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

¶ 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.