Rise I R, Kirkeby O J
Institute for Surgical Research, National Hospital, University of Oslo, Norway.
Acta Neurochir (Wien). 1998;140(7):699-705; discussion 705-6. doi: 10.1007/s007010050165.
Reports studying the combination of low blood pressure and cerebral ischaemia are few, and it remains to be determined how cerebral circulatory insufficiency modifies the cerebral perfusion and the central haemodynamic response to blood loss. We hypothesised that occlusion of arteries to the brain modifies the cerebrovascular and cardiovascular responses to blood loss. Continuous measurements of the cerebral microcirculation with laser Doppler microprobes in the cerebral cortex were performed in anaesthetised pigs during cerebral ischaemia and haemorrhagic hypotension. The response to rapid bleeding (25% of the blood volume) was recorded during normal conditions and during cerebral ischaemia induced by bilateral occlusion of the common carotid arteries. During normal conditions haemorrhage caused insignificant decreases in cerebral microcirculation. Haemorrhage during bilateral carotid artery occlusion, however, caused significantly greater changes in cerebral microcirculation and a greater posthaemorrhagic increase in cerebrovascular resistance shortly after the blood loss. Haemorrhage during bilateral carotid artery occlusion also caused greater reductions in cardiac output and arterial pressure than similar blood loss caused during normal conditions. This study showed a disproportionate decrease in cerebral blood flow with haemorrhage during bilateral carotid occlusion, caused by an immediate increase in cerebrovascular resistance. The results suggest that even a moderate blood loss in patients with impaired cerebral circulation could be dangerous, because normal compensatory mechanisms to haemorrhage are impaired.
研究低血压与脑缺血相结合情况的报告较少，脑循环功能不全如何改变脑灌注以及对失血的中枢血流动力学反应仍有待确定。我们假设大脑动脉闭塞会改变脑血管和心血管对失血的反应。在麻醉猪的脑缺血和失血性低血压期间，使用激光多普勒微探头对大脑皮层的脑微循环进行连续测量。在正常情况下以及双侧颈总动脉闭塞诱导的脑缺血期间，记录对快速失血（血容量的25%）的反应。在正常情况下，出血导致脑微循环的下降不明显。然而，双侧颈动脉闭塞期间的出血，在失血后不久导致脑微循环的变化明显更大，并且出血后脑血管阻力的增加更大。双侧颈动脉闭塞期间的出血也比正常情况下类似失血导致的心输出量和动脉压下降更大。这项研究表明，双侧颈动脉闭塞期间出血导致脑血流量不成比例地减少，这是由脑血管阻力立即增加所致。结果表明，即使是脑循环受损患者的中度失血也可能很危险，因为对出血的正常代偿机制受损。
