Introduction: Capillary partial pressure of O2 (PcapO₂) was found to decrease with age in children with primary ciliary dyskinesia (PCD) while PcapCO₂ remained steady.Objectives: To further explore the relationship between PcapO₂, nasal Nitric Oxide (nNO) output and lung function (LF) in children with PCD.Patients and methods: Retrospective monocentric study in children referred to our national paediatric reference center for rare lung diseases for PCD diagnostic work-up, and in whom ear lobe capillary blood gas was available along with nNO and/or LF measurements.Results: 30 PCD children were included (18 girls, median age 11.5 (0.7 to 18.2) years). Median PcapO₂ was -1.9 (-5.2 to 2.2) z-score, median nNO in 27 children was 61 (20.3 to 697) ppb and median FEV₁ in 24 children was -2 (-4.7 to 2.18) z-score.In univariate analysis, there was a significant relationship between PcapO₂ and nNO, age, and LF indices (see table).

Correlation between PcapO2 and nNO / LF tests
PcapO2rho= 0.44 p= 0.02rho= 0.69 p< 0.001rho= 0.49 p= 0.001rho= 0.48 p= 0.002rho= 0.68 p< 0.001rho= 0.75 p< 0.001rho= 0.56 p= 0.02
. In multivariate analysis, there was a significant relationship between PcapO2 and nNO (p=0.02), and FEF75% (p<0.001).Conclusion: In the study children, low PcapO2 was correlated with decrease nNO output and one LF indice. This could explain the early occurrence of hypoxemia in the course of PCD disease.