Estimating time of death from measurement of the electrical excitability of skeletal muscle

Post-mortem contraction was measured using sensitive force transducers inserted into human muscle. The muscle was stimulated using rectangular impulses of 1 sec duration and known current intensity. After some time, a noticeable change of the muscular contraction occurred, from a two-peak to a one-peak shape. The maximum force of the muscular contraction using a stable current intensity decreased with time since death, but relaxation time increased. The decrease of the maximum force and the increase of the relaxation time were used as criteria for extrapolating the time since death in a random sample of 50 bodies. The calculated 95% limits of confidence were 2.85 h (decrease of the maximum force) and 2.7 h (increase of relaxation time) up to 13 hours post mortem. The calculated 95% limits of confidence were checked on an independent sample of 21 bodies and proved to be reliable.

[Postmortem behavior of the rheobase]

Own investigations on the postmortem rise of muscular threshold were conducted on 20 bodies with exactly known time of death. Muscular contraction was objectified using a sensitive force transducer. The muscle was excitated using rectangular impulses of 1 second duration of a current intensity which produces a force of muscular contraction of 2.5 mN. These excitations were continued over the postmortem interval until a current intensity of 80 mN doesn't cause a contraction of 2.5 mN any more. Investigations were mainly performed at the thenar muscles. There is a linear relationship between ln of muscular threshold (current intensity) and the time since death (r = 0.965). For any case the linear regression line between ln of muscular threshold and time since death was calculated. With mean values for slope and intercept the time of death was calculated for each measured threshold. Extrapolation of the time since death with mean values also for the slope reveals a much more precise estimation of the time since death than an extrapolation with an individual slope as proposed by Joachim and Feldmann (1980). The method was proved on a random sample of 8 practical cases. The real time since death was always within the 95%-limits of confidence of the extrapolated time since death.

Nonuniformity: a physiologic modulator of contraction and relaxation of the normal heart

Nonuniformity of mechanical performance is inherent to the multicellular nature and specific geometry and configuration of the ventricle of the heart. Although the concept of nonuniformity of the diseased heart is not new, ventricular function and the performance of the heart as a muscular pump cannot be understood unless nonuniform behavior is taken into account, even under normal conditions. Along with the loading conditions throughout the cardiac cycle and the time courses of activation and inactivation, the nonuniform behavior of load and of activation and inactivation in space and in time constitutes a third important determinant of mechanical performance and efficiency of the ventricle during both contraction and relaxation. Hence, a triad (load, activation-inactivation, nonuniformity) of controls regulates systolic function of the normal ventricle. In the diseased heart, even when loading and activation-inactivation are normal, the modulating role played by this nonuniformity can become imbalanced because of abnormal cavity size or shape or because of regional dysfunction. Such an imbalance would diminish external efficiency (the ratio of work performed to oxygen utilized) of the ventricle and result in incoordinate contraction and relaxation. These abnormalities, in turn, could exacerbate manifest cardiac failure.

Local myocardial and global ventricular function compared during positive inotropic medication

The assessment of the pharmacological efficiency of cardiotonic drugs interferes with the complex force generation within the spatially netted myocardial meshwork. By multifocal local force and distance measurements we distinguished "afterloaded" from "unloading" force types, which essentially differ in their transient behaviour during changes in ventricular shape. Histologically we found the "afterloaded" force type in oblique fibre populations whereas the "unloading" force curve is generated in surface parallel fibres. Amrinon reduces pre- and afterload, thus inducing ventricular shrinkage. The resulting rearrangement of the intramural force pattern modifies the transmission of fibre tension to ventricular ejection in a way that contractility indices, derived from left ventricular pressure, become inapplicable. However, direct intracoronary drug injection, monitored by segmental force and distance measurements within the irrigated myocardial area, characterizes Amrinon as a potent positive inotropic drug.