Pulmonary function after actual and simulated exercise

Exercise alters pulmonary function and respiratory muscle strength in healthy humans. One explanation for these changes is fatigue of the respiratory muscles caused by the exercise, but the diaphragm produces little of the metabolites often associated with muscle fatigue. Recently, it was shown that there are different respiratory muscle responses to exercise and hyperpnea. Therefore, in this study we measured pulmonary function and respiratory muscle strength following maximal exercise or voluntary hyperpnea that simulated the ventilation seen during the exercise bout. Seven subjects had FVC, FEV_1.0, PImax, PEmax, and handgrip measured before and after an incremental maximal test on a cycle ergometer. The same variables were measured prior to and following a bout of voluntary hyperpnea in which tidal volume and breathing frequency were controlled to the same levels as during the exercise test, and before and following a period of rest of equal duration to the exercise and hyperpnea tests. FVC was decreased by 300 ml (6%, p<0.05) immediately following exercise, but returned to pre-exercise values within five minutes. PImax was decreased by 12 mmHg (15%) following exercise (p<0.005) and remained depressed after 15 minutes, recovering only 35% of the loss. None of the other variables were effected by exercise and none were altered during the control and hyperpnea bouts. These data indicate that pulmonary function and respiratory muscle strength are changed following exercise but not similar bouts of hyperpnea without accompanying exercise. Therefore, exercise affects pulmonary function independent of the respiratory muscle work done.