The effect of low lung volume on airway function in obesity.

INTRODUCTION

Obesity is associated with reduced operating lung volume. We hypothesized that obesity induces airway dysfunction independent of reduced FRC.

METHODS

18 obese (BMI: 41.3 ± 6.8) and 17 non-obese subjects (BMI: 24.8 ± 2.3 kg/m(2)) had measurements of conductance (Grs) and reactance (Xrs) by forced oscillation technique, ventilation heterogeneity (lung clearance index (LCI), Scond, Sacin) by multiple breath nitrogen washout and closing capacity (CC) by single breath nitrogen washout.

RESULTS

Obese had higher LCI and Sacin and lower Grs and Xrs. After adjustment for FRC, Grs (r=-0.52, p=0.001), and Sacin (r=0.47, p=0.004) still correlated with BMI. Closing capacity (as % predicted TLC) was not increased but was closer to FRC in the obese (CC/FRC: 95.0 ± 21.7% vs 71.7 ± 19.2%, p<0.001). Xrs and LCI correlated with CC/FRC.

CONCLUSIONS

In obesity, there are abnormalities in airway function that are independent of reduced FRC. Airway closure is not increased but CC occurs close to FRC, affecting Xrs and LCI.