Disturbance of cerebral blood flow autoregulation in hypertension is attributable to ischaemia following subarachnoid haemorrhage in rats: A PET study.

Abstract

The effects of subarachnoid haemorrhage (SAH) on cerebral blood flow (CBF) autoregulation during induced hypertension were studied by positron emission tomography (PET) during chronic vasospasm in anaesthetized Sprague-Dawley rats. SAH was induced by intracisternal injection of autologous blood. In the control animals saline was injected instead. This method produced angiographical vasospasm of major arteries 48 h after injection. During this period, CBF was measured at each side of fronto-parietal and occipital sections using PET with or without induced hypertension. Mean arterial blood pressure (MABP) was increased from 94+/-2.4 to 140+/-0.3 mmHg by the injection of phenylephrine. An autoregulatory index (AI) expressed as delta CBF (%) per 10-mmHg increase in MABP was employed to analyse CBF response. SAH significantly reduced (p<0. 0001) basal CBF (ml/100 g/min) by 26.2% (control 60.0+/-1.9 n=24, SAH 44.3+/-4.5 n=20). A territorial CBF that decreased by 50% or more over the mean control value was used to define ischaemia and was identified in five out of 20 regions (25%) in the SAH group. AI (%/10-mmHg) was 13.5+/-2.4 in the control group (n=24). In the SAH group, AI decreased (p<0.05) to 4.5+/-2.5 in non-ischaemic areas (n=15), while in the ischaemic areas (n=5) AI increased (p<0.05) to 25.2+/-4.1. Since the spastic artery is intrinsically resistant to hypertension, the marked increase in CBF during hypertension can be attributable to ischaemia following SAH.