Congenital central hypoventilation syndrome (CCHS) is defined by central chemoreceptor dysfunction that produces a markedly reduced ventilatory drive to carbon dioxide. Although episodes of inadequate ventilation and hypercapnia during physical activity have been reported in CCHS, a quantitative evaluation of the ventilatory response to CO2 (VRCO2) during exercise had not been reported in the source article prior to this study. The authors aimed to measure VRCO2 during exercise and compare it with VRCO2 at rest to determine whether CO2-driven ventilatory control remains impaired under increased metabolic demand.
The study enrolled ten patients with genetically confirmed CCHS. Patients underwent a cardiopulmonary exercise test (CPET) using a stepwise incremental treadmill protocol with breath-by-breath respiratory gas analysis. The CPET protocol and termination criteria were prespecified: testing was stopped when end-tidal CO2 (EtCO2) increased by at least 2% (equivalent to 15.2 mmHg) from baseline.
VRCO2 during exercise was calculated as the change in minute volume (ΔMV) divided by the change in EtCO2, normalized to body weight (ΔMV/ΔEtCO2/body weight; reported as mL/min/mmHg/kg). Resting VRCO2 was measured using the CO2 rebreathing method. Data are presented as medians with interquartile ranges (IQR) in the article.
CPET employed a face mask with breath-by-breath gas analysis to record minute ventilation, oxygen uptake, CO2 output, EtCO2, and peripheral oxygen saturation (SpO2). A stepwise incremental treadmill protocol increased work rate until the predefined EtCO2 rise criterion was met. The article reports that written informed consent for image publication was obtained for figure materials. No additional procedural details beyond those summarized here were reported in the article.
Primary physiologic outcomes reported were VRCO2 during exercise and VRCO2 at rest. Secondary descriptive measures included exercise duration, changes in MV, EtCO2, and SpO2 during exercise. Comparisons between VRCO2 during exercise and at rest used nonparametric reporting (median and IQR); the reported p value for the comparison was 0.85, indicating no statistically significant difference between exercise and rest VRCO2 in this cohort. The article contrasts observed VRCO2 values with published values for healthy children.
Patient characteristics and exercise tolerance: The median age of participants was 13.5 years (IQR 12.3–15.5). Median exercise duration during CPET was 5 minutes 53 seconds (IQR 4 minutes 47 seconds to 6 minutes 56 seconds).
Ventilatory and gas exchange responses: Although minute volume increased during exercise, peripheral oxygen saturation (SpO2) decreased and EtCO2 increased, patterns consistent with relative hypoventilation during exercise in these patients. VRCO2 during exercise had a median value of 2.27 mL/min/mmHg/kg (IQR 1.61–3.16). Resting VRCO2 measured by CO2 rebreathing had a median of 1.56 (IQR 1.07–2.83). The difference between exercise and rest VRCO2 was not statistically significant (p = 0.85).
Comparison with healthy controls: The authors reported that VRCO2 in the CCHS patients was markedly lower than values reported for healthy children, which were cited as a median of 34.6 (IQR 29.3–42.8) in the source material.
Symptoms and safety: No patients reported dyspnea during testing, and no serious adverse events occurred during CPET in this cohort.
The study found that VRCO2 during exercise remains profoundly low in patients with CCHS and was not significantly different from VRCO2 at rest. These results indicate persistent impairment of CO2-driven ventilatory control even when metabolic demand increases during exercise. The dissociation between objective physiologic impairment and the absence of subjective dyspnea highlights the importance of objective testing—such as CPET and CO2 rebreathing measures—when assessing exercise tolerance and ventilatory sufficiency in patients with CCHS.
Clinically, these findings support cautious, individualized decision-making when recommending or supervising exercise for patients with CCHS and emphasize the need for objective physiological assessment rather than reliance on symptoms alone.
The authors declared no conflicts of interest. The article reports that no serious adverse events occurred during testing. Specific long-term safety outcomes, further protocol safety details, and broader generalizability considerations were not reported in the source article beyond what is summarized here.