title: [Closing volume of the respiratory airways and total lung capacity during 7-day antiorthostatic hypokinesis].
abstract: 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 degrees. By the 7th hour 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 less than 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 down 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 oxygen saturation of arterial blood.
mesh_terms: D000328:Adult; D003011:Closing Volume; D005652:Functional Residual Capacity; D006801:Humans; D007103:Immobilization; D008176:Lung Volume Measurements; D008297:Male; D010100:Oxygen / Q000097:blood; D011187:Posture; D013997:Time Factors; D014109:Total Lung Capacity; D014797:Vital Capacity
chemical_list: D010100:Oxygen
vernacular_title: "Ob'em zakrytiia" dykhatel'nykh puteĭ i struktura obsheĭ emkosti legkikh vo vremia 7-sutochnoĭ antiortostaticheskoĭ gipokinezii.