Sleep-Disordered Breathing with Nighttime Hypocapnia Relates to Daytime Enhanced Ventilatory Response to Exercise in Patients with Heart Disease

Abstract

Background: Sleep-disordered breathing (SDB) induces nighttime disturbance of arterial gases, such as carbon dioxide. However, it is still unclear whether nighttime SDB-related gas abnormality is related to respiratory dysregulation in daytime. Therefore, we examined the relationship between the arterial partial pressure of carbon dioxide (PaCO₂) at nighttime and the respiratory response to exercise in daytime.
Methods: Eighteen men (age, mean ± SD; 55 ± 11 years) with heart disease underwent multichannel respiratory monitoring through the night with transdermal measurement of PaCO₂ (PtcCO₂) reflecting PaCO₂ and a cardiopulmonary exercise test in daytime. The ventilatory equivalent (VE)/carbon dioxide production (VCO₂) slope as an index of ventilatory response to exercise and peak oxygen consumption (VO₂) were obtained with a cardiopulmonary exercise test.
Results: Of the 18 patients, 10 patients had obstructive SDB, 5 had central SDB, and 3 patients did not have SDB. The mean apnea-hypopnea index was 21 ± 17. Minimum nighttime saturation of O₂ was positively correlated with peak VO₂, but not with VE/VCO₂. Nighttime PtcCO₂ was not correlated with peak VO₂ but was negatively correlated with the VE/VCO₂ slope of the daytime cardiopulmonary exercise test (r=-0.53).
Conclusion: Nighttime lowering of PaCO₂ in SDB is related to an abnormal ventilatory response to exercise testing in the daytime. This finding suggests that nighttime hyperventilation in SDB alters both nighttime and daytime pathophysiological conditions in patients with heart disease.