Shimoda L A, Norins N A, Madden J A
Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin, USA.
Pediatr Res. 1998 Apr;43(4 Pt 1):514-20. doi: 10.1203/00006450-199804000-00013.
Because cerebrovascular hemorrhage in newborns is often associated with fluctuations in cerebral blood flow, this study was designed to investigate the effects of pulsatile flow in isolated cerebral arteries from neonatal piglets. Arteries mounted on cannulas were bathed in and perfused with a physiologic saline solution. An electronic system produced pulsations, the amplitude and frequency of which were independently controlled. At constant mean transmural pressure (20 mm Hg), increasing flow in steps from 0 to 1.6 mL/min under steady flow conditions caused a biphasic response, constriction at low flow, and dilation at high flow. Under pulsatile flow conditions (pulse amplitude 16-24 mm Hg; 2 Hz), the arteries dilated upon flow initiation and continued to dilate as mean flow increased. Dilation to pulsatile flow did not depend on the level of mean flow because switching from steady to pulsatile flow at each flow step also caused dilation. Arteries dilated further upon increasing either pulse amplitude (12-28 mm Hg; 2 Hz) or frequency (16-24 mm Hg; 4 Hz). Inhibiting nitric oxide synthesis with Nomega-nitro-L-arginine or perfusing with glutaraldehyde to decrease endothelial cell deformability significantly reduced dilations to pulsatile flow and to increased amplitude and frequency. These data suggest that the arterial response to flow is highly dependent on the mode of flow. Dilation induced by initiating pulsatile flow or increasing either pulse amplitude or frequency appears to be mediated by augmented nitric oxide release as result of shear stress-induced deformation of the endothelial cells.
由于新生儿脑血管出血常与脑血流波动有关，本研究旨在探讨脉动流对新生仔猪离体脑动脉的影响。安装在插管上的动脉浸泡在生理盐溶液中并进行灌注。一个电子系统产生脉动，其幅度和频率可独立控制。在恒定平均跨壁压（20 mmHg）下，在稳定流条件下将流量从0逐步增加到1.6 mL/min会引起双相反应，低流量时收缩，高流量时扩张。在脉动流条件下（脉冲幅度16 - 24 mmHg；2 Hz），动脉在开始流动时扩张，并随着平均流量增加而持续扩张。对脉动流的扩张不依赖于平均流量水平，因为在每个流量步骤从稳定流切换到脉动流也会引起扩张。当增加脉冲幅度（12 - 28 mmHg；2 Hz）或频率（16 - 24 mmHg；4 Hz）时，动脉会进一步扩张。用Nω-硝基-L-精氨酸抑制一氧化氮合成或用戊二醛灌注以降低内皮细胞可变形性，可显著减少对脉动流以及对增加幅度和频率的扩张。这些数据表明动脉对血流的反应高度依赖于血流模式。由启动脉动流或增加脉冲幅度或频率引起的扩张似乎是由剪切应力诱导的内皮细胞变形导致一氧化氮释放增加所介导的。
