Charles W. Gadd

Measurement of the shortening of cardiac fibers in man

Abstract A newly devised instrument is described which permits measurement of shortening of the fibers through the internal surface of individual cardiac chambers throughout the cardiac cycle in intact, unanesthetized man. It consists of a strain gauge assembly that is an intracardiac catheter through which a flexible stylet is inserted with two extendable prongs to each of which a strain gauge is attached. The two prongs are inserted through the endocardium into the myocardium. The strain gauge assembly is connected to a full-bridged circuit, and the strain in the gauges is optically recorded. It is demonstrated that the strain in the gauges is lineally related to the spacing of the prongs. Thus, the recording represents the changes in distances between fixed points on the internal surface of the ventricles. The instrument has been found to be safe and has been employed in 12 patients without complications. Changes in the shortening of cardiac fibers and cardiac dimensions after administration of nitroglycerin and propranolol are briefly discussed.

Significance of rate of onset in impact injury evaluation

The concept of rate of onset as an injury potential index is critically discussed through the analysis of a wide range of noninjurious whole body decelerations and localized impacts. Examination of the physical data shows that extremely high rates of onset are tolerable without injury and that these levels of rate of onset are reciprocally dependent on the pulse rise time. The physical data is next discussed with reference to existing acceleration injury criteria, specifically the GSI and HIC indices. This work substantiates the conclusions that a single rate of onset tolerance level is not warranted and that rate of onset is not a proven injury potential index.

Nonlinear viscoelastic model for head impact injury hazard

This study explores the application of viscoelastic modeling for characterization of the response of the brain to impulsive loading with the objective of learning whether such models could exhibit the same time dependency of strain or likelihood of injury, as exhibited by the Severity Index, HIC Index, Wayne Tolerance Curve, and other similar representations of tolerance. The mathematical relationships between viscoelastic properties and the corresponding time dependency of tolerance are shown for Newtonian, Bingham plastic, and Pseudo-Bingham, as well as more general behavior. Preliminary static and dynamic tests upon small mammalian material are described with particular attention given to strain in the vicinity of the brainstem as a function of loading profile. Both the theoretical and experimental results show that the falling time dependency of the above indexes can be interpreted in terms of nonlinear viscoelastic response.