Non-invasively measuring a physiological parameter by applying to a subject's body part a venous occlusion plethysmographic device including a first section having a first fluid chamber and at least a second region having a second fluid chamber to engage a first region of the body part and a second region of the body part, proximal of the first region； pressurizing the first chamber to a pressure sufficient to compensate for hydrostatic pressure added to the inherent venous pressure at the maximal vertical lowering level of the body part relative to the subject's heart level； intermittently raising and lowering the pressure in the second fluid chamber to a pressure above or equal to the pressure in the first chamber, but below the arterial blood pressure； measuring changes in volume of the first region of the body part； and utilizing the measured volume changes to provide a measure of the physiological parameter.
