The Single-Breath Diffusing Capacity of CO and NO in Healthy Children of European Descent

<div><p>Rationale</p><p>The diffusing capacity (D_L) of the lung can be divided into two components: the diffusing capacity of the alveolar membrane (Dm) and the pulmonary capillary volume (Vc). D_L is traditionally measured using a single-breath method, involving inhalation of carbon monoxide, and a breath hold of 8–10 seconds (D_L,CO). This method does not easily allow calculation of Dm and Vc. An alternative single-breath method (D_L,CO,NO), involving simultaneous inhalation of carbon monoxide and nitric oxide, and traditionally a shorter breath hold, allows calculation of Dm and Vc and the D_L,NO/D_L,CO ratio in a single respiratory maneuver. The clinical utility of Dm, Vc, and D_L,NO/D_L,CO in the pediatric age range is currently unknown but also restricted by lack of reference values.</p><p>Objectives</p><p>The aim of this study was to establish reference ranges for the outcomes of D_L,CO,NO with a 5 second breath hold, including the calculated outcomes Dm, Vc, and the D_L,NO/D_L,CO ratio, as well as to establish reference values for the outcomes of the traditional D_L,CO method, with a 10 second breath hold in children.</p><p>Methods</p><p>D_L,CO,NO and D_L,CO were measured in healthy children, of European descent, aged 5–17 years using a Jaeger Masterscreen PFT. The data were analyzed using the Generalized Additive Models for Location Scale and Shape (GAMLSS) statistical method.</p><p>Measurements and Main Results</p><p>A total of 326 children were eligible for diffusing capacity measurements, resulting in 312 measurements of D_L,CO,NO and 297 of D_L,CO, respectively. Reference equations were established for the outcomes of D_L,CO,NO and D_L,CO, including the calculated values: Vc, Dm, and the D_L,NO/D_L,CO ratio.</p><p>Conclusion</p><p>These reference values are based on the largest sample of children to date and may provide a basis for future studies of their clinical utility in differentiating between alterations in the pulmonary circulation and changes in the alveolar membrane in pediatric patients.</p>