Multichannel tetrapolar admittance meter (MY) for intracardiac volume measurements in animals.

With an 8-electrode catheter, this instrument measures simultaneously five intraventricular sections of admittance and, also, total admittance, the latter obtained as the sum of five component sections. It injects through the two outermost electrodes of the catheter a constant current (828 microA rms) of high frequency (14 kHz). Actually, the instrument measures the mathematical inverse of the resistive component (conductance) of the impedance seen by the voltage sensing electrodes. The sensitivity per channel was adjusted to 25 V/mho, resulting in an overall sensitivity of 5.28 V/mho for the total intraventricular admittance. Nonlinearity in any single channel was less than or equal to 3.4% while, for the total admittance, it was less than or equal to 1.5%. The difference between any two individual channels when the same calibration resistor was connected, relative to the expected value, was less than or equal to 4.8%. The equipment demonstrated good performance in animal experiments and showed the possibility of detecting localized dysfunctions. Human applications still remain to be done.