Patent ID: 8343057

Claim:
A non-invasive cardiac monitoring system comprising: a photoemitter adapted to transmit light through a portion of a patient's extra-thoracic arterial circulation; a photodetector adapted to receive light after having been transmitted through such a patient and for outputting a first signal based on the received light; and processing electronics configured to produce a cardiac pressure signal as a measure of such a patient's cardiac function by: identifying a respiratory rate frequency component fRR present in the first signal; identifying a heart rate frequency component fHR present in the first signal; filtering the first signal to isolate cardiac related pressure variations in the first signal from respiratory related pressure variations in the first signal with a filter that is dynamically adjusted based on the identified respiratory rate frequency component fRR and the identified heart rate frequency component fHR so as to isolate the heart rate frequency component fRR from the respiratory rate frequency component fRR to produce the cardiac pressure signal; wherein the filter is dynamically adjusted by (1) setting a cutoff frequency fcutoff as fHR−fsmear responsive to the respiratory rate frequency component fRR being less than the heart rate frequency component fHR, and (2) setting the cutoff frequency fcutoff as fHR+fsmear responsive to the respiratory rate frequency component fRR being greater than the heart rate frequency component fHR, where fsmear is a predetermined threshold frequency.