Repeat Exercise Normalizes the Gas-Exchange Impairment Induced by a Previous Exercise Bout in Asthmatic Subjects

Abstract

Purpose of the Study. To determine the effects of a second exercise bout on the gas-exchange impairment caused by an initial exercise-induced bronchospasm (EIB) response in asthmatic subjects. Study Population. Twenty-one subjects with a known history of asthma participated after meeting at least 1 inclusion criteria: (1) ≥12% increase in the forced expiratory volume in 1 second (FEV1) after β-agonist inhalation, (2) ≥10% decrease in FEV1 after exercise test to exhaustion, or (3) a provocative concentration ≤4.0 mg/mL of methacholine causing a 20% decrease in FEV1. Methods. The subjects performed 2 submaximal workloads for 3 minutes. After 3 to 5 minutes of rest, constant work-rate exercise was performed until exhaustion at 90% of maximal O2 uptake (EX1). Arterial blood and expired gases were collected at 3 (early recovery) and 35 (late recovery) minutes after EX1. Subjects then performed a second bout of exercise to exhaustion at 100% of maximal O2 uptake (EX2). Pulmonary-function tests were repeated at 5-minute intervals after EX1 and EX2. Results. Subjects classified as EIB+ (>10% FEV1 decrease 5–10 minutes after EX1) and EIB− had similar baseline lung function. In the EIB+ group, the inspiratory pulmonary resistance (RLi) peaked at 4.2 ± 3.2 cm H2O/L per second above baseline (P < .05) 4 minutes after EX1 and dropped back to baseline during EX2. The RLi did not change significantly in the EIB− group. After EX1, the EIB+ group showed a sustained decrease in FEV1 (2.8 ± 0.66 L versus baseline, 3.97 ± 0.47 L; P < .05), whereas the EIB− group did not (3.60 ± 0.56 L versus baseline, 3.72 ± 0.53 L). In the EIB+ group, the alveolar-to-arterial Po2 difference (A-aDo2) remained greater than baseline during early recovery after EX1 and widened to 14.1 mm Hg above baseline (P < .001) during late recovery. In the EIB− group, the A-aDo2 returned to baseline during early recovery and increased to 18.1 ± 9.1 mm Hg above baseline during late recovery. In both groups, the RLi, FEV1, and A-aDo2 were similar during EX1 and EX2. In the EIB+ group, sputum histamine increased after exercise (61.2 ± 42.0 ng/mL versus baseline 34.6 ± 25.9 ng/mL; P < .05) and was correlated with the A-aDo2 (r = 0.68; P = .02) during EX1. Conclusions. In asthmatic patients, late gas-exchange disturbance after exercise occurs independently of decreased FEV1 or increased pulmonary resistance. Gas exchange normalizes with a second bout of exercise, likely because of bronchodilation. Reviewer Comments. A new finding from this study is the gas-exchange impairment seen after exercise in asthmatic patients without measurable disturbance in FEV1 or pulmonary resistance after exercise; this late-recovery impairment of gas exchange may be a result of peripheral airway abnormalities that take time to develop. As expected, sputum inflammatory mediators were increased in patients with EIB. One of the goals of asthma management is to avoid restrictions on activity and exercise, and the normalization of lung function and gas exchange seen in most subjects with a second bout of exercise offers some reassurance to asthmatic patients involved in repetitive, intense physical activity.