The effect of time-of-day and chest physiotherapy on multiple breath washout measures in children with clinically stable cystic fibrosis

BACKGROUND: In this pilot study we investigated daytime variation of multiple breath nitrogen washout (N(2)MBW) measures in children with clinically stable cystic fibrosis. To our knowledge the effect of time-of-day on multiple breath washout measures in patients with cystic fibrosis has not previously been reported. Furthermore, we assessed the influence of chest physiotherapy on N(2)MBW measures. METHODS: Ten school children with cystic fibrosis performed N(2)MBW followed by spirometry and plethysmography in the morning and afternoon at three visits that were one month apart. Chest physiotherapy was performed immediately before the afternoon measurements at visit 2 and immediately before morning and afternoon measurements at visit 3. The influence of time-of-day and chest physiotherapy on the measures was evaluated using linear mixed models. RESULTS: There were adequate quality data from 8 children with median age (range) 9.6 (6.0; 15.1) years. Baseline lung clearance index (LCI) (range) was 9.0 (7.1; 13.0) and baseline FEV(1)% predicted was 97.5 (78.5; 117.9). No N(2)MBW measures were significantly influenced by time-of-day or chest physiotherapy. LCI (95% confidence interval) decreased non-significantly 0.05 (-0.32; 0.22) during the day and increased non-significantly 0.08 (-0.26; 0.42) after chest physiotherapy. All spirometric measures were unaffected by time-of-day and chest physiotherapy. For plethysmographic measures FRC(pleth) decreased significantly (p<0.01) 110 mL during the day, whereas a borderline significant (p = 0.046) decrease in ΔFRC(pleth-MBW) during the day and a borderline significant (p = 0.03) increase in TLC after CPT were observed. CONCLUSION: This study demonstrated that the time-of-day as well as chest physiotherapy performed immediately prior to N(2)MBW had no consistent or significant influence on N(2)MBW measures. However, we emphasize that further studies of the effect of both daytime variation and the effect of chest physiotherapy on multiple breath washout measures are warranted.