Résumé
BACKGROUND: Critical closing pressure (CCP) is recently thought to play a key role in cerebral blood flow autoregulation as an effective downstream pressure of cerebral circulation and can objectively reflect the cerebrovascular tone, namely the vascular smooth muscle contraction and diastole, which is subjected to dynamic modulation.OBJECTIVE: To dynamically assess the hypertension-induced damage of the contraction function of cerebral microvascular smooth muscles and its correlation with morphological changes based on CCP evaluation.DESIGN: Randomized controlled experiment.SETTING: Institute of Neural Science of Second Hospital Affiliated to Guangzhou Medical College and Department of Neurology, First Hospital Affiliated to Sun Yet-san University.MATERIALS: The experiment was carried out at the Laboratory of Physiological Science of Sun Yet-san University between July 2002 and August 2003. Totally 160 health male SD rats were randomized into control group and hypertension group with 80 rats in each group. METHODS: Stroke-prone renovas cular hyp ortonsive rats were established in rats of the hypertension group by bilateral renal artery occlusion with two clips. The rats in the control group were not subjected to the occlusion with other treatments identical to those of the hypertension group. At the time points of 2, 4, 6, 8, 10, 12, 14 and 16 weeks after operation, respectively, 10 rats were randomly selected from each of the two groups for determination of arterial pressure and CCP. After the measurements the frontal-parietal lobe was obtained from the anaesthetized rats and cut into slices for quantitative analysis of the morphological changes in cerebral microvessels.different postoperative time points.mean arterial pressure in hypertension group obviously increased from the 6th postoperative week with significant difference from that of the control after operation to a level significantly higher than that of the control group at postoperative 14 and 16 weeks [(63.75±7.43) vs (37.28±3.68) mm Hg and (67.37±15.57) vs (38.39t7.41) mm Hg, respectively, P ＜ 0.05].significance from that of the control group at the 8th postoperative week (Paverage arterial pressure and cerebral arteriole tunica media (r=0.906 93,0.811 36, respectively, P ＜ 0.05). The changes in CCP was more obvious in the early and advanced stages of blood pressure elevation, but not so manifest during obvious blood pressure increment, displaying an inverted S-shaped curve of changes (R2=0.996 2, P ＜ 0.05).CONCLUSION: Contraction of the cerebrovascular smooth muscles is enhanced with the dynamic increment of arterial pressure after the development of hypertension. Vascular tone increase is more manifest during the early and advanced stages of hypertension.
Résumé
Objective To establish a new practical method to assess the cerebral blood flow autoregulation. Methods We assessed the flow velociey of middle cerebral artery with transcranial Doppler and recorded invasively the blood presure simultaneonsly. Then on the basis of critical closing pressure (CCP), the lower limit of cerebral blood flow autoregulation and the blood flow resistance of arterioles were calculated.The data compared with the results generated by routine method. Results The lower limit of autoregulation working out by CCP was 70.88±24.05 mmHg, which was similar to the result measured by routine method. The lower limit of autoregulation and the arteriole resistance in RHR were significantly higher than those of normal controls, and highly relate to arterial blood pressure significantly, especially pulse pressure. Conclusions The physiology and pathology of cerebral blood flow can be evaluated conveniently and accurately by assessment of the lower limit of autoregulation and arterioles resistance with CCP.
Résumé
AIM:To study the effect of hypertensive arteriosclerosis on cerebral blood flow autoregulation (CBFA), and to introduce a new method to measure the lower limit. METHODS:The blood velocities and blood pressure was recorded simultaneously and the curves of CBFA were analyzed and classified into classical and non-classical pattern. The lower limit were determined by clinical closing pressure (CCP) and the curve CBFA. RESULTS:When the blood pressure was decreasing, the classical and non-classical pattern of the cerebral blood flow autoregulation were 25% and 75% respectively in normal SD rats, while they were 40.55% and 54.45% respectively in renovascular hypertensive rats (RHR). However, when the blood pressure was elevating, the classical and non-classical pattern were 76.47% and 23.53% respectively in SD rats, while they were all classical in RHR. Furthermore, in SD and RHR ras, the lower limits measured by CCP were well in accordance with that measured by CBFA. CONCLUSION:Hypertensive arteriosclerosis could influence the limits and the patterns of cerebral blood flow autoregulation. The lower limit of CBFA can be measured and analyzed by CCP.
Résumé
AIM: To study the effect of hypertensive arteriosclerosis on cerebral blood flow autoregulation (CBFA), and to introduce a new method to measure the lower limit. METHODS: The blood velocities and blood pressure was recorded simultaneously and the curves of CBFA were analyzed and classified into classical and non-classical pattern. The lower limit were determined by clinical closing pressure (CCP) and the curve CBFA. RESULTS: When the blood pressure was decreasing, the classical and non-classical pattern of the cerebral blood flow autoregulation were 25% and 75% respectively in normal SD rats, while they were 40.55% and 54.45% respectively in renovascular hypertensive rats (RHR). However, when the blood pressure was elevating, the classical and non-classical pattern were 76.47% and 23.53% respectively in SD rats, while they were all classical in RHR. Furthermore, in SD and RHR ras, the lower limits measured by CCP were well in accordance with that measured by CBFA. CONCLUSION: Hypertensive arteriosclerosis could influence the limits and the patterns of cerebral blood flow autoregulation. The lower limit of CBFA can be measured and analyzed by CCP.