Clinical aspects of asthma

P124 REPRODUCIBILITY OF THE MULTIPLE BREATH NITROGEN WASHOUT TEST IN HEALTHY VOLUNTEERS AND SUBJECTS WITH MILD TO MODERATE ASTHMA

¹M. F. Biddiscombe, ²S. Verbanck, ³S. Meah, ³P. J. Barnes, ³O. S. Usmani. ¹Nuclear Medicine, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College London, London, UK, ²Respiratory Division, Academic Hospital, Vrije Universiteit, Brussels, Belgium, ³Airways Disease Section, Royal Brompton Hospital and National Heart and Lung Institute, Imperial College London, London, UK

Introduction The multiple breath nitrogen washout (MBNW) test is a non-invasive physiological tool that can be used to assess differences in ventilation heterogeneity arising in the proximal (conducting) from that in the distal (acinar) airway compartments. Abnormalities in the MBNW acinar (S_acin) and conductive (S_cond) airway indices have been observed and indicate significant ventilation heterogeneity in patients with asthma and chronic obstructive pulmonary disease (COPD).

Objectives To assess the same-day and day-to-day reproducibility of MBNW parameters (S_acin, S_cond) in 24 healthy volunteers (HV, mean forced expiratory volume in 1 s (FEV₁) 104%pred; age 22–59 years; males 12) and 12 patients with mild to moderate asthma (A, mean FEV₁ 92%pred; age 21–54 years; males 8).

Methods Each subject performed two MBNW runs (1 run = 3 MBNW tests) each day, on three separate days. Each MBNW test consisted of consecutive 1-litre oxygen inhalations until expired nitrogen was <2%.

Results Higher S_acin and S_cond (greater heterogeneity) values were detected in A vs HV subjects. Functional residual capacity (FRC) calculated from MBNW correlated with that measured using body plethysmography (r = 0.65; p<0.01). No correlation was observed between S_acin and S_cond and subject’s FEV₁, FVC or FEF_25–75 (p>0.10) for both groups. Day-to-day variability of S_acin and S_cond were greater than spirometric measures (table 1).

Conclusion S_acin and S_cond were significantly higher for asthmatic subjects compared with …