[Effects of intrathoracic pressure on cerebral circulation in the monkey as a function of body posture, sitting or standing].

Sixty-four measurements of CBF were performed in 8 monkeys in supine and in sitting position under various conditions of ventilation. The position of the body does not normally influence the response of brain circulation to CO2. The response is not different from normal with high insufflation pressure in supine position and the capacities to autoregulation seem to be maintained. In vertical position however there are no longer any significant relations between CBF and PaCO2, and the loss of autoregulation seems to occur earlier and to be more marked. Correlation of these findings to neuroradiologic data indicates that the cerebral venous drainage through the meningospinal plexus is enhanced in vertical position and that during intrathoracic hyperpressure the cerebral venous blood is retained in the jugular vein and meningospinal plexus, thus decreasing the cerebral venous pressure increase and maintaining a perfusion of brain tissue compatible with the survival of the animal.