[Postmortem behavior of impulse transmission latency--impulse transmission strength curves]

Strength-duration curves (i/t-curve) are describing the dependence of the threshold intensity of rectangular impulses from their duration; in clinical neurophysiology they help to clarify whether a muscle is denervated or not. In the post-mortem interval from 2 to 9 hpm the pm. changes of strength-duration-curves were investigated on 17 bodies; muscular contraction was objectified using a sensitive force transducer pricked into the muscle. The muscle was stimulated with constant-current rectangular impulses of 5 to 1000 msec. duration and current intensities which produce a force of muscular contraction of 2.5 mN each half an hour. The strength-duration-curves of human bodies taken at the earliest possible time p. m. (2 hpm) show already the pattern of partially or total denervation (steep rise of threshold values for duration of stimuli shorter than 100 msec). As for the rheobase there is a strong linear relationship between ln of the threshold and time since death for duration of stimuli below 1000 msec. Extrapolation of the time since death on the basis of threshold values of different duration of stimulations of an i/t-curve reveals only small rise of precision of death time estimation compared to extrapolation of the time since death just with the rheobase.