A new measuring and identification approach for time-varying bioimpedance using multisine electrical impedance spectroscopy
Faculty of Applied Engineering Sciences

article

2013
Bristol :IOP
, 2013

Engineering sciences. Technology

Physiological measurement / Institute of Physical Sciences in Medicine. - Bristol, 1980, currens

34(2013)
:3
, p. 339-357

0967-3334

000315441100009

E

English (eng)

The bioimpedance measurement/identification of time-varying biological systems Z(omega, t) by means of electrical impedance spectroscopy (EIS) is still a challenge today. This paper presents a novel measurement and identification approach, the so-called parametric-in-time approach, valid for time-varying (bio-) impedance systems with a (quasi) periodic character. The technique is based on multisine EIS. Contrary to the widely used nonparametric-in-time strategy, the (bio-) impedance Z(omega, t) is assumed to be time-variant during the measurement interval. Therefore, time-varying spectral analysis tools are required. This new parametric-in-time measuring/identification technique has experimentally been validated through three independent sets of in situ measurements of in vivo myocardial impedance. We show that the time-varying myocardial impedance Z(omega, t) is dominantly periodically time varying (PTV), denoted as Z(PTV)(omega, t). From the temporal analysis of Z(PTV)(omega, t), we demonstrate that it is possible to decompose Z(PTV)(omega, t) into a(n) (in) finite sum of fundamental (bio-) impedance spectra, the so-called harmonic impedance spectra (HIS) Z(k)(omega)s with k is an element of Z. This is similar to the well-known Fourier series of a periodic signal, but now understood at the level of a periodic system's frequency response. The HIS Z(k)(omega) s for k is an element of Z \{0} actually summarize in the bi-frequency (omega, k) domain all the temporal in-cycle information about the periodic changes of Z(omega, t). For the particular case k = 0 (i.e. on the omega-axis), Z(0)(omega) reflects the mean in-cycle behavior of the time-varying bioimpedance. Finally, the HIS Z(k)(omega)s are directly identified from noisy current and voltage myocardium measurements at the multisine measurement frequencies ( i.e. nonparametric-in-frequency).

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