INSPIRATORY MUSCLE PERFORMANCE RELATIVE TO THE VENTILATORY THRESHOLD IN HEALTHY-SUBJECTS

Inspiratory muscle performance, ventilation, and gas exchange were stu died during exercise in healthy subjects to look for typical changes o f pattern of contraction at the ventilatory threshold (VT). The steepe ning of the slope of carbon dioxide output (VCO2) vs oxygen uptake (VO 2) at the VT was accompanied by a nonlinear increase of the mean rate of esophageal pressure development (Pes/T(I)) vs the esophageal pressu re time index (PTIes) reflecting both the relative force (Pbreath/Pesm ax) and duration (T(I)/T(TOT)) required for inspiration. The esophagea l pressure time integral within one breath (Pbreath.dT(I)) was one of the best single predictors of the ventilatory equivalent for oxygen (V (E)/VO2) at the VT. Moreover, we presented inspiratory muscle load ind ices as a mirror image of breathing pattern, with the obvious advantag e that the ventilation component can be compared with better establish ed methods of presenting ventilatory output. Inspiratory muscle perfor mance during exercise should link the increased metabolic rate to vent ilatory output. We conclude that 1) there exists an inspiratory muscle threshold that is well correlated to commonly used gas exchange thres holds, and 2) the efficiency of ventilation and gas exchange during ex ercise could be linked to pressure and timing of inspiratory muscle co ntraction.