Closing volume of the respiratory airways and total lung capacity during 7-day antiorthostatic hypokinesis
Nikolaenko, E.M.; Katkov, V.E.; Gvozdev, S.V.; Chestukhin, V.V.; Volkova, M.I.; Berkovskaya, M.I.
Kosmicheskaia Biologiia i Aviakosmicheskaia Meditsina 17(6): 39-43
1983
ISSN/ISBN: 0321-5040 PMID: 6656185 Document Number: 212784
By mass spectrography and pneumotachography, structural variations in total lung capacity (TLC) were investigated in 7 test subjects during 7-day head-down tilt at -15.degree. By the 7th h of head-down tilt, TLC, vital lung capacity (VLC), functional residual capacity (FRC) and residual volume (RV) decreased significantly and closing volume (CV) increased insignificantly. The CV/FRC ratio grew from 0.82 .+-. 0.03 to 1.24 .+-. 0.08 (P < 0.01), indicating the closure of respiratory pathways in certain lung structures within the tidal volume. These changes in the TLC structure persisted till day 7 but the CV/FRC ratio fell to 1.01 .+-. 0.07. The above findings can clarify the mechanism responsible for a lower oxygenation of arterial blood in the head-down position. The expiratory closure of the airways within the tidal volume causes regional changes in alveolar ventilation and ventilation-perfusion relations and, consequently, a larger venous admixture and a smaller O2 saturation of arterial blood. [The mechanism of disturbed gas exchange and the adaptation of human pulmonary function to weightlessness is discussed.].