Patent ID: 7092757

Claim:
A minute ventilation sensing device, comprising: excitation current electrodes for imposing a current field in the thoracic cavity; an exciter for supplying excitation current between the excitation current electrodes as a bipolar excitation current waveform at a specified excitation frequency and amplitude, wherein the excitation current waveform is output as a strobe made up of a specified number of excitation current waveform cycles with each strobe repeated at a specified strobing frequency; voltage sense electrodes for generating a voltage sense signal corresponding to a potential difference between two points in the thoracic cavity; sampling circuitry for sampling the voltage sense signal during the excitation waveform strobe at a specified sampling rate that corresponds to the excitation frequency; circuitry for initiating a noise detection operation wherein the voltage sense signal is sampled when no excitation current is supplied and the samples are then processed to detect a noise level; and, circuitry means for adjusting the excitation current in accordance with the detected noise level, wherein the excitation current adjusting circuitry means adjusts the excitation current amplitude in response to a detected noise level in order to approximately maintain a specified signal-to-noise ratio.