title: Gas exchange under altered gravitational stress.
abstract: Efficient gas exchange in the lung depends on the matching of ventilation and perfusion. However, the human lung is a readily deformable structure and as a result gravitational stresses generate gradients in both ventilation and perfusion. Nevertheless, the lung is capable of withstanding considerable change in the applied gravitational load before pulmonary gas exchange becomes impaired. The postural changes that are part of the everyday existence for most bipedal species are well tolerated, as is the removal of gravity (weightlessness). Increases in the applied gravitational load result only in a large impairment in pulmonary gas exchange above approximately three times that on the ground, at which point the matching of ventilation to perfusion is so impaired that efficient gas exchange is no longer possible. Much of the tolerance of the lung to alterations in gravitation stress comes from the fact that ventilation and perfusion are inextricably coupled. Deformations in the lung that alter ventilation necessarily alter perfusion, thus maintaining a degree of matching and minimizing the disruption in ventilation to perfusion ratio and thus gas exchange.
authors.affiliation: Departments of Medicine and Radiology, University of California, San Diego, USA. kprisk@ucsd.edu
authors.forename: G Kim
authors.initials: GK
authors.lastname: Prisk
mesh_terms: D000818:Animals; D006112:Gravitation; D006801:Humans; D018471:Hypergravity; D011187:Posture / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D013312:Stress, Physiological / Q000502:physiology*; D014692:Ventilation-Perfusion Ratio / Q000502:physiology; D014893:Weightlessness