"The method involves obtaining a pleth signal that is modulated based on interaction of a transmitted optical signal with a patient's blood (e.g., arterial blood and/or perfused tissue), processing the pleth signal to identify an effect related to the Mayer Wave, and providing an output related to the Mayer Wave effect (e.g., a waveform, one or more values or other information, e.g., related to the" . . . .