Sikkes B P, Manohar M, Duren S E, Day J, Baker J P
Department of Animal Sciences, College of Agriculture, University of Kentucky, Lexington 40546.
Am J Vet Res. 1992 Oct;53(10):1868-72.
Experiments were carried out on 8 healthy ponies to examine the effects of prolonged submaximal exercise on regional distribution of brain blood flow. Brain blood flow was ascertained by use of 15-microns-diameter radionuclide-labeled microspheres injected into the left ventricle. The reference blood was withdrawn from the thoracic aorta at a constant rate of 21.0 ml/min. Hemodynamic data were obtained with the ponies at rest (control), and at 5, 15, and 26 minutes of exercise performed at a speed setting of 13 mph on a treadmill with a fixed incline of 7%. Exercise lasted for 30 minutes and was carried out at an ambient temperature of 20 C. Heart rate, mean arterial pressure, and core temperature increased significantly with exercise. With the ponies at rest, a marked heterogeneity of perfusion was observed within the brain; the cerebral, as well as cerebellar gray matter, had greater blood flow than in the respective white matter, and a gradually decreasing gradient of blood flow existed from thalamus-hypothalamus to medulla. This pattern of perfusion heterogeneity was preserved during exercise. Regional brain blood flow at 5 and 15 minutes of exercise remained similar to resting values. However, at 26 minutes of exercise, vasoconstriction resulted in a significant reduction in blood flow to all cerebral and brain-stem regions. In the cerebellum, the gray matter blood flow and vascular resistance remained near control values even at 26 minutes of exercise. Vasoconstriction in various regions of the cerebrum and brainstem at 26 minutes of exertion may have occurred in response to exercise-induced hypocapnia, arterial hypertension, and/or sympathetic neural activation.
对8匹健康小马进行了实验，以研究长时间次最大运动对脑血流区域分布的影响。通过将直径为15微米的放射性核素标记微球注入左心室来确定脑血流。以21.0毫升/分钟的恒定速率从胸主动脉抽取参考血样。在小马休息时（对照）以及在跑步机上以13英里/小时的速度、7%的固定坡度进行运动的5分钟、15分钟和26分钟时获取血流动力学数据。运动持续30分钟，在20摄氏度的环境温度下进行。运动时心率、平均动脉压和核心温度显著升高。在小马休息时，观察到脑内灌注存在明显的异质性；大脑以及小脑灰质的血流比各自的白质更多，并且从丘脑 - 下丘脑到延髓存在血流逐渐降低的梯度。这种灌注异质性模式在运动过程中得以保留。运动5分钟和15分钟时的局部脑血流与静息值相似。然而，在运动26分钟时，血管收缩导致所有大脑和脑干区域的血流显著减少。在小脑中，即使在运动26分钟时，灰质血流和血管阻力仍接近对照值。在运动26分钟时大脑和脑干各区域的血管收缩可能是对运动诱导的低碳酸血症、动脉高血压和/或交感神经激活的反应。
