End-tidal CO₂ pressure and cardiac performance during exercise in heart failure

Introduction: In patients with, heart failure (HF), end-tidal CO ₂ pressure (PetCO₂) is related to ventricular function at rest and has been shown to predict prognosis. However, little is known about the association between ventricular performance and PeCO₂ responses to exercise. Methods: Forty-eight patients with HF and 13 normal subjects underwent cardiopulmonary exercise testing (CPX), while cardiac output and other hemodynamic measurements at rest and during exercise were obtained using a novel, noninvasive, bioreactance device based on assessment of relative phase shifts of electric currents injected across the thorax, heart rate, and ventricular ejection time. CPX responses and indices of cardiac performance were compared between normal subjects and HF patients achieving above and below a PeCO₂ of 36 mm Hg at the ventilatory threshold (PeCO ₂2@VT). Results: HF patients with an abnormal PetCO₂@VT (<36 mm Hg) had a lower exercise capacity, a lower VO₂@VT, a higher V_E/VCO₂ slope, and lower oxygen uptake efficiency slope (OUES) values compared with normal subjects and patients achieving a normal PeCO₂(SjVT. Patients with reduced PetCO₂@VT had lower peak cardiac output responses to exercise (20.0 ± 10, 17.8 ± 6, and 13.7 ± 7 Lmin^-1 for normal subjects and HF patients with normal and abnormal PeCO₂ responses to exercise, respectively, P = 0.04). PetCO₂@VT was inversely related to the V _E/VCO₂ slope (r = -0.78, P < 0.001) and directly related to the OUES (r = 0.55, P < 0.001). Conclusion: Reduced PetCO ₂ reflects impairments in the functional, ventilatory, and cardiac performance response to exercise in patients with HF. PeCO₂ can supplement other clinical and CPX indices in the functional and prognostic evaluation of patients with HF.