Background. Measurement of lung clearance index (LCI) and Functional Residual Capacity (FRC) with nitrogen multiple breath washout technique (N2MBW) is feasible in young infants, but use of pure oxygen may induce hypoventilation. The objective was to assess the frequency and impact of oxygen-induced hypoventilation on LCI in healthy infants.
Material and methods.LCI 2.5 and FRC were measured by N2MBW with pure oxygen using the Exhalyzer© and Spiroware© (Ecomedics) in healthy infants aged 6-10 weeks as part of the SEPAGES couple-child cohort. Up to 3 satisfactory measures were obtained during natural quiet sleep. Hypoventilation was defined by a decrease of at least 35 % of tidal volume for 5 or more consecutive breaths in the first minute after inhaling pure oxygen.
Results. Results are based on a subgroup of 83 infants (mean (sd) age = 7 (0.8) weeks, male = 51.8 %) who underwent 208 satisfactory measures (63%, 23% and 14% with 3, 2 and 1 measure(s), respectively). Hypoventilation occurred in 38 measures (18%), and 23 infants (28%) showed at least one measure with hypoventilation. Mean (sd) LCI2.5 was significantly lower in measures with hypoventilation than without hypoventilation (7.3 (1.2) vs 7.8 (1.3), p=0.01). FRC was similar in measures with and without hypoventilation (p=0.43).
Conclusion. Oxygen-induced hypoventilation in N2MBW was observed in at least one measure in about 1/4 of healthy infants, and was associated with lower LCI values. Further studies are needed to assess the robustness of the findings in larger samples and the risk factors for hypoventilation.