Patent ID: 8103326

Claim:
A device, comprising: an exciter for outputting an excitation current waveform and impressing a current field between a pair of excitation current electrodes; voltage sensing circuitry for sensing a voltage difference signal between a pair of voltage sense electrodes disposed in a patient's blood and in the current field; means for measuring an electrolyte concentration in the patient's blood; a controller interfaced to the voltage sensing circuitry which is programmed to estimate the patient's hematocrit from the voltage difference signal and the measured electrolyte concentration; and, wherein the controller is programmed to estimate the patient's hematocrit with a mapping function which maps a capacitance value derived from the voltage difference signal to a hematocrit value and programmed to derive a capacitance value from the voltage difference signal by deriving a resistance value from the voltage difference signal at a first excitation frequency and measuring a phase angle between the excitation current waveform and the voltage difference signal at a second excitation frequency.