Broadband spectroscopy of dynamic impedances with short chirp pulses.

An impedance spectrum of dynamic systems is time dependent. Fast impedance changes take place, for example, in high throughput microfluidic devices and in operating cardiovascular systems. Measurements must be as short as possible to avoid significant impedance changes during the spectrum analysis, and as long as possible for enlarging the excitation energy and obtaining a better signal-to-noise ratio (SNR). The authors propose to use specific short chirp pulses for excitation. Thanks to the specific properties of the chirp function, it is possible to meet the needs for a spectrum bandwidth, measurement time and SNR so that the most accurate impedance spectrogram can be obtained. The chirp wave excitation can include thousands of cycles when the impedance changes slowly, but in the case of very high speed changes it can be shorter than a single cycle, preserving the same excitation bandwidth. For example, a 100 kHz bandwidth can be covered by the chirp pulse with durations from 10 µs to 1 s; only its excitation energy differs also 10(5) times. After discussing theoretical short chirp properties in detail, the authors show how to generate short chirps in the microsecond range with a bandwidth up to a few MHz by using digital synthesis architectures developed inside a low-cost standard field programmable gate array.

A sampling multichannel bioimpedance analyzer for tissue monitoring.

The paper focuses on principles of designing of a multichannel bioimpedance analyzer based on simultaneous multisine measurement. The measurement task arises due to the need to monitor patients during and after heart surgery operation performing MIMO (multiple-input-multiple-output) bioimpedance measurement. Frequencies of the simultaneously applied sinusoidal excitations must be close but simultaneously varied in a larger range (e.g. from 1 kHz up to 10 MHz). The main idea of the proposed approach is that the use of a rather specific signal system (frequencies of sinusoidal excitations are related as integers and sampling frequencies are properly related/adapted to them) makes it possible to separate responses to different excitations from the measured summary signals by means of a quite simple filter and different (under) sampling rates.

Modification of pulse wave signals in electrical bioimpedance analyzers for implantable medical devices.

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.

Thoracic bioimpedance as a basis for pacing control.

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.