Summary
Closing capacity (CC; the lung volume at which dependent lung zones cease to ventilate, presumably as a result of airway closure) and standard lung volumes were measured in twenty-four normal women 21 to 29 years of age in the seated and supine positions. Measurements were made serially during pregnancy and once 6 to 8 weeks post partum (the control period). CC was unchanged during pregnancy, while functional residual capacity (FRC) fell by approximately 15 per cent. The difference between FRC and CC (FRC-CC) was reduced during pregnancy, but in one of the subjects when seated, and in only two supine subjects did CC exceed FRC. FRC-CC was reduced in the supine position as compared to seated. The reduced FRC-CC during pregnancy offers a potential explanation for the observations of abnormally low arterial oxygen tensions (Pa02) during pregnancy in some women, and of reduced Pa02. in pregnant women in the supine as compared to upright position.
Résumé
La capacité de fermeture (volume où les parties déclives du poumon cessent d’étre ventilées, présumément par fermeture des voies aériennes) et les volumes pulmonaires standards ont été mesurés chez 24 femmes normales âgées de 21 à 29 ans, en position assise et couchée. Ces mesures ont été effectuées de façon sériée pendant la grossesse, et durant six-huit semaines en post-partum (péiode controle). La capacité de fermeture demeure inchangée durant la grossesse, alors que la FRC chute de 15 pour cent environ. L’écart entre la capacite de fermeture et la FRC (FRC-CC) est réduit durant la grossesse; chez l’une de ces patientes, en position assise, et chez deux autres en position couchee, la capacité de fermeture a excédé la FRC. La réduction de cet écart est plus importante en position couchée qu’en position assise. La réduction de l’écart entre la FRC et la capacité de fermeture, durant la grossesse, est une explication possible de la diminution de la tension en Oxygène du sang artériel (Pao2) observée durant la grossesse chez certaines patientes, et de la diminution de la Pa02 chez la femme enceinte en position couchee, comparee a la position debout.
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Craig, D.B., Toole, M.A. Airway closure in pregnancy. Canad. Anaesth. Soc. J. 22, 665–672 (1975). https://doi.org/10.1007/BF03013314
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DOI: https://doi.org/10.1007/BF03013314