Slow and fast ventilated lung units in adult asthma assessed from N2 multiple-breath washouts (MBW)

Background: 3 He magnetic resonance imaging (MRI) studies in adults with bronchial asthma demonstrate the presence of markedly underventilated lung regions even when spirometry indicates normal airway function. Aim: To demonstrate the utilitiy of N 2 MBW, a simple and more affordable method, to quantify underventilated lung volumes in asthma. Subjects and Methods: 62 asthmatic subjects (33 males) aged 19-67 yrs (median 50 yrs) performed triplets of N 2 MBW using the Exhalyzer D (Eco Medics AG, Duernten, Switzerland) plus spirometry. Semi-log plots of exhaled N 2 volume per breath vs. breath number were used to calculate slow and fast emptying lung compartments and their specific ventilation. All ages (Stanojevic et al 2008) spirometry reference values and LCI reference equations from 510 healthy controls were used. Results: Median (range) slow compartment volume was 54% (36;77) of FRC (functional residual capacity). Slow and fast compartment specific ventilation were 7.4% (3.0; 27.9) and 40.2% (15.9; 105.0), respectively. Specific ventilation of slow compartment correlated inversely with LCI (R 2 =0.55; p 1 /FVC (R 2 =0.32; p Conclusion: Slow and fast compartments of FRC and their specific ventilation can be derived from simple N 2 MBW curves. The degree of underventilation of the slow compartment is a determinant of global ventilation inhomogeneity and correlates to the FEV 1 /FVC ratio.