The influence of changes in arterial CO2 and blood pressure on the collateral circulation and the regional perfusion pressure in monkeys with occlusion of the middle cerebral artery.

In 7 baboons and 5 macaques the effects of hypercapnia, hypocapnia, hypertension, and combinations of hypertension plus hypocapnia and of hypertension plus hypercapnia on the regional perfusion pressure (rPP) in the brain area rendered ischaemic by occlusion of the middle cerebral artery (MCA) were studied. A new technique for recording the pressure in the occluded MCA was used. The regional tissue pressure (rTP) was recorded with the so called wick type pressure transducers. Hypercapnia produced a marked decrease in rPP in the ischaemic brain area. Hypertension, especially in combination with hypocapnia, produced a very pronounced increase in rPP in the ischaemic brain area. The clinical implications of these findings are discussed. Occlusion of the homolateral common carotid artery (CCA) was followed by a very slight and transient drop in the occluded MCA pressure. Occlusion of the contralateral CCA was followed by a marked and persistent drop in the occluded MCA pressure.