Exertional dyspnea and operating lung volumes in asthma

Abstract

Dyspnea has been reported to be a main contributor to exercise avoidance in asthma. While traditional markers of ventilation do not explain the heightened dyspnea during exercise in patients with asthma, this study proposed that exertional dyspnea in asthma was due to high-operating lung volumes, which may be improved with a short-acting β2-agonist. On two separate days, 16 patients with asthma and 16 controls completed a lung function test and incremental exercise tests to exhaustion. On one of the days (order randomized), 400 μg salbutamol was administered before exercise. Inspiratory capacity (IC), inspiratory reserve volume (IRV), and dyspnea (modified Borg scale) were evaluated throughout exercise. Compared with controls, patients with asthma reported greater dyspnea at the same absolute submaximal workloads. Furthermore, patients with asthma demonstrated altered breathing responses to exercise, characterized by reduced IC and IRV throughout exercise compared with controls. The reduced IRV was associated with increased dyspnea in patients with asthma. Salbutamol did not affect dyspnea or operating lung volumes in either group. The increased perception of dyspnea during incremental exercise in patients with asthma appears to be secondary to a reduction in IRV, which is unaffected by an inhaled β2-agonist.