Patent ID: 8414499

Claim:
A plethysmograph variability method comprising: inputting a plethysmograph waveform having pulses corresponding to pulsatile blood flow within a tissue site; deriving a plurality of perfusion values corresponding to the pulses, wherein deriving the plurality of perfusion values comprises: identifying of the pulses and valleys of the pulses, calculating differential values for the pulses from the peaks of the pulses and the valleys of the pulses, determining reference values for the pulses, and normalizing the differential values with the reference values; determining a plurality of variability values indicative of the variability of a plurality of series of perfusion values, wherein each variability value is determined by calculating a difference between a first perfusion value of a series of perfusion values and a second perfusion value of the series of perfusion values and normalizing the difference with the first perfusion value; calculating a plethysmograph variability parameter representative of the plurality of variability values; and displaying the plethysmograph variability parameter.