Quantitative measurement of regional cerebral perfusion pressure and evaluation of autoregulatory function for cerebral blood flow

脑血管疾病患者维持脑血流量(CBF)和灌流压的自我调节机制可能受损。为探讨脑血管疾病患者脑循环损害的临界血流动力学状态，测定了乙酰唑胺(ACZ)对脑血管疾病患者局部脑血流量(CBF)和动脉/毛细血管血容量(Vo)的影响，以及以CBF/Vo比值为指标的血流动力学参数的变化，并期望其与局部灌流压成正比。对单侧大脑大动脉闭塞症患者分别于用药前及用药后10min行H^215O-PET检查，计算CBF、Vo及CBF/Vo比值。获得双侧大脑中动脉区域的血流动力学参数，并比较两个半球和两种情况下的血流动力学参数。使用ACZ后，同侧大脑半球CBF反应降低的患者组(=血管扩张能力降低组)在同一区域的Vo显著增加。因此，在血管扩张能力降低的患者的同侧大脑半球应用ACZ后，CBF/Vo比率显著降低。这一比值在本组的对侧大脑半球和血管扩张能力正常的另一组中均无变化，表明其降低代表着严重的血流动力学损害和局部灌流压自动调节功能障碍。CBF/Vo比值的显著降低与血管扩张能力降低的患者发生卒中有关。ACZ激发后CBF/Vo比值的降低被认为代表脑血管疾病患者局部脑灌流压力的改变，反映了脑血管疾病患者的临界血流动力学状态。

Autoregulatory mechanism to keep cerebral blood flow (CBF) and perfusion pressure may be impaired in patients with cerebrovascular disease. To investigate the critical hemodynamic status in the impaired cerebral circulation, changes in regional CBF and arterial-to-capillary blood volume (Vo) induced by acetazolamide (ACZ) were measured in patients with cerebrovascular disease, as well as changes in hemodynamic parameter defined by CBF/Vo ratio, which is expected to be proportional to the regional perfusion pressure. Patients with unilateral major cerebral arterial occlusive disease underwent H^2 15O-PET at baseline and 10 min after ACZ administration to calculate CBF, Vo and CBF/Vo ratio. The hemodynamic parameters in the territories of bilateral middle cerebral arteries were obtained and compared between the two hemispheres and two conditions. Following ACZ administration, the group of patients who had a reduced CBF response in the ipsilateral hemisphere (= reduced vasodilatory capacity group) showed a significant Vo increase in the same region. Thus, the CBF/Vo ratio decreased significantly after ACZ administration in the ipsilateral hemisphere of patients with reduced vasodilatory capacity. This ratio did not change in the contralateral hemisphere of this group nor in the other group with normal vasodilatory capacity, suggesting that its reduction represented severe hemodynamic impairment and dysfunction of autoregulation for regional perfusion pressure. The significant decrease in CBF/Vo ratio was associated with strokes in patients of reduced vasodilatory capacity. The decrease in the CBF/Vo ratio after ACZ challenge is presumed to represent altered regional cerebral perfusion pressure reflecting a critical hemodynamic status in patients with cerebrovascular disease.