Methods and systems for determining a respiration rate (RR) of asubject are disclosed. In one embodiment, a method includes sampling a PPGsignal at a first frequency, filtering the PPG signal with a first high-passfilter, receiving an output from the first high-pass filter and filtering theoutput at a second frequency in a second high-pass filter, counting positive-andnegative-edge pulses of a portion of the PPG signal to determine breath-timeintervals caused by an influence of the respiration rate on the PPGsignal, and determining an average of the breath-time intervals for thepositive-edge zero-crossings and the negative-edge zero-crossings to derive anestimate of the RR. In other embodiments, a central frequency of componentsof the PPG signal is determined based on bandpass filters and a feedbackmechanism to estimate 3 and select an appropriate adaptive filter todetermine the RR. Other methods and systems are disclosed.
