A method for estimating a blood volume of a mammalian subject uses an electronic apparatus to i) compute a blood volume index from hemodynamic data for the subject, and ii) use the blood volume index to generate an output indicative of an estimated blood volume of the subject. The blood volume index is defined in terms of a baseline electrical body impedance of the subject, a baseline heart rate of the subject, an electrical body impedance of the subject at a time of interest, and a heart rate of the subject at the time of interest. The blood volume index may be further defined in terms of a relative heart rate and a relative electrical body impedance.
