Mirro R, Karanth S, Armstead W M, Shibata M, Leffler C W
Department of Pediatrics, University of Tennessee, Memphis 38163.
Pediatr Res. 1992 Jul;32(1):114-7. doi: 10.1203/00006450-199207000-00022.
Pressure ventilation of the newborn can adversely affect the cardiovascular system. Increasing airway pressure increases cerebral venous pressure, thus stressing brain vasculature. To test the hypothesis that cerebral venous distension caused by mechanical ventilation alters cerebral microvascular responses, we studied cerebrovascular responses before, during, and after positive pressure ventilation. Anesthetized newborn pigs were ventilated with a standard time-cycled, pressure-limited infant respirator. Pial arterioles were measured in response to hypercapnia, topical isoproterenol, and topical norepinephrine during control [mean airway pressure (Paw) = 0.9 +/- 0.05 kPa (4.8 +/- 0.3 cm H2O)] conditions, during 40-60 min of increased Paw [2.5 +/- 0.2 kPa (13.9 +/- 1.3 cm H2O)], and when the Paw was lowered again. Pial arteriolar dilation in response to hypercapnia was not changed by increasing Paw. Similarly, responses to isoproterenol and norepinephrine were unaltered during raised Paw. However, a significant decrease in responses to topical isoproterenol and norepinephrine was observed after increased Paw. These experiments show that specific prostanoid-independent cerebrovascular responses are altered subsequent to pressure ventilation, whereas prostanoid-dependent dilation to hypercapnia was not affected. These changes suggest that the newborn cerebral vasculature is affected by positive pressure ventilation, further raising the possibility that ventilation-induced alterations in microvascular responses could make the brain more vulnerable to added stresses after pressure ventilation.
新生儿的压力通气会对心血管系统产生不利影响。气道压力增加会使脑静脉压力升高，从而给脑血管系统造成压力。为了验证机械通气引起的脑静脉扩张会改变脑微血管反应这一假设，我们研究了正压通气前、通气期间和通气后的脑血管反应。用标准的时间循环、压力限制型婴儿呼吸机对麻醉后的新生猪进行通气。在对照条件下[平均气道压力（Paw）=0.9±0.05千帕（4.8±0.3厘米水柱）]、Paw升高[2.5±0.2千帕（13.9±1.3厘米水柱）]的40 - 60分钟期间以及Paw再次降低时，测量软脑膜小动脉对高碳酸血症、局部应用异丙肾上腺素和局部应用去甲肾上腺素的反应。Paw升高并未改变软脑膜小动脉对高碳酸血症的扩张反应。同样，在Paw升高期间，对异丙肾上腺素和去甲肾上腺素的反应也未改变。然而，在Paw升高后，观察到对局部应用异丙肾上腺素和去甲肾上腺素的反应显著降低。这些实验表明，压力通气后，特定的不依赖前列腺素的脑血管反应发生了改变，而依赖前列腺素的对高碳酸血症的扩张反应未受影响。这些变化表明新生儿脑血管系统受到正压通气的影响，进一步增加了通气引起的微血管反应改变可能使大脑在压力通气后更容易受到额外应激影响的可能性。
