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

Publisher Website
Google Scholar
Abstract
Summary 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. When a large intracranial cerebral artery such as the middle cerebral artery (MCA) is occluded, the microvasculature in the ischaemic brain area may become maximally dilated, and may exhibit loss of autoregulation and loss of CO2 responsiveness (Harper1, Meyer2, Symon3). Under these conditions the regional cerebral blood flow (rCBF) in the ischaemic area follows passively changes in regional perfusion pressure (rPP). In experimental animals with occlusion of the MCA we studied the ischaemic brain area rPP which depends on: a) the pressure in the occluded MCA, and b) the regional tissue pressure (rTP) in the ischaemic brain area. To measure the pressure in the occluded MCA we introduced a catheter into the MCA at its origin via the transorbital approach. To measure the rTP in the ischaemic area we introduced a so called wick catheter into the brain area supplied by the occluded MCA. The effects of arterial CO2 changes and drug induced hypertension on the rPP were studied in 7 baboons and 5 macaques.