Increased BMI predisposes to airway closure during bronchoconstriction
Waist circumference (WC) may have restrictive effects on baseline lung function, but it is increased BMI, rather than WC, that contributes to airway closure during bronchoconstriction, according to a study.
Methacholine challenge was performed in 116 asthmatic patients, 56 of which were obese. An inverse association existed between spirometric lung function and WC (p<0.05), but not BMI. Closing index significantly increased during bronchoconstriction in obese patients and was associated with increased BMI (p=0.01), rather than WC.
On the other hand, sensitivity to airway closure and narrowing did not have any association with BMI or WC.
These results indicate that obesity has a significant impact on airway closure during bronchoconstriction through mechanisms other than simple mass loading, according to the authors.
Participants in this study underwent both spirometry and methacholine challenge. The authors evaluated sensitivity to airway closure and narrowing from the dose–response slopes of the forced vital capacity (FVC) and the ratio of forced expiratory volume in 1 s (FEV1) to FVC, respectively. They also calculated airway closure during bronchoconstriction (closing index) as the percent reduction in FVC divided by the percent reduction in FEV1 at maximal bronchoconstriction.
“Obesity produces restrictive effects on lung function. We previously reported that obese patients with asthma exhibit a propensity towards small airway closure during methacholine challenge which improved with weight loss. We hypothesized that increased abdominal adiposity, a key contributor to the restrictive effects of obesity on the lung, mediates this response,” the authors said.