The effect of body weight on distal airway function and airway inflammation

Background/Objectives: Obesity is a global health problem that adversely influences the respiratory system. We assessed the effects of body mass index (BMI) on distal airway function and airway inflammation. Subjects/Methods: Impulse oscillometry (IOS) as a measure of distal airway function, together with spirometry, were assessed in adults with a range of different BMIs. Airway inflammation was assessed with the fraction of exhaled nitric oxide (FeNO) and participants exhaled at various exhalation flows to determine alveolar and bronchial NO. Results: In total 34 subjects were enrolled in the study; 19 subjects had a normal BMI (18.50-24.99), whilst 15 subjects were overweight (BMI 25.00-29.99), or obese (BMI >= 30). All subjects had normal spirometry. However, IOS measures of airway resistance (R) at 5 Hz, 20 Hz and frequency dependence (R5-20) were elevated in overweight/obese individuals, compared to subjects with a normal BMI (median (interquartile range)); 5 Hz: 0.41 (0.37, 0.45) vs. 0.32 (0.30, 0.37) kPa/l/s; 20 Hz: 0.34 (0.30, 0.37) vs. 0.30 (0.26, 0.33) kPa/l/s; R5-20: 0.06 (0.04, 0.11) vs. 0.03 (0.01, 0.05) kPa/l/s; p <0.05), whereas airway reactance at 20 Hz was decreased in overweight/obese individuals (20 Hz: 0.07 (0.03, 0.09) vs. 0.10 (0.07, 0.13) kPa/l/s, p = 0.009; 5Hz: -0.12 (-0.15, -0.10) vs. -0.10 (-0.13, -0.09) kPa/l/s, p = 0.07). In contrast, within-breath IOS measures (a sign of expiratory flow limitation) and FeNO inflammatory measures, did not differ between groups (p > 0.05). Conclusions: Being overweight has significant effects on distal and central airway function as determined by IOS, which is not detected by spirometry. Obesity does not influence airway inflammation as measured by FeNO. IOS is a reliable technique to identify airway abnormalities in the presence of normal spirometry in overweight people.