Respiration physiology
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The increased alveolar-arterial oxygen gradient (A-aDO2) occurring at higher levels of exercise may reflect impaired gas mixing. This latter function was investigated using the multiple breath nitrogen washout technique in 30 physical training students (15 M, 15 F). They were examined at rest and at work loads of 50, 100 and 150 W, using a cycle ergometer. ⋯ Despite an increase in VDS from 156 +/- 33 to 258 +/- 35 ml and VDA from 139 +/- 40 to 305 +/- 73 ml, AME rose significantly with exercise from 72.5 +/- 5.0 to 78.3 +/- 3.3%. These results are discussed in relation to the morphology of the lung, and the stationary interface theory. They suggest that gas mixing improves at the onset of exercise only, so that the widening in A-aDO2 with increasing levels of exercise cannot be explained by impaired mixing efficiency alone, and is probably due to other factors such as critically rapid transit time of blood through the pulmonary capillaries as cardiac output increases.
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Respiration physiology · Dec 1991
Decreased pulmonary distensibility and pulmonary barotrauma in divers.
Pulmonary distensibility, lung volume and conductance were measured in 14 men (mean age 22 (SD 3) years) who suffered pulmonary barotrauma (PBT) during shallow water diving. Exponential analysis of static pressure-volume date obtained during deflation of the lungs gave K, and index of distensibility. The pulmonary conductance-recoil pressure (GL-PL) relationship was also obtained during deflation. ⋯ Decreased K reflects a decreased airspace size. Smaller airspaces increase the surface component of recoil pressure which increases the stress in tissue fibres. Relatively stiff airways may magnify the elastic stresses in peribronchial alveolar tissue increasing the possibility of rupture of alveolar walls with interstitial gas dissection.