Patent ID: 8880155

Claim:
A method, comprising: using a processor: receiving a plethysmographic waveform signal from a sensor applied to a patient; determining one or more features of the plethysmographic waveform over time; correlating in time the one or more features of the plethysmographic waveform to at least one of an exhalation portion or an inhalation portion of a respiratory cycle of the patient; and determining a measure of the patient's blood volume based on a change in the one or more features of the plethysmographic waveform correlated in time with the respiratory cycle during the at least one of the exhalation portion or the inhalation portion of the respiratory cycle, wherein the one or more features comprise a pulse amplitude and wherein an increase in pulse amplitude during the exhalation portion of the respiratory cycle that is greater than a range or threshold is indicative of a change in the patient's blood volume.