Influence of Body Fat on Exercise-Induced Bronchoconstriction

Abstract

The prevalence of obesity and asthma (including exercise-induced bronchoconstriction, EIB) are both increasing in the United States. While previous research suggests a link between obesity and EIB, the effect of body fat on airway hyper-reactivity following exercise is not known. PURPOSE: To determine the effect of body fat on airway function in subjects with EIB. METHODS: Thirteen subjects (4 men, 9 women) with EIB (determined by ≥10% decrease in FEV1 following an exercise bout and a eucapnic voluntary hyperventilation test: EVH) were divided into three groups (high fat HF, n=5; moderate fat MF, n=4; low fat LF, n=4) based on total body fat (g) relative to height (HF 161.4 ± 19.5; MF 117.5 ± 8.5; LF 63.5 ± 9.9 g/cm; p <0.05) determined via Dual Energy X-ray Absorptiometry (DXA; Lunar). Pulmonary function tests (PFT) and exhaled nitric oxide (ENO; Sievers) were determined in triplicate pre and post (min 5, 15, 30) exercise. Subjects completed a constant load eight minute exercise test on a cycle ergometer at a workload based on a target ventilation of ∼50–60% predicted maximal voluntary ventilation while breathing dry air. RESULTS: There were no differences (P > 0.05) between groups in PFT or ENO at rest, or in metabolic or ventilatory variables during exercise. However, the decrease in FEV1 from baseline to 5 minutes post exercise was less (p <0.05) in MF (−15.5 ± 1.4%) compared to both LF (−28.5 ± 6.6%) and HF (−31.2 ± 1.4%). Also, at 5 minutes post exercise, the decrease in ENO was significantly greater in HF (−18.6 ± 2.7%) vs. MF (−8.8 ± 2.5%). There was no difference (P > 0.05) at min 15 or 30 post exercise in any variable. CONCLUSION: These data suggest that, for our population, both high and low body fat lead to greater airway narrowing following exercise in subjects with EIB compared to subjects with moderate body fat amounts. The mechanism responsible may be a greater bronchoprotective role of airway nitric oxide in moderately fat individuals.