Lung function during and after prolonged head-down bed rest.
We determined the effects of prolonged head-down tilt bed rest (HDT) on lung mechanics and gas exchange. Six subjects were studied in supine and upright postures before (control), during [day 113 (D113)], and after (R + number of days of recovery) 120 days of HDT. Peak expiratory flow (PF) never differed between positions at any time and never differed from controls. Maximal midexpiratory flow (FEF(25-75%)) was lower in the supine than in the upright posture before HDT and was reduced in the supine posture by about 20% between baseline and D113, R + 0, and R + 3. The diffusing capacity for carbon monoxide corrected to a standardized alveolar volume (volume-corrected DL(CO)) was lower in the upright than in the supine posture and decreased in both postures by 20% between baseline and R + 0 and by 15% between baseline and R + 15. Pulmonary blood flow (Q(C)) increased from R + 0 to R + 3 by 20 (supine) and 35% (upright). As PF is mostly effort dependent, our data speak against major respiratory muscle deconditioning after 120 days of HDT. The decrease in FEF(25-75%) suggests a reduction in elastic recoil. Time courses of volume-corrected DL(CO) and Q(C) could be explained by a decrease in central blood volume during and immediately after HDT.
Montmerle
Stéphanie
S
Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden. stephanie.montmerle@fyfa.ki.se
Spaak
Jonas
J
Linnarsson
Dag
D
D000328:Adult; D001810:Blood Volume / Q000502:physiology; D002248:Carbon Monoxide / Q000378:metabolism; D006112:Gravitation; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D008297:Male; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012129:Respiratory Function Tests; D012146:Rest / Q000502:physiology*; D018474:Weightlessness Simulation
D002248:Carbon Monoxide