Increased wheeze and asthma diagnosis in obesity may be due to reduced lung volume with subsequent airway narrowing.Asthma (wheeze and airway hyperresponsiveness), functional residual capacity (FRC) and airway conductance (Gaw) were measured in 276 randomly selected subjects aged 28-30 yrs. Data were initially adjusted for smoking and asthma before examining relationships between weight and FRC (after adjustment for height), and between body mass index (BMI5 weight?height -2 ) and Gaw (after adjustment for FRC) by multiple linear regression, separately for females and males.For males and females, BMI (¡95% confidence interval) was 27. , and FRC was 85.3¡3.4 and 84.0¡2.9% of predicted. Weight correlated independently with FRC in males and females. BMI correlated independently and inversely with Gaw in males, but only weakly in females.In conclusion, obesity is associated with reduced lung volume, which is linked with airway narrowing. However, in males, airway narrowing is greater than that due to reduced lung volume alone. The mechanisms causing airway narrowing and sex differences in obesity are unknown.

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Airway distensibility measured by forced oscillation technique is reduced in subjects with asthma compared with subjects without asthma, is not related to lung elastic recoil, and is unchanged by bronchodilator administration. Airway wall remodeling remains the most likely cause of reduced airway distensibility in asthma.