| 摘要 |
A method and apparatus for monitoring changes in the intra-thoracic pressure of a patient due to the patient's respiratory activity or volumetric changes in the extra-thoracic arterial circulatory system due to cardiac function based on the changes in pressure in the patient's extra-thoracic arterial circulatory system as measured by a plethysmography sensor, such as an photoplethysmograph. A frequency spectrum is generated for the plethysmograph signal and the frequencies of interest is isolated from the frequency spectrum by setting appropriate cutoff frequencies for the frequency spectrum. This isolated frequency is used to filter the plethysmograph signal to provide a signal indicative of the patient's respiratory activity or cardiac function. For corrections for breathing frequency roll-off and deviations of the I:E ratio from 1:1.
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