Experimental head injury in monkeys using rotational acceleration impact (author's transl)

Abstract

Investigations of head injury using monkeys were performed to elucidate the effect of linear as well as rotational acceleration impact to produce brain contusion and concussion. The results of investigations using pure linear acceleration impact, which had already been reported, showed that concussion occurred in all monkeys, but that no visible lesion except subarachnoid hemorrhage was found, even though negative pressure of under minus 1 atmosphere was recorded in the contralateral side of the impact. In this paper, the result of investigation using a newly designed and constructed impactor system to deliver rotational acceleration impact is reported. The impactor system was accelerated by compressed air, 1.5-3.5 kg/cm2 in pressure, and velocity of the impact shaft was 20.2-36.4 m/sec. Under light anesthesia with ketamine hydrochloride, the impact was delivered to the occipital area of 18 monkeys, weighing 5.9 to 10.5 kg, through a restraint mask which was made of iron frame and plaster of Paris for each animal in order to obtain a broad impact area and to avoid fracture. Averaged frontal angular acceleration ranged from 29, 000 to 281, 000 rad/sec2 and its duration was 0.64-4.0 msec. Averaged frontal acceleration was 480-1, 080 G's and its duration was 1.26-4.50 msec. Skull fractures were found in 6 monkeys. Four of them had comminuted and depressed fractures that became fatal within 10 minutes after impact due to laceration of the medulla oblongata and/or of the main intracranial vessels. The remaining two had only multiple linear fractures without depression and these animals recovered from initial concussion. Among the 12 monkeys without any fracture, 11 recovered from the initial concussion within 10 minutes after the impact. One monkey died in the state of concussion. There was noted correlation between the severity of concussion and changes in systemic blood pressure immediately after the impact, which is classified into three groups (Fig. 3). Among the 12 monkeys without fracture, 7 had cortical hemorrhage and contusion at the para-sagittal area, tip or base of the frontal and temporal lobe (viz. contre coup injury), or the brain stem and the upper cervical cord. Coup injury in the occipital lobe did not result in this series with the exception of the comminuted depressed fracture group. Intramedullary hemorrhage in the upper cervical cord was found in 5 monkeys; 2 with and 3 without fracture. Four among these 5 survived apnea followed by irregular respiration for several seconds after the impact. As reported previously, pure linear acceleration impact did not produce any visible brain lesion. On the other hand, rotational acceleration impact caused brain damages. It was, therefore, supposed that rotational acceleration impact was a greater cause for producing blunt brain injury than translational impact. Furthermore, it was suggested that the contusion threshold of the brain was close to the concussion threshold.