RESUMO
The problems of application of pulse wave signals in electrical bioimpedance analyzers foreseen for using in implantable medical devices as diagnostical means are discussed in this paper. The main problem arises at measurement of phasor parameters by the aid of rectangular pulse wave signals. The specific measurement errors appear due to presence of higher harmonics in the spectra of pulse waveforms. These errors are discussed in two cases, in the case of full cycle rectangular waveform, and in the case of using the shortened pulses introduced specially for reduction of errors.
RESUMO
Periodic variations of the thoracic bioimpedance due to breathing and heartbeating carry confidential information that is used for pacing rate control in rate-adaptive pacemakers. The respiratory parameters--the respiration rate and tidal volume--are detected from the filtered breathing signal component (0.1 to 1.0 Hz), and are used for fuzzy feed-forward adaptive control of the pacing rate to meet the needs of the organism. The cardiac parameters--the actual heart rate and stroke volume--are measured from the heartbeating signal component (1.0 to 3.0 Hz) and are proposed for feedback correction of the feed-forward control to meet the heart's ability. The problems of electrical bioimpedance measurement and design of the rate-adaptive pacemaker, wherein the intracardiac impedance is used as the main information source for pacing control, are discussed in this paper.
