Impaired ventilation during 6-min walk test in congenital central hypoventilation syndrome

Background: Patients with congenital central hypoventilation syndrome (CCHS) can develop hypoxemia and hypercapnia during exercise. However, there is limited literature on cardiorespiratory responses during submaximal exercise and their correlation with paired-like homeobox 2B (PHOX2B) genotype.

Objectives: To assess oxygen saturation (SpO₂ ), end-tidal carbon dioxide (ETCO₂ ), heart rate (HR), and 6-min walk distance (6MWD) during a 6-min walk test (6MWT) in CCHS subjects and to correlate them with PHOX2B genotypes and assisted ventilation (AV) via tracheostomy.

Methods: In this cross-sectional study, subjects with CCHS performed 6MWT with continuous pulse oximetry, HR, and capnography recorded before and during the 6MWT. Medical records were reviewed for PHOX2B genotype and phenotype data. Patients were categorized based on PHOX2B genotype and AV via tracheostomy.

Results: Fifteen subjects aged 10.5 (interquartile range 7.9-16.2) years completed the 6MWT. Nine subjects used AV via tracheostomy. Seven (47%) subjects developed hypoxemia (SpO₂ ≤ 90%, n = 7) and hypoventilation (ETCO₂ ≥ 50 mmHg, n = 3) during the 6MWT. There was a significant decline from baseline SpO₂ , increase from baseline ETCO₂ , and increase in HR during the 6MWT (all p < 0.05). Subjects had decreased median percent predicted 6MWD (59.7% [50.6%-62.5%]). Nadir SpO₂ (p = 0.029) and peak ETCO₂ (p = 0.046) differed significantly between PHOX2B genotype groups but 6MWD did not (p = 0.8).

Conclusion: Despite normal oxygenation and ventilation at rest and during sleep on AV, patients with CCHS can develop hypoxemia and hypercapnia during submaximal exercise. Our study highlights the importance of assessing ventilatory responses during submaximal exercise in patients with CCHS regardless of their PHOX2B genotype.