Hyperventilation during exercise: Independence on exercise-induced bronchoconstriction in mild asthma

Ventilatory gas exchange during exercise was compared in patients with mild asthma (11 females and 11 males), hyperventilation syndrome (HVS, 11 females), and healthy subjects (11 females and 11 males) in order to assess hyperventilation during exercise and its association with exercise-induced bronchoconstriction. The asthmatics showed decreased working capacity and decreased maximal oxygen consumption, with no evidence of limitation due to impairment of ventilatory capacity. Ventilatory equivalents for CO2 and O-2 (Vover dotE/Vover dotCO(2) and Vover dotE/Vover dotO(2)) at rest did not differ between the controls and asthmatics, but they were significantly elevated in HVS. In female asthmatics, ventilatory equivalents during exercise were significantly (P<0.05) elevated compared with those of healthy subjects; in female controls, Vover dotE/Vover dotCO(2) was 30.1 +/- 3.3 at low exercise and 27.4 +/- 6.5 at maximal exercise. In female asthmatics, the corresponding figures were 34.9 +/- 6.1 and 36.7 +/- 5.3. Furthermore, Vover dot/Vover dotCO(2) individually related to percent of maximal oxygen consumption (Vover dotO(2 max) was significantly increased in female asthmatics both at low and high Vover dotO(2). The highest ventilatory equivalents were obtained in HVS, 41.7 +/- 6.7 and 43.9 +/- 0.9, respectively. Significant exercise-induced bronchoconstriction (decrease of FEV(1) >15%) was found in 50% of the asthmatics. The ventilatory equivalents did not correlate with exercise-induced changes in FEV(1) (r(2)<0.3). Mild exercise-induced hyperventilation which was observed in mild female asthmatics, did not appear to be related to exercise-induced bronchoconstriction.