Intracerebral gas partial pressure changes under vasoactive drugs. A mass spectrometry study.

An original technique based on mass spectrometry has been used to measure simultaneously in undrugged, freely-breathing animals local PO2 and PCO2 in the brain (caudate nucleus) and arterial PO2 and PCO2 in the aorta. Injection of vasoactive drugs brought about significant modifications of the partial pressures of the physiological gases in the brain. The origin of these variations was discussed, based on the combination of 3 possible factors: cerebral vascular changes, systemic metabolic changes (PaO2 and PaCO2) and local metabolic changes. It was demonstrated that local variations of PCO2 cannot be held to be responsible for the modifications of cerebral blood flow induced by papaverine or the sympathomimetic drugs.