Thoracic Force-deflection Studies in Primates?-s

Thoracic force-deflection characteristics have been measured in the living subhuman primate as a step towards the analysis of cardio-thoracic injuries. Mechanisms of injury were investigated by subjecting Rhesus monkeys seated on a sled to static and dynamic chest displacements (24 tests) by means of a charge fired projectile equipped with a 3 in. dia. impact plate and compensated strain gauges. Forces up to 30 lb were developed in the static press tests for 2 in. deflections. Dynamic tests were run with similar deflections at 3 different initial impact velocities: 36-45 ftlsec, 43-57 ftlsec and 65-85 ftlsec with corresponding peak forces at 80-245 lb, 150-370 lb and 4 lo-700 lb. The thorax of the Rhesus monkey thus shows a very low linear stiffness under static loading but then exhibits a progressive change with increasing velocity, showing more of a spring-masslike response with an initial linear region of stiffness followed by a pronounced drop off. These data may thus help explain the wide disparity noted between human thoracic behavior during closed chest heart massage and that noted in full scale cadaver tests.