Delacourt C, Canet E, Bureau M A
Jeremy Rill Center and Pulmonary Research Center, Department of Pediatrics, Sherbrooke University, Quebec, Canada.
J Appl Physiol (1985). 1996 Mar;80(3):892-8. doi: 10.1152/jappl.1996.80.3.892.
Apneas are very common and normal in newborns but may become life threatening if they are not terminated appropriately. The aim of this study in newborn lambs was to investigate the influence on apnea termination of postnatal maturation, peripheral chemoreceptor function, and hypoxia. Apneas were induced by passive hyperventilation at varying inspired O2 fraction levels. The apnea termination threshold PCO2 (PATTCO2) was defined as the arterial PCO2 value at the first breath after the apnea. Three groups of awake intubated lambs were studied: 1) intact lambs tested at both 1 and 15 days of life, 2) intact 1-day-old lambs with central tissue hypoxia induced by CO inhalation, and 3) 1-day-old lambs with carotid body denervation (CBD). In individual lambs and regardless of age and carotid body function, there was a PO2-PCO2 response curve that was a determinant for the termination of an apnea. PATTCO2 invariably increased when arterial PO2 increased, regardless of age. During hypoxia and normoxia, PATTCO2 was significantly lower in 15-day-old lambs compared with 1-day-old lambs. No difference was seen during hyperoxia. PATTCO2 values were shifted to higher levels after carotid body removal. Finally, hypoxia induced by either a low inspired O2 fraction or CO inhalation consistently failed to induce a depressive effect on the PATTCO2 even in CBD lambs. In conclusion, in awake newborn lambs, the PCO2 level for apnea termination changed with postnatal age, and carotid body function was essential in lowering PATTCO2, thus protecting the lambs against prolonged apnea. Furthermore, hypoxia consistently failed to depress the reinitiation of breathing after apnea, even in CBD lambs.
呼吸暂停在新生儿中非常常见且属正常现象，但如果不能得到适当终止，可能会危及生命。本研究以新生羔羊为对象，旨在探究出生后成熟度、外周化学感受器功能和低氧对呼吸暂停终止的影响。通过在不同的吸入氧分数水平下进行被动过度通气来诱发呼吸暂停。呼吸暂停终止阈值PCO₂（PATTCO₂）定义为呼吸暂停后首次呼吸时的动脉PCO₂值。研究了三组清醒插管的羔羊：1）在出生1天和15天时均接受测试的完整羔羊；2）通过吸入CO诱导中枢组织缺氧的1日龄完整羔羊；3）颈动脉体去神经支配（CBD）的1日龄羔羊。在个体羔羊中，无论年龄和颈动脉体功能如何，都存在一条PO₂-PCO₂反应曲线，它是呼吸暂停终止的决定因素。无论年龄大小，当动脉PO₂升高时，PATTCO₂总是会升高。在低氧和常氧期间，15日龄羔羊的PATTCO₂显著低于1日龄羔羊。在高氧期间未观察到差异。去除颈动脉体后，PATTCO₂值向更高水平偏移。最后，即使在CBD羔羊中，低吸入氧分数或吸入CO诱导的低氧也始终未能对PATTCO₂产生抑制作用。总之，在清醒的新生羔羊中，呼吸暂停终止的PCO₂水平随出生后年龄而变化，颈动脉体功能对于降低PATTCO₂至关重要，从而保护羔羊免受长时间呼吸暂停的影响。此外，即使在CBD羔羊中，低氧也始终未能抑制呼吸暂停后呼吸的重新启动。
