Curran-Everett D C, Meredith M P, Krasney J A
Department of Physiology, School of Medicine, State University of New York, Buffalo.
Respir Physiol. 1992 Jun;88(3):355-71. doi: 10.1016/0034-5687(92)90009-l.
Ventilatory acclimatization (VA) to hypoxia alters cerebrovascular responses to arterial blood gas perturbations. For example, after VA, cerebral blood flow (CBF) is elevated, at a given arterial CO2 tension (PaCO2), compared to CBF before VA. This experiment examined the effects of VA to 72 h of normobaric hypoxia [arterial O2 tension (PaO2) approx. 40 mmHg, O2 saturation in arterial blood approx. 50%] on total and regional cerebrovascular resistance (CVR and rCVR) and cerebral O2 extraction fraction (OEF) in 32 conscious sheep. Four different O2-CO2 gas combinations were sequentially administered to each sheep before and after VA. CVR and rCVR were calculated from CBF (radiolabeled microspheres) and arterial and cerebral downstream pressures; OEF was calculated from arterial and cerebral venous O2 contents. After VA, during hyperoxia, CVR and rCVR tended to be lower during both hypocapnia and hypercapnia. During hypoxia, although CVR and rCVR were slightly less during hypocapnia, CVR and rCVR during hypercapnia were surprisingly increased. The post-VA increases in mean CVR and mean rCVR during hypoxic gas combinations differed from the post-VA decreases during hyperoxic gas combinations (0.04 less than or equal to P less than or equal to 0.11). In contrast, although VA decreased OEF during three of four gas combinations (P less than or equal to 0.003), there was a greater mean post-VA decrease in OEF during hypercapnic gas combinations than during hypocapnic gas combinations (P = 0.025); decreases in OEF were correlated with decreases in cerebral O2 consumption. The post-VA CVR responses may reflect altered neurocirculatory control by the arterial chemoreflex; the OEF responses suggest relative cerebral hyperperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)
通气适应低氧（VA）会改变脑血管对动脉血气扰动的反应。例如，通气适应后，在给定的动脉二氧化碳分压（PaCO2）下，脑血流量（CBF）比通气适应前升高。本实验研究了32只清醒绵羊通气适应72小时常压低氧[动脉血氧分压（PaO2）约40 mmHg，动脉血氧饱和度约50%]对总脑血管阻力和局部脑血管阻力（CVR和rCVR）以及脑氧摄取分数（OEF）的影响。在通气适应前后，依次给每只绵羊施用四种不同的氧 - 二氧化碳气体组合。CVR和rCVR根据CBF（放射性微球）以及动脉和脑下游压力计算得出；OEF根据动脉和脑静脉血氧含量计算得出。通气适应后，在高氧期间，低碳酸血症和高碳酸血症时CVR和rCVR均趋于降低。在低氧期间，虽然低碳酸血症时CVR和rCVR略有降低，但高碳酸血症时CVR和rCVR却惊人地增加。低氧气体组合时通气适应后平均CVR和平均rCVR的增加与高氧气体组合时通气适应后的降低不同（0.04≤P≤0.11）。相比之下，虽然通气适应在四种气体组合中的三种情况下降低了OEF（P≤0.003），但高碳酸血症气体组合时通气适应后OEF的平均降低幅度大于低碳酸血症气体组合时（P = 0.025）；OEF的降低与脑氧消耗的降低相关。通气适应后的CVR反应可能反映了动脉化学反射对神经循环控制的改变；OEF反应表明存在相对的脑血流灌注过多。（摘要截短至250字）
