[Hemodynamic adaptations in proximal cerebrovascular occlusion]

Abstract

In order to gain more insight into the pathophysiology of extracerebral cerebrovascular occlusion, the cerebral hemodynamic behaviour after uni- or bilateral carotid occlusion was investigated. In Wistar rats, acute occlusion of one common carotid artery leads to a moderate bilateral lowering of the resting hemispheric brain blood flow; no interhemispheric perfusion asymmetry is observed. During hypercapnia, however, a manyfold increase of the hemispheric blood flow is seen at the intact side, whereas blood flow increase at the side of the occlusion is suppressed indicating that the cerebrovascular reserve at the side of the occlusion is largely used to preserve resting hemispheric perfusion. During the days (1, 5, 15 and 30) following the occlusion, resting hemispheric blood flow is progressively restored rather rapidly (bilateral normalization on the fifth day) whereas restoration of the cerebrovascular reserve (hemispheric blood flow increase in hypercapnia) proceeds more slowly and a nearly normal hypercapnic response is reached on day thirty. Spontaneously Hypertensive Rats (SHR) show structural abnormalities of their blood vessels during the development of hypertension, leading to impaired adaptation possibilities of the cerebral vasculature after unilateral common carotid occlusion. This is indicated by the striking comparability of the compensation of hemispheric cerebral blood flow (in normo- and hypercapnia) of SH rats five days after unilateral carotid occlusion with the cerebral hemodynamic status of normotensive animals already seen 24 hours after the same occlusion. Consecutive bilateral common carotid occlusion shows that survival rate increases by increasing the interval between both occlusions. This survival relation is much more unfavorable in SH rats. The parallelism between the restoration of the measured CO2-reactivity of the blood flow in the involved hemisphere after unilateral carotid occlusion and the evolution of survival rate after consecutive bilateral carotid occlusion indicates that the response of the hemispheric circulation to CO2 offers a good estimate of true cerebrovascular reserve after cerebrovascular accidents of this kind. In cats, acute bilateral occlusion of the carotid arteries leads to a moderate decrease of resting cerebral blood flow in the anterior parts of the brain (cerebrum); the hypercapnic response of this region is, however, completely abolished. In the posterior brain regions (medulla oblongata and cerebellum) resting blood flow and its increase under hypercapnia are preserved. The experiments indicate that the relative preservation of resting cerebral blood flow in the cerebrum of the cat after acute bilateral carotid occlusion is at the expense of its complete hemodynamic reserve. Posterior brain regions are better protected in these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)