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Mechanical effects of obesity on airway responsiveness in otherwise healthy humans

¹Pneumologia-Fisiopatologia Respiratoria and ³Dietetica e Nutrizione Clinica, Azienda Ospedaliera S. Luigi, Orbassano (Torino); ²TBM Laboratory, Dipartimento di Bioingegneria, Politecnico di Milano, Milano, Italy; ⁴Department of Physiology and Biophysics, and Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, Minnesota; ⁵Fisiopatologia Respiratoria, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy; and ⁶Centro di Fisiopatologia Respiratoria e di Studio della Dispnea, Azienda Ospedaliera S. Croce e Carle, Cuneo, Italy

Submitted 28 January 2009 ; accepted in final form 16 June 2009

We investigated whether obesity is associated with airway hyperresponsiveness in otherwise healthy humans and, if so, whether this correlates with a restrictive lung function pattern or a decreased number of sighs at rest and/or during walking. Lung function was studied before and after inhaling methacholine (MCh) in 41 healthy subjects with body mass index ranging from 20 to 56. Breathing pattern was assessed during a 60-min rest period and a 30-min walk. The dose of MCh that produced a 50% decrease in the maximum expiratory flow measured in a body plethysmograph (PD₅₀MCh) was inversely correlated with body mass index (r² = 0.32, P < 0.001) and waist circumference (r² = 0.25, P < 0.001). Significant correlations with body mass index were also found with the maximum changes in respiratory resistance (r² = 0.19, P < 0.001) and reactance (r² = 0.40, P < 0.001) measured at 5 Hz. PD₅₀MCh was also positively correlated with functional residual capacity (r² = 0.56, P < 0.001) and total lung capacity (r² = 0.59, P < 0.001) in men, but not in women. Neither PD₅₀MCh nor body mass index correlated with number of sighs, average tidal volume, ventilation, or breathing frequency. In this study, airway hyperresponsiveness was significantly associated with obesity in otherwise healthy subjects. In obese men, but not in women, airway hyperresponsiveness was associated with the decreases in lung volumes.

methacholine response; body mass index; lung volumes; sighs; deep breath