Summary
The closure of small airways in gravity-dependent lung regions (airway closure) is thought to be an important factor influencing ventilation-perfusion (v/q) relationships. Airway closure has been noted by other authors as predisposing to atelectasis, under appropriate circumstances.
We have assessed airway closure by a modified single breath nitrogen technique in ten normal male subjects in several surgical positions. Functional residual capacity (frc) was measured by a closed-circuit helium technique, to allow correlation of the airway closure findings with the alterations in lung volume associated with the posture changes. Functional consequences of airway closure are likely when the closing volume (the lung volume at which airway closure starts to occur) is abovefrc, with closure then occurring within the range of tidal breathing. Subjects were studied in the seated, supine, 15° head-down, and combined lithotomy plus 15° head-down position.
Airway closure was found to involve increasing lung volumes with increasing subjects’ ages, in agreement with previous observations. In the seated position the age at which the closing volume exceededfrc was 49 years. This age decreased to 36 in the supine position, 35.5 head-down, and 32 in the combined lithotomy and head-down position. Body position, therefore, has an important effect on the critical relationship between the closing volume andfrc, and hence on the functional consequences of airway closure. *** DIRECT SUPPORT *** A00LO001 00003
Résumé
La fermeture des voies aériennes dans les régions pulmonaires en position déclive (fermeture des bronchioles) est, dit-on, un facteur important influençant la relation ventilation/perfusion v/Q. La fermeture des voies aériennes, au dire d’autres auteurs, prédispose à l’atélectasie dans certaines circonstances.
Chez dix sujets mâles normaux, placés en diverses positions chirurgicales, nous avons évalué la fermeture des voies aériennes par une technique modifiée d’une seule respiration d’azote. Nous avons mesuré la capacité fonctionnelle résiduelle (cfr) par une technique à circuit fermé avec hélium afin de permettre d’établir une correlation entre les résultats obtenus de la fermeture des voies aériennes et les modifications du volume pulmonaire attribuables aux changements de position. Les conséquences fonctionnelles de la fermeture des voies aériennes surviennent lorsque le volume de fermeture dépasse lacfr (le volume pulmonaire auquel commence la fermeture des voies aériennes) alors que la fermeture apparaissant est de l’ordre de l’air courant. Nous avons étudié les sujets en position assise, couchée, la tête baissé de 15° et la position de lithotomie associée à un Trendelenbourg de 15°.
En accord avec des observations antérieures, la fermeture des voies aériennes s’est étendue à des surfaces pulmonaires augmentant avec l’âge des sujets. En position assise, l’âge auquel la fermeture des voies aériennes dépassait lasfr était de 49 ans. En position dorsale, l’âge s’abaissait à 36 ans, en Trendelenbourg, à 35.5 et dans la position associée Trendelenbourg et lithotomie, à 32 ans. En conséquence, la position du corps joue un rôle important sur la relation critique entre la fermeture des voies aériennes et lacfr et, de là sur les conséquences fonctionnelles de la fermeture des voies aériennes.
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An erratum to this article is available at http://dx.doi.org/10.1007/BF03026224.
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Craig, D.B., Wahba, W.M. & Don, H. Airway closure and lung volumes in surgical positions. Canad. Anaesth. Soc. J. 18, 92–99 (1971). https://doi.org/10.1007/BF03025430
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DOI: https://doi.org/10.1007/BF03025430