This study was carried out to evaluate the effect of supratentorial mass lesions on the local cerebral blood flow (1-CBF) of the brain-stem with special reference to the following three points: the level of the intracranial pressure (ICP) at which the 1-CBF of the brain-stem begins to decrease, alterations in the 1-CBF of the upper brain-stem at the beginning of uncal herniation, and alterations in the 1-CBF of the medulla oblongata during the Cushing's vasopressor response. Platinum electrodes were placed stereotaxically in the thalamus (Th), inferior colliculus (IC) and medulla oblongata (MO) of 40 cats for measurement of 1-CBF by the hydrogen clearance method. The 1-CBF of the brain-stem was serially measured before and after intermittent increases in ICP produced by the inflation of an extradural balloon. Arterial blood pressure, supra- and infratentorial extradural pressure were continuously recorded. The mean control 1-CBF in the Th, IC and MO were 37.5±9.9, 42.1±8.6 and 30.7±4.9 ml/100g/min, respectively. At 20 to 30 mmHg of supratentorial pressure (STP), the 1-CBF of the Th started to decrease, and at 20 to 30 mmHg of infratentorial pressure (ITP), the 1-CBF of the IC started to decrease. Finally at 40 to 60 mmHg of ITP, the 1-CBF of the MO was affected. At the beginning of uncal herniation, indicated by anisocoria, the mean 1-CBF of the IC abruptly decreased from 33.7 to 19.6 ml/100g/min (n=16). In this stage, the pressure gradient between the supra- and infratentorial spaces was 24.6±11.4 mmHg. The Cushing's vasopressor response was evoked at the STP of 93.4±14.6 mmHg and ITP of 49.9±6.8 mmHg (n=16). The blood pressure significantly increased from 121.5 to 140.0 mmHg, however, immediately before and during vasopressor response, there was only a slight, 0.6 mmHg change in the mean cerebral perfusion pressure (CPP) of the posterior fossa. The 1-CBF of the MO also did not show a significant change. The data suggest that in supratentorial mass lesions, the 1-CBF of the thalamus decreases first, followed by the 1-CBF of the inferior colliculus, and then the medulla oblongata, in that order. At the beginning of uncal herniation, the 1-CBF of the upper brain-stem markedly decreased. During the Cushing's vasopressor response, the 1-CBF of the MO did not change significantly.
Cerebral blood flow of the brain-stem
Hydrogen clearance method