In patients with heart failure, enhanced ventilatory response to exercise is associated with severe obstructive sleep apnea

Study Objectives: Patients with congestive heart failure (CHF) frequently exhibit an elevated ratio of minute ventilation over CO2 output (VE/VCO2 slope) while undergoing exercise tests. One of the factors contributing to this elevated slope is an increased chemosensitivity to CO2 in that this slope significantly correlates with the slope of the ventilatory response to CO2 rebreathing at rest. A previous study in patients with CHF and central sleep apnea showed that the highest VE/VCO(2 )slope during exercise was associated with the most severe central sleep apnea. In the current study, we tested the hypothesis that in patients with CHF and obstructive sleep apnea (OSA), the highest VE/VCO2 slope is also associated with the most severe OSA. If the hypothesis is correct, then it implies that in CHF, augmented instability in the negative feedback system controlling breathing predisposes to both OSA and central sleep apnea. Methods: This preliminary study involved 70 patients with stable CHF and a spectrum of OSA severity who underwent full-night polysomnography, echocardiography, and cardiopulmonary exercise testing. Peak oxygen consumption and the VE/VCO2 slope were calculated. Results: There was significant positive correlation between the apnea-hypopnea index and the VE/VCO2 slope (r= .359; P= .002). In the regression model, involving the relevant variables of age, body mass index, sex, VE/VCO2 slope, peak oxygen consumption, and left ventricular ejection fraction, the apnea-hypopnea index retained significance with VE/VCO2. Conclusions: In patients with CHF, the VE/VCO2 slope obtained during exercise correlates significantly to the severity of OSA, suggesting that an elevated CO 2 response should increase suspicion for the presence of severe OSA, a treatable disorder that is potentially associated with excess mortality.