Changes in local blood flow of the brain stem in acute intracranial hypertension. Experimental study

Abstract

The effect of supratentorial mass lesions on the local cerebral blood flow (1CBF) of the brain-stem was evaluated with special reference to the following three points. 1) The level of the intracranial pressure (ICP) at which the 1CBF of the brain-stem begins to decrease. 2) Alterations in the 1CBF of the upper brain-stem at the beginning of uncal herniation. 3) Alterations in the 1CBF of the medulla oblongata during the Cushing response. Using 40 cats, platinum electrodes were placed stereotaxically in the thalamus (Th), inferior colliculus (IC), and medulla oblongata (MO) for measurement of 1CBF by the hydrogen clearance method. The 1CBF of the brain-stem was serially measured before and after intermittent increase in ICP produced by inflation of an extradural balloon. Arterial blood pressure and supra and infratentorial extradural pressures were continuously recorded. The mean control 1CBF in the Th, IC, and MO were 37.5±9.9, 42.1±8.6, and 30.7±4.9 ml/100 g/min, respectively. At 20 to 30mmHg of supratentorial pressure (STP), the 1CBF of the Th started to decrease, and at 20 to 30mmHg of infratentorial pressure (ITP), the 1CBF of the IC started to decrease. Finally, at 40 to 60mmHg of ITP, the 1CBF of the MO was affected. At the beginning of the uncal herniation suggested by anisocoria, the mean 1CBF of the IC abruptly decreased from 33.7 to 19.6 ml/100 g/min (n = 16). In this stage, the pressure gradient between the supra and infratentorial spaces was 24.6±11.4mmHg. The Cushing response was evoked at STP 93.4±14.6mmHg and ITP of 49.9±6.8mmHg (n=16). The blood pressure significantly increased from 121.5 to 140.OmmHg. However, immediately before and during vasopressor response, little change was noted in the mean cerebral perfusion pressure (CPP) of the posterior fossa, i.e., from 89.0 to 89.6mmHg. The 1CBF of the MO did not show significant change either, i.e., from 22.8 to 20.9 ml/100 g/min. The data suggested that in supratentorial mass lesion, the 1CBF of the thalamus decreased first, followed by the 1CBF of the inferior colliculus, and then of the medulla oblongata. At the beginning of uncal herniation, the 1CBF of the upper brain-stem markedly decreased. During the Cushing response, the 1CBF of the MO did not change significantly.