Influence of blood pressure on tolerance to an intracranial expanding mass.

In 3 groups of 4 dogs with normotensive, induced-hypotensive and induced-hypertensive blood pressure respectively, continuous expansion of an extradural supratentorial balloon led to respiratory arrest at inflation volumes which increased with increasing blood pressure. This positive correlation between the volume tolerance to an expanding lesion and blood pressure was also found in similar experiments on 4 hypotensive and 4 hypertensive cats. Monitoring cerebrospinal fluid pressures in the cerebral lateral ventricles, in the posterior fossa and in the spinal subarachnoid space showed that absolute pressures in the various compartments as well as the intercompartmental pressure gradients at the moment of respiratory arrest were increased in proportion to the level of the systemic arterial pressure in each case. These observations do not support current concepts that brain-stem distortion alone or that stimulation of baroreceptors in the posterior fossa are responsible for eliciting the Cushing response. The fact that the supratentorial perfusion pressure was the only parameter which did not differ significantly under the different experimental conditions suggests that the mechanism responsible for the respiratory arrest is local brain tissue ischemia, probably near the tentorial incisure. The magnitude of gain in volume tolerance, when mean arterial pressure was varied from 60 mmHg to 190 mmHg, was 87% suggesting that the blood pressure may have a critical role in an intracranial lesion. These findings have clinical implications.