Body mass impacts distal airway function

Obesity is a global health problem that adversely affects the respiratory system. We assessed the effects of body mass index (BMI) on distal airway function and airway inflammation in 34 healthy subjects using impulse oscillometry (IOS) and exhaled nitric oxide (eNO). Participants exhaled at various flows from 30 to 300 ml/s to determine total fraction of exhaled NO (FeNO-50ml/s) and alveolar and bronchial NO components. Nineteen subjects had normal BMI (18.50 - 24.99) whilst 15 subjects were overweight (BMI 25.00 - 29.99) or obese (BMI ≥ 30). All participants demonstrated normal spirometry values. However, airway resistance at 5Hz, 20Hz, and frequency dependence (FD) were significantly abnormally elevated in overweight/obese individuals, compared to subjects with normal BMI (median (Interquartile range (IQR)); 20Hz : 0.34 (0.30 - 0.37) vs. 0.30 (0.26 - 0.33) kPa/l/s; FD : 0.06 (0.04 - 0.11) vs. 0.03 (0.01 - 0.05) kPa/l/s; 5Hz : 0.41 (0.37 - 0.45) vs. 0.32 (0.30 - 0.37) kPa/l/s; all p‹0.05). Airway reactance at 20Hz was significantly lower in the overweight/obese group compared to the normal weight group ( 20 Hz : 0.07 (0.03 - 0.09) vs. 0.10 (0.07 - 0.13) kPa/l/s, p=0.01; 5Hz : -0.12 (-0.15 - -0.10) vs. -0.10 (-0.13 - -0.09) kPa/l/s, p=0.07). FeNO, alveolar and bronchial NO values did not differ between groups (p›0.05). We have demonstrated that being overweight has a significant influence on distal and central airway function as determined by IOS, which is not picked up by conventional spirometry. Obesity does not influence airway inflammation in healthy subjects. IOS is a quick and simple technique that can identify distal and central airway abnormalities even in the presence of normal spirometry in healthy overweight people.