Toung T J, Aizawa H, Traystman R J
Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-7834, USA.
J Appl Physiol (1985). 2000 Feb;88(2):655-61. doi: 10.1152/jappl.2000.88.2.655.
Mechanical ventilation with positive end-expiratory pressure (PEEP) may prevent venous air embolism in the sitting position because cerebral venous pressure (Pcev) could be increased by the PEEP-induced increase in right atrial pressure (Pra). Whereas it is clear that there is a linear transmission of the PEEP-induced increase in Pra to Pcev while the dog is in the prone position, the mechanism of the transmission with the dog in the head-elevated position is unclear. We tested the hypothesis that a Starling resistor-type mechanism exists in the jugular veins when the head is elevated. In one group of dogs, increasing PEEP linearly increased Pcev with the dog in the prone position (head at heart level, slope = 0.851) but did not increase Pcev when the head was elevated. In another group of dogs, an external chest binder was used to produce a larger PEEP-induced increase in Pra. Further increasing Pra increased Pcev only after Pra exceeded a pressure of 19 mmHg (break pressure). This sharp inflection in the upstream (Pcev)-downstream (Pra) relationship suggests that this may be caused by a Starling resistor-type mechanism. We conclude that jugular venous collapse serves as a significant resistance in the transmission of Pra to Pcev in the head-elevated position.
呼气末正压通气（PEEP）的机械通气可能会预防坐位时的静脉空气栓塞，因为PEEP引起的右心房压力（Pra）升高可使脑静脉压力（Pcev）升高。虽然很明显，当狗处于俯卧位时，PEEP引起的Pra升高会线性传导至Pcev，但狗处于头高位时的传导机制尚不清楚。我们检验了这样一个假设，即当头抬高时，颈静脉中存在一种类似斯塔林电阻器的机制。在一组狗中，增加PEEP会使处于俯卧位（头部与心脏水平齐平，斜率 = 0.851）的狗的Pcev呈线性增加，但当头抬高时，Pcev并未增加。在另一组狗中，使用外部胸部束缚带使PEEP引起的Pra升高幅度更大。只有当Pra超过19 mmHg的压力（突破压力）后，进一步升高Pra才会使Pcev升高。上游（Pcev）-下游（Pra）关系中的这种急剧转折表明，这可能是由一种类似斯塔林电阻器的机制引起的。我们得出结论，在头高位时，颈静脉塌陷在Pra传导至Pcev的过程中起到了显著的阻力作用。
