Airway obstruction during exercise and isocapnic hyperventilation in asthmatic subjects

We compared pulmonary mechanics measured during long-term exercise (LTX = 2 0 min) with long-term isocapnic hyperventilation (LTIH = 20 min) in the sam e asthmatic individuals (n = 6). Peak expiratory flow (PEF) and forced expi ratory volume in 1 s (FEV1) decreased during LTX (-19.7 and -22.0%, respect ively) and during LTIH (-6.66 and 10.9%, respectively). In contrast, inspir atory pulmonary resistance (RLI) was elevated during LTX (57.6%) but not du ring LTIH (9.62%). As expected, airway function deteriorated post-LTX and p ost-LTIH (FEV1 = -30.2 and -21.2%; RLI = 111.8 and 86.5%, respectively). We conclude that the degree of airway obstruction observed during LTX is of a greater magnitude than that observed during LTIH. Both modes of hyperpnea induced similar levels of airway obstruction in the posthyperpnea period. H owever, the greater airway obstruction during LTX suggests that a different process may be responsible for the changes in airway function during and a fter the two modes of hyperpnea. This finding raises questions about the eq uivalency of LTIH and LTX in the study of airway function during exercise-i nduced asthma.