The present invention relates in general to electrocardiographic (ECG) and oxygen saturation signal recording and more particularly concerns a novel technique for processing the ECG and oxygen saturation signals.
For background on ECG and oxygen saturation signal recording reference is made to U.S. Pat. No. 6,125,296.
A typical prior art approach for measuring oxygen saturation uses either a large nonportable bedside unit or a portable unit with recording capability.
An object of this invention is to provide an automatic mechanism for identifying those portions of the recorded pulse oxymetry data signals that are invalid.
Another object of the invention is to use pulse oxymetry data signals, which this invention determines as valid, and identify those segments of the data signals that are valid desaturation signals.
In one aspect, the invention is a method for processing pulse oxymetry data signals. The method includes recording pulse oxymetry data signals. The pulse oxymetry data signals have a plurality of oxymetry waveforms. The pulse oxymetry data signals correspond to oxygen saturation data signals. The method also includes determining a correlation coefficient between sequential oxymetry waveforms and identifying a valid pulse oxymetry waveform.
This aspect of the invention may have one or more of the following features. Determining the correlation coefficient includes storing a first pulse oxymetry waveform segment having a first length in a first buffer, copying the first pulse oxymetry waveform segment from the first buffer to a second buffer, copying a second pulse oxymetry waveform segment having a second length to the first buffer, comparing the first length, the second length and a predetermined value, and determining a correlation length related to the first and second lengths and the predetermined value. Determining a correlation length includes taking the minimum of the first length, the second length, and the predetermined value. Determining a correlation coefficient includes determining a correlation coefficient from the first pulse oxymetry waveform segment and the second pulse oxymetry waveform segment, comparing the correlation coefficient to a threshold value, and filtering out an invalid pulse oxymetry waveform segment that has a correlation coefficient below the threshold value. Filtering out the invalid pulse oxymetry waveform segment includes eliminating pulse oxymetry waveform segments if 75% of the correlation coefficients for the last 6 seconds are above the threshold value of 0.9. The method also includes determining valid oxygen desaturation data signals. Determining valid desaturation signals comprises labeling oxygen saturation signals below a threshold value for a predetermined time as valid desaturation data. The threshold value is 88% and the predetermined time is 300 seconds. Determining valid desaturation signals comprises eliminating artifacts. Determining valid desaturation signals comprises ignoring desaturation signals below the threshold value that do not reach a peak value.
In another aspect, the invention is an apparatus for processing pulse oxymetry data signals. The apparatus includes a memory that stores executable instruction data signals and a processor. The processor executes the instruction data signals to record the pulse oxymetry data. The pulse oxymetry data has a plurality of oxymetry waveforms. The pulse oxymetry data signals correspond to oxygen saturation data signals. The processor also executes the instruction data signals to determine a correlation coefficient between sequential oxymetry waveforms and to identify invalid pulse oxymetry waveforms.
This aspect of the invention may have one or more of the following features. Determining the correlation coefficient includes storing a first pulse oxymetry waveform segment having a first length in a first buffer, copying the first pulse oxymetry waveform segment from the first buffer to a second buffer, copying a second pulse oxymetry waveform segment having a second length to the first buffer, comparing the first length, the second length and a predetermined value, and determining a correlation length related to the first and second lengths and the predetermined value. Determining a correlation length includes taking the minimum of the first length, the second length, and the predetermined value. Determining a correlation coefficient includes determining a correlation coefficient from the first pulse oxymetry waveform segment and the second pulse oxymetry waveform segment, comparing the correlation coefficient to a threshold value, and filtering out an invalid pulse oxymetry waveform segment that has a correlation coefficient below the threshold value. Filtering out the invalid pulse oxymetry waveform segment includes eliminating pulse oxymetry waveform segments if 75% of the correlation coefficients for the last 6 seconds are above the threshold value of 0.9. The processor also executes the instruction data signals to determine valid oxygen desaturation data signals. Determining valid desaturation signals comprises labeling oxygen saturation signals below a threshold value for a predetermined time as valid desaturation data. The threshold value is 88% and the predetermined time is 300 seconds. Determining valid desaturation signals comprises eliminating artifacts. Determining valid desaturation signals comprises ignoring desaturation signals below the threshold value that do not reach a peak value.
In still another aspect, the invention is an article that includes a machine-readable medium that stores executable instruction signals for processing pulse oxymetry data signals. The instruction signals cause a machine to record the pulse oxymetry data signals. The pulse oxymetry data signals have a plurality of oxymetry waveforms. The pulse oxymetry data signals correspond to oxygen saturation data signals. The instructions also cause a machine to determine a correlation coefficient between sequential oxymetry waveforms and to identify invalid pulse oxymetry waveforms.
This aspect of the invention may have one or more of the following features. Determining the correlation coefficient includes storing a first pulse oxymetry waveform segment having a first length in a first buffer, copying the first pulse oxymetry waveform segment from the first buffer to a second buffer, copying a second pulse oxymetry waveform segment having a second length to the first buffer, comparing the first length, the second length and a predetermined value, and determining a correlation length related to the first and second lengths and the predetermined value. Determining a correlation length includes taking the minimum of the first length, the second length, and the predetermined value. Determining a correlation coefficient includes determining a correlation coefficient from the first pulse oxymetry waveform segment and the second pulse oxymetry waveform segment, comparing the correlation coefficient to a threshold value, and filtering out an invalid pulse oxymetry waveform segment that has a correlation coefficient below the threshold value. Filtering out the invalid pulse oxymetry waveform segment includes eliminating pulse oxymetry waveform segments if 75% of the correlation coefficients for the last 6 seconds are above the threshold value of 0.9. The instructions also cause a machine to determine valid oxygen desaturation data signals. Determining valid desaturation signals comprises labeling oxygen saturation signals below a threshold value for a predetermined time as valid desaturation data. The threshold value is 88% and the predetermined time is 300 seconds. Determining valid desaturation signals comprises eliminating artifacts. Determining valid desaturation signals comprises ignoring desaturation signals below the threshold value that do not reach a peak value.
Some or all of the aspects of the invention described above may have some or all of the following advantages. The invention makes it impossible to automatically differentiate valid oxymetry data signals from invalid oxymetry data signals. The invention also automatically determines true desaturation signals from invalid desaturation signals.
Other features, objects and advantages will become apparent from the following detailed description when read in connection with the accompanying drawing in which: