Physiological monitoring methods and systems utilizing filter scaling

A method for determining a physiological parameter of a subject using a pulse oximeter, the method comprising:

• generating, using a pulse oximetry sensor, a photoplethysmography (PPG) signal, wherein the pulse oximetry sensor is configured to detect light attenuated by the subject;
• setting a light detection gain level, using a gain controller;
• filtering the PPG signal, using a filter, wherein the filter comprises at least one of filter history and filter coefficients;
• determining, using a processor of the pulse oximeter, at least one of a power level and the light detection gain level;
• calculating, using the processor of the pulse oximeter, a scaling factor based on at least one of the determined power level and the determined light detection gain level, wherein calculating the scaling factor comprises calculating the scaling factor by multiplying the determined power level and the determined light detection gain level;
• scaling, using the processor of the pulse oximeter, the at least one of a filter history and filter coefficients using the scaling factor, wherein scaling comprises scaling the filter history by a ratio of the calculated scaling factor and a previous scaling factor;
• determining, using the processor of the pulse oximeter, the physiological parameter based on the PPG signal that was filtered by the filter;
• and
• displaying, using a display of the pulse oximeter, the physiological parameter of the subject.