flow characteristics and aperiodic changes unrelated to the patient'"'"'s heartbeat;
detecting an ECG signal corresponding to the patient'"'"'s ECG waveform corresponding to the periodic electrical heart activity of the patient;
selecting a first time-measure of the absorption signal including a maximum and minimum amplitude change in absorption;
selecting a second time-measure of the ECG signal including components corresponding to the occurrence of the heartbeat;
correlating the ECG signal and the absorption signal by multiplying the first time-measure of the absorption signal and the second time-measure of the ECG signal together to form a waveform product and thereafter shifting the time-measure of the absorption signal backwards in time relative to the time-measure of the ECG signal and multiplying the shifted and unshifted waveforms together to identify a maximum waveform product corresponding to the product of the ECG signal corresponding to the occurrence of the heartbeat and the maximum amplitude of the absorption signal;
processing the absorption signal and the determined correlation to identify the periodic changes in the absorption signal associated with the determined maximum waveform product likely to correspond to arterial pulses in the patient'"'"'s blood flow characteristics; and
calculating the amount of the blood constituent from the identified periodic changes in the absorption signal.
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Accused Products
Abstract
A method and apparatus for improving the calculation of oxygen saturation and other blood constituents by non-invasive pulse oximeters. The method and apparatus permit more accurate determination of blood flow by collecting time-measures of the absorption signal at two or more wavelengths and processing the collected time-measure to obtain composite pulsatile flow data from which artifacts have been filtered. The processing may occur in the time domain or in the frequency domain. In the preferred time domain embodiment, successive portions of periodic information are weighted and added together in synchrony to obtain the composite pulse information. In the preferred frequency domain embodiment, the time-measure is Fourier transformed into its spectral components to form the composite information. A new method and apparatus for correlating the heartbeat and optical pulse is provided whereby a product of the ECG R-wave and optical pulse signals corresponding to the same heartbeat is obtained, and one signal is time shifted relative to the other until a maximum waveform product corresponding to the heartbeat is determined.
339 Citations
34 Claims
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1. A method for calculating .[.the.]. .Iadd.an .Iaddend.amount of a blood constituent from the blood flow characteristics of a patient comprising:
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detecting an absorption signal corresponding to .[.the.]. absorption of light measured at two or more wavelengths in the patient'"'"'s tissue including periodic changes caused by periodic arterial pulses in the blood flow characteristics and aperiodic changes unrelated to the patient'"'"'s heartbeat; detecting an ECG signal corresponding to the patient'"'"'s ECG waveform corresponding to the periodic electrical heart activity of the patient; selecting a first time-measure of the absorption signal including a maximum and minimum amplitude change in absorption; selecting a second time-measure of the ECG signal including components corresponding to the occurrence of the heartbeat; correlating the ECG signal and the absorption signal by multiplying the first time-measure of the absorption signal and the second time-measure of the ECG signal together to form a waveform product and thereafter shifting the time-measure of the absorption signal backwards in time relative to the time-measure of the ECG signal and multiplying the shifted and unshifted waveforms together to identify a maximum waveform product corresponding to the product of the ECG signal corresponding to the occurrence of the heartbeat and the maximum amplitude of the absorption signal; processing the absorption signal and the determined correlation to identify the periodic changes in the absorption signal associated with the determined maximum waveform product likely to correspond to arterial pulses in the patient'"'"'s blood flow characteristics; and calculating the amount of the blood constituent from the identified periodic changes in the absorption signal. - View Dependent Claims (2, 3, 4)
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5. Apparatus for calculating .[.the.]. .Iadd.an .Iaddend.amount of a blood constituent from the blood flow characteristics of a patient comprising:
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means for photoelectrically detecting an absorption signal corresponding to .[.the.]. absorption of light measured at two or more wavelengths in the patient'"'"'s tissue including periodic changes caused by periodic arterial pulses in the blood flow characteristics and aperiodic changes unrelated to the patient'"'"'s heartbeat; means for electrically detecting an ECG signal corresponding to the patient'"'"'s ECG waveform corresponding to the periodic electrical heart activity of the patient; means for selecting a first time-measure of the absorption signal including a maximum and minimum amplitude change in absorption; means for selecting a second time-measuring of the ECG signal including components corresponding to the occurrence of the heartbeat; means for correlating the ECG signal and the absorption signal by multiplying the first time-measure of the absorption and the second time-measure of the ECG signal together to form a waveform product and thereafter shifting the time-measure of the absorption signal backwards in time relative to the time-measure of the ECG signal and multiplying the shifted and unshifted waveforms together to identify a maximum waveform product corresponding to the product of the ECG signal corresponding to the occurrence of the heartbeat and the maximum amplitude of the absorption signal; means for processing the absorption signal and the determined correlation to identify the periodic changes in the absorption signal associated with the determined maximum waveform product likely to correspond to arterial pulses in the patient'"'"'s blood flow characteristics; and means for calculating the amount of the blood constituent from the identified periodic changes in the absorption signal. - View Dependent Claims (6, 7, 8)
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9. A method for calculating .[.the.]. .Iadd.an .Iaddend.amount of a blood constituent from a patient'"'"'s blood flow characteristics including aperiodic information corresponding to artifacts and periodic information corresponding to arterial pulses, comprising:
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.Iadd.directing light of two or more wavelengths toward the patient'"'"'s tissue;
.Iaddend.detecting a set of first signals representing .[.the.]. absorption of light measured at .Iadd.said .Iaddend.two or more wavelengths .[.of light.]. in the patient'"'"'s tissue including detected information corresponding to changes in absorption as a result of changes in the blood flow characteristics; detecting a second signal representing the occurrences of a selected portion of .[.the.]. .Iadd.an .Iaddend.ECG waveform of the patient; processing the first and second signals to enhance .[.the.]. periodic information contained in each individual signal whereby the first signals are processed in a repetitive manner, one discrete portion at a time, and the occurrence of a selected portion of the patient'"'"'s ECG waveform in the second signal initiates processing of a discrete portion of the first signals; and calculating the amount of .Iadd.said .Iaddend.blood constituent using the enhanced periodic information in the processed portions of the first signals. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. Apparatus for calculating .[.the.]. .Iadd.an .Iaddend.amount of a blood constituent from a patient'"'"'s blood flow characteristics including arterial pulses and artifacts comprising:
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means for photoelectrically detecting a set of first signals representing the absorption of light measured at two or more wavelengths in the patient'"'"'s tissue including detected information corresponding to changes in absorption as a result of changes in the blood flow characteristics; means for detecting a second signal representing the occurrences of a selected portion of .[.the patient'"'"'s.]. .Iadd.an .Iaddend.ECG waveform .Iadd.of the patient.Iaddend.; means for processing the first and second signals to enhance the periodic information contained in each individual signal whereby each occurrence of .[.a.]. .Iadd.said .Iaddend.selected portion in the second signal initiates processing of .[.a.]. discrete portions of the first signals so that the information in the first signals are processed in a repetitive manner; and means for calculating the amount of .Iadd.said .Iaddend.blood constituent using the enhanced information in the processed portions of the first signals. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. A method of calculating an amount of a blood constituent from the blood flow characteristics of a patient comprising:
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subjecting the patient'"'"'s tissue to electromagnetic energy, thereby facilitating the transformation of arterial blood flow in the patient'"'"'s tissue into a blood flow signal, the blood flow signal corresponding to the arterial blood flow including periodic changes caused by periodic arterial pulses in the blood flow characteristics and changes caused by artifact; detecting the blood flow signal; detecting the occurrence of a heartbeat of the patient; correlating the detected blood flow signal and the occurrence of a heartbeat; processing the blood flow signal and the determined correlation to identify the periodic changes in the blood flow signal likely to correspond to arterial pulses in the patient'"'"'s blood flow characteristics; and calculating the amount of the blood constituent from the identified periodic changes in the blood flow signal. .Iaddend. .Iadd. - View Dependent Claims (31, 32, 33, 34)
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Specification