Adamson S L, Richardson B S, Homan J
J Appl Physiol (1985). 1987 Mar;62(3):989-98. doi: 10.1152/jappl.1987.62.3.989.
The role of umbilical cord occlusion in the initiation of breathing at birth was investigated using unanesthetized fetal sheep that were provided with access to a tracheal supply of hyperoxic air. Near-term fetuses were studied in utero to eliminate extraneous sensory stimuli. Gasping movements began 1.4 +/- 0.1 min after cord occlusion. Breathing was irregular for several minutes before continuous breathing (greater than or equal to 40 min-1) began 6 +/- 1 min after cord occlusion (n = 10). Arterial PO2 rose significantly from 18 +/- 2 mmHg before occlusion and was 115 +/- 15 mmHg immediately before cord release at 15 or 30 min. Breathing continued even during high-voltage electrocortical activity. Cord release caused the breathing rate to decrease from 77 +/- 13 min-1 during the last 5 min of cord occlusion to 5 +/- 3 min-1 10 min after cord release (P less than 0.002; n = 7). Results indicate the change from placental to lung gas exchange can occur in the absence of sensory and thermal changes normally present at birth and that the transition is reversible.
利用未麻醉的胎羊研究了脐带闭塞在出生时启动呼吸中的作用，这些胎羊可通过气管获得高氧空气。研究近足月胎儿在子宫内的情况以消除无关的感觉刺激。脐带闭塞后1.4±0.1分钟开始出现喘息动作。在脐带闭塞后6±1分钟开始持续呼吸（≥40次/分钟）之前，呼吸不规则持续了几分钟（n = 10）。动脉血氧分压在闭塞前从18±2 mmHg显著升高，在15或30分钟脐带松开前即刻为115±15 mmHg。即使在高电压皮层电活动期间呼吸仍持续。脐带松开导致呼吸频率从脐带闭塞最后5分钟时的77±13次/分钟降至脐带松开后10分钟时的5±3次/分钟（P<0.002；n = 7）。结果表明，从胎盘气体交换到肺气体交换的转变可以在没有出生时通常存在的感觉和热变化的情况下发生，并且这种转变是可逆的。
