ABSTRACT
Background and objective: Cross-sectional and longer-term studies have demonstrated abnormal yet stable multiple-breath inert gas washout (MBW) indices in patients with primary ciliary dyskinesia (PCD). This study aimed to assess the intermediate term evolution and the between-occasion variability of MBW indices in PCD over 1 year. Methods: Children and young adults with a confirmed diagnosis of PCD were included in this single-centre, prospective, observational, longitudinal study. Over 1 year, nitrogen (N2) MBW and spirometry were performed at three occasions during ordinary scheduled outpatient visits. Trends and variability in lung clearance index (LCI), moment ratios, normalized N2 concentration at six lung volume turnovers, and regional ventilation inhomogeneity indices of the conducting and intra-acinar airways (Scond*VT and Sacin*VT) were analysed using linear mixed models. Results: Forty-two patients, aged 6-29 years (median: 15.4), performed 116 N2 MBW test occasions and 96.6% were technically acceptable. A minimal, although significant, increase in LCI over 1 year (mean: 0.51 units, 95% CI: 0.12-0.91, p = 0.01) was found; while, all other N2 MBW indices and FEV1 remained unchanged. A moderate correlation was observed between LCI and FEV1 (r = -0.47, p = 0.0001). The limits of agreement between tests 1 year apart were for LCI: -1.96 to 2.98; Scond*VT: ± 0.039; Sacin*VT: -0.108 to 0.128. Conclusions: Children and young adults with PCD managed at a specialist centre showed slightly, but significant, increasing LCI and otherwise unchanged ventilation inhomogeneity indices and dynamic volumes over the intermediate term of 1 year. Estimates of the variability of N2 MBW indices may inform sample size calculations of future randomized controlled trials.
ABSTRACT
BACKGROUND: Commercial aircraft are pressurised to ~2438 m (8000 ft) above sea level that equates breathing 15% oxygen at sea level. A preflight hypoxic challenge test (HCT) is therefore recommended for children with cystic fibrosis or other chronic lung diseases and inflight oxygen is advised if pulse oximetric saturation (SpO2) decreases <90%. OBJECTIVE: Study responses to a modified HCT, encompassing various body positions and light physical activity, reflecting relevant activities of children during flight, with a view to challenge the evidence of the current cut-off. METHODS: Oxygenation, heart rate and ventilation were observed in 34 healthy schoolchildren (17 boys) undergoing a modified HCT, alternating between breathing room air and 15% oxygen in nitrogen while seated, supine, standing and walking at 3 km/h and 5 km/h. RESULTS: Nadir SpO2 <90%, median (range), occurred in 9 subjects sitting, 89% (78-89%); 6 supine, 88.5% (87-89%); 9 standing, 89% (85-89%); 23 walking 3 km/h, 87% (74-89%); and 21 walking 5 km/h, 86% (74-89%). Total time <90% for these subjects in seconds was 20 (10-80) sitting, 30 (10-190) supine, 50 (10-150) standing, 80 (10-260) walking 3 km/h and 125 (10-300) walking 5 km/h. Light exercise in general led to lower SpO2: 91% (77-96%), p<0.0001. CONCLUSIONS: A modified HCT led to moments of desaturation below 90% in various body positions at rest and during light physical activity in healthy schoolchildren. It is questionable whether the international recommended cut-off of 90% for children with chronic lung disease reflects clinical oxygen dependence during flights.
