Changes in the resistive and reactive components of abdominal impedance during the 1-21 day post-mortem periods in rats.

The magnitudes of the resistive (R) and reactive (X) components of total abdominal impedance (Zt) at 10 kHz, and of transcellular impedance (Zi), cytoplasmic impedance (Ri) and cell membrane capacitance (C), were calculated from sequential measurements of Zt, phase angle (theta) and extracellular impedance (Ze), in each of eight rat cadavers maintained at 9.0 +/- 1.5 degrees C. Total impedance, theta, R, X, Ze and Ri increased during the first 3 days of death, while C decreased. Thereafter, each of these parameters decreased with increasing post-mortem interval. The data indicate that Zt was predominantly resistive, and that Zt became progressively more resistive, and less reactive, with increasing time since death. Transcellular impedance remained relatively constant during the first 9 days, prior to increasing to more than 160% of its initial (3 h) value at 21 days post-mortem. This change coincided temporally with, and was attributable to, a time-dependent decrease in cell membrane capacitance post-mortem. Further studies, using human post-mortem tissues or body segments, will determine whether or not time-related changes in one or more of the impedance parameters may be used to estimate post-mortem interval.