Abstract
The effects of an expanding supratentorial mass on the neural function and local cerebral blood flow (1-CBF) in the brain stem were investigated. A balloon was into the supratentorial epidural space of 32 cats and inflated at a constant rate (0.0197 ml/minute). The auditory brain-stem response (BER) and the short-latency somatosensory evoked response (S-SER) were employed to evaluate the electrical conduction through the auditory and lemniscal pathway, respectively. The blink reflex was also monitored to investigate the neural function of the brain-stem reticular formation. The 1-CBF was measured in the inferior colliculus (IC), medial lemniscus (ML), pontine reticular formation (PRF) and reticular formation of the medulla oblongata (MORF) by the hydrogen clearance method. While the ICP was raised to 40-60 mmHg, the values of IC- and PRF-CBF markedly decreased as compared with those of ML- and MORF-CBF. Blink reflex R2 disappeared at 40-70 mmHg ICP, prior to the disappearance of BER wave V, S-SER II components, and blink reflex R1. At the stage of appearance of anisocoria, the BER wave V disappeared in all cats while the S-SER components were preserved in 4 of 18 cats. When both BER wave V and S-SER II components disappeared, 1-CBFs in IC and ML decreased to less than 50% of the control. The balloon was deflated within 15 minutes after anisocoria occurred. One hour after the deflation, blink reflex R2 remained absent in all cases. S-SER II components and BER wave V recovered in 10 of 14 cats and 4 of 18 cats, respectively. The 1-CBF of the brain-stem improved in the majority of the cats in which the neural function of the corresponding region recovered. These results suggest that the circulation and the neural function of PRF and IC are more vulnerable to intracranial hypertension than those of ML, and an hardly restored by decompression after the evidence of tentorial herniation.
