STATIC LUNG LOAD AND POSTURE EFFECTS ON PULMONARY MECHANICS AND COMFORT IN UNDERWATER EXERCISE

Static lung load (SLL), or transrespiratory pressure gradient, imposed by underwater breathing apparatus can affect breathing comfort and me chanics, especially during exertion. We examined the effects of body p osition and SLL on two factors known to affect or limit exertion: a) t idal flow-volume limitation, i.e., the percentage of the tidal volume that meets the boundary of the maximum expiratory flow-volume curve; a nd b) breathing discomfort. Eight healthy male scuba divers (28 +/- 4 yr) performed cycle ergometry to exhaustion during immersion in each o f four combinations of body position and SLL: upright, prone, + 10 cmH 2O, - 10 cmH2O.SLL was referenced to the sternal notch. Tidal flow-vol ume limitation was significantly greater with the negative SLL (P < 0. 05). In the prone position, higher expiratory flows were achieved (P < 0.01) and flow limitation was not significantly increased. Respirator y discomfort was quantified with a psychophysical rating scale and inc reased significantly as exercise intensity increased (P < 0.01). No ef fect of posture or SLL on discomfort was found. We conclude that, alth ough respiratory comfort is unaffected, positive static lung loading a nd the prone body position minimize adverse changes in respiratory mec hanics during exercise in immersion.