This is a prospective and observational study designed to determine if the changes observed in finger photoplethysmographic waveform can detect incipient hypovolemia. The investigators will studied 60 blood donor volunteers as a model of slight hypovolemia (8-10% of the volemia). Vital signs and photoplethysmography will be recorded in the thumb of the tested hand during a standard blood donation protocol. Recorded data will be analyzed and compared before and after blood donation .
Hypovolemia caused by acute bleeding increased morbi-mortality in emergency and operatin rooms. Precise real-time diagnosis of incipient acute hypovolemia is lacking at the bedside. We hypothesize that the infrared-red signals of pulse oximetry are sensitive to acute changes in patient's volemia. We aimed to test this hypothesis in a cohort of healthy blood donors as a model of simulated acute hypovolemia.