Simulated obesity-related changes in lung volume increases airway responsiveness in lean, nonasthmatic subjects

Study objective: To determine if obesity-related changes in lung volume might contribute to airway reactivity, we investigated the effects of simulated mild obesity-related lung volume reductions on airway responsiveness in lean, nonasthmatic subjects. Participants and methods: We simulated the lung volume reductions of class 1 obesity in eight lean, nonasthmatic subjects by externally mass loading the chest wall and abdomen, and shifting blood volume into the lung with lower limb compression (LLC). Airway responsiveness was assessed by measuring FEV₁ before and after methacholine challenge tests (1, 2.5, 5, 10, and 25 mg/mL) with the following: (1) no intervention (control); (2) external chest loading (CL); (3) LLC; and (4) CL and LLC (COMB) on separate days. Lung function was measured before and after CL, LLC, and COMB were applied. Results: The application of CL, LLC, and COMB decreased expiratory reserve volume, functional residual capacity, and total lung capacity compared with baseline. FVC and FEV₁ decreased significantly with CL and COMB, while FEV₁/FVC did not change compared to baseline. The maximal response to the methacholine challenge increased with CL, LLC, and COMB, with a mean maximal fall of FEV₁ of 9%, 11%, and 18%, respectively, compared to a 6% fall with control. Conclusions: We conclude that decreases in lung volume increase airway responsiveness and may account for the increased propensity for increased airway responsiveness in the obese.