Airway Function during Exercise in Asthmatics is Homogeneous Despite Heterogeneous Airway Function Prior to Exercise

Abstract

Variability in airway function is a principle characteristic of the asthmatic condition. The relationships between variable pre-exercise airway function and airway function during exercise in asthmatics, however, have not been determined. PURPOSE: The purpose of this study is to determine the effects of improved and worsened pre-exercise airway function on the pulmonary system responses to exercise in asthmatic subjects. METHODS: Mild-to-moderate asthmatics (currently, n=6) performed cycle exercise to exhaustion (∼85% peak power output) on four separate occasions. Prior to each exercise test, subjects completed one of four interventions in random order: 1) inhalation of a b2-agonist to improve airway function (BD), 2) voluntary eucapnic hyperpnea challenge to worsen airway function (BC), 3) placebo to the hyperpnea challenge (PL), and 4) a control trial of seated relaxation (CON). Metabolic rate, minute ventilation, and calculated pulmonary resistance (RL) (esophageal balloon technique) were assessed at rest and during exercise. RESULTS: The forced expiratory volume 1.0 sec was increased prior to exercise during BD and decreased prior to exercise during BC (4.0 vs. 3.1 L for BD vs. BC). Despite this, exercise time-to-exhaustion was similar during the four trials (CON, 5.5 ± 2; BD, 5.5 ± 2.5; BC, 5.6 ± 2.6; PL, 4.8 ± 1.6 min). Moreover, the ventilatory equivalent for CO2 production was similar during the four trials (CON, 35 ± 6; BD, 35 ± 3; BC, 36 ± 6; PL, 35 ± 5). Prior to exercise, RL was increased during BC compared with CON (3.1 ±.8 vs. 2.1 ± 1.1 cmH2O/L/sec for BC vs. CON). During BC exercise, however, RL decreased (indicating bronchodilation), and all exercise values for RL converged such that they were similar at end exercise during all four trials (CON, 2.0 ± 1.6; BD, 2.2 ± 1.4; BC, 2.2 ± 1.3; PL, 2.2 ± 1.4 cmH2O/L/sec). CONCLUSIONS: Thus far (n=6), worsening or improving airway function before exercise in asthmatic subjects has not affected the pulmonary system responses to whole-body exercise. These data support the hypothesis that airway function during exercise in asthmatics is homogeneous despite heterogeneous airway function prior to exercise. Moreover, exercise capacity in asthmatic subjects is independent of pre-exercise airway function. Supported by Vermont Genetics Network through P20 RR16462.