BMI but not central obesity predisposes to airway closure during bronchoconstriction

Abstract

Background and objective: 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. This study investigates the effect of body mass index (BMI) versus waist circumference (WC) on spirometric lung function, sensitivity to airway narrowing and closure, and airway closure during bronchoconstriction in patients with asthma. Methods: Participants underwent spirometry and methacholine challenge. Sensitivity to airway closure and narrowing was assessed from the dose-response slopes of the forced vital capacity (FVC) and the ratio of forced expiratory volume in 1 s (FEV 1 ) to FVC, respectively. Airway closure during bronchoconstriction (closing index) was computed as the percent reduction in FVC divided by the percent reduction in FEV 1 at maximal bronchoconstriction. Results: A total of 116 asthmatic patients (56 obese) underwent methacholine challenge. Spirometric lung function was inversely related to WC (P < 0.05), rather than BMI. Closing index increased significantly during bronchoconstriction in obese patients and was related to increasing BMI (P = 0.01), but not to WC. Sensitivity to airway closure and narrowing was not associated with BMI or WC. Conclusion: Although WC is associated with restrictive effects on baseline lung function, increased BMI, rather than WC, predisposes to airway closure during bronchoconstriction. These findings suggest that obesity predisposes to airway closure during bronchoconstriction through mechanisms other than simple mass loading.

Contemporary Concise Review 2019: Asthma

“…Interestingly, they found that waist circumference was closely related to restrictive spirometry changes, with reductions in FEV 1 and FVC, but was not related to the closing index. However, BMI was associated with an increased FVC . Using multivariate analysis, the closing index was related to BMI but not waist circumference.…”

“…Using this large cohort, they demonstrated that, with multivariate regression, both increasing age and obesity were associated with an increased closing index. To further define this mechanism, the investigators assessed the closing index and how this was related to body mass index (BMI) and waist circumference in a new study of 116 patients with asthma . Interestingly, they found that waist circumference was closely related to restrictive spirometry changes, with reductions in FEV 1 and FVC, but was not related to the closing index.…”

Obesity and the lungs: Not just a crush

“…The findings of Peters et al therefore add important understanding to an area that is poorly understood and will hopefully stimulate further research into mechanisms that explain the problems of obesity in asthma that continue to face clinicians in their everyday practice.…”

“…Compared with the knowledge of how obesity affects normal airways, less is known about how obesity affects asthmatic airways. Hence, the recently published study of asthmatic patients by Peters et al in Respirology , as well as previous publications from this group, is important in this regard. Their finding that obesity has minimal to no effect on sensitivity to bronchoconstriction is consistent with published data.…”

Fatty airways: a source of good and bad fats?

“…Obesity will cause extrathoracic restriction and is reported to promote airway hyperresponsiveness, most likely via increased airway closure [10]. This is related to obesity but not waist circumference [11], suggesting the effects might not simply be due to poor inspiratory effort due to diaphragmatic splinting but could be due to additional factors. Several studies have demonstrated that weight reduction by diet and exercise or bariatric surgery improve asthma outcomes, including symptoms, airway hyperresponsiveness and exacerbation frequency [12][13][14][15].…”