Toyoda K, Fujii K, Ibayashi S, Sadoshima S, Fujishima M
Second Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Am J Physiol. 1996 Apr;270(4 Pt 2):H1350-4. doi: 10.1152/ajpheart.1996.270.4.H1350.
Cerebral arterioles have been regarded as the primary sites of autoregulatory responses, whereas the role of large arteries in the cerebral autoregulation is poorly understood. The goal of this study was to determine in vivo whether the basilar artery and its primary branches act as resistance vessels under hypotensive conditions by simultaneously measuring their diameters and local brain stem blood flow with laser-Doppler flowmetry. In 10 anesthetized rats, blood flow to the brain stem was well maintained during stepwise hemorrhagic hypotension when mean arterial blood pressure fell from 116 +/- 3 to 50 mmHg and decreased gradually between 50 and 30 mmHg. Diameter of the basilar artery (n = 10) and its large branches (n = 22), measured through an open cranial window, increased by 10% from the baseline value at 50 mmHg and reached their maximum at 30 mmHg (314 +/- 9 from 244 +/- 6 mum, and 149 +/- 4 from 117 +/- 3 mum, respectively). Small branches (n = 15) dilated to a larger extent compared with the larger arteries throughout hypotension and reached the maximum at 30 mmHg (69 +/- 3 from 48 +/- 2 mum). Below 30 mmHg, there was a steep fall in blood flow and reduction in diameter of all-sized arteries. Thus small vessels contribute to reductions in cerebrovascular resistance throughout the entire autoregulatory-range in the brain stem circulation. Large arteries, such as the basilar artery and its branches, also contribute to reductions in cerebrovascular resistance around the lower limits of cerebral blood flow autoregulation and may thus play a significant role in maintaining blood flow to the brain stem during severe systemic hypotension.
脑小动脉一直被视为自身调节反应的主要部位，而大动脉在脑自身调节中的作用却知之甚少。本研究的目的是通过激光多普勒血流仪同时测量基底动脉及其主要分支的直径和局部脑干血流，来确定在低血压条件下基底动脉及其主要分支在体内是否作为阻力血管发挥作用。在10只麻醉大鼠中，当平均动脉血压从116±3 mmHg逐步降至50 mmHg时，脑干血流在出血性低血压过程中得到良好维持，且在50至30 mmHg之间逐渐下降。通过开放的颅骨窗口测量，基底动脉（n = 10）及其大分支（n = 22）的直径在50 mmHg时较基线值增加了10%，并在30 mmHg时达到最大值（分别从244±6 µm增加到314±9 µm，从117±3 µm增加到149±4 µm）。在整个低血压过程中，小分支（n = 15）的扩张程度比大血管更大，并在30 mmHg时达到最大值（从48±2 µm增加到69±3 µm）。低于30 mmHg时，所有大小动脉的血流均急剧下降，直径减小。因此，在脑干循环的整个自身调节范围内，小血管有助于降低脑血管阻力。像基底动脉及其分支这样的大动脉，在脑血流自身调节下限附近也有助于降低脑血管阻力，因此在严重全身性低血压期间可能在维持脑干血流方面发挥重要作用。
