Patent ID: 8271085

Claim:
An implantable medical device including: a. an impedance or admittance determination unit which is connected or is to be connected to electrodes to be placed intracardially or intraluminally for delivering a measuring current; b. an alternating current or AC voltage source which (1) generates (a) a measuring current as an alternating current of constant current amplitude, or (b) a measuring voltage as an AC voltage of constant voltage amplitude, and (2) feeds the measuring current or measuring voltage into the electrodes at different frequencies, the frequencies being below 500 kHz; c. a measuring unit which detects: (1) a voltage drop between two of the electrodes as a result of the fed measuring current, or (2) the current strength between two of the electrodes as a result of the fed measuring voltage; d. an analysis unit connected to the alternating current or AC voltage source and the measuring unit, wherein the analysis unit calculates: (1) pairs of impedance values or admittance values from: (a) the fed measuring current and the voltage drop detected as a result thereof, or (b) the fed measuring voltage and the current strength detected as a result thereof, each pair arising from different frequencies of the measuring current or measuring voltage; (2) a value for a blood impedance component or a blood admittance component which is at least substantially independent of the impedance or admittance of the body tissue surrounding a blood vessel from which the pairs of impedance values or admittance values are collected; (3) a relative change of the value of the blood impedance component or blood admittance component over time, the relative change serving as a measure of a change in blood hematocrit value.