Phase Difference between End-Tidal CO₂ and Ventilation in Heart Failure with Oscillatory Breathing

Introduction: Oscillatory breathing (OB) observed during cardiopulmonary exercise testing (CPX) is a critical phenomenon, especially in patients with heart failure. Patients with cardiovascular diseases with OB usually present with cyclic changes not only in ventilation (VE) but also in oxygen uptake (VO2), carbon dioxide output (VCO2), end-tidal partial pressure of carbon dioxide (PETCO₂, reflecting dynamic changes in arterial PCO₂), and other respiratory gas variables. We aimed to evaluate whether the phase difference between the respiratory gas variables obtained from CPX is correlated with cardiopulmonary function. Methods: From a retrospective analysis of 1,740 patients with cardiovascular diseases who underwent CPX, 42 patients (65±13 years) with clear OB were selected. Oscillatory changes were observed in VE, VO2, VCO2, PETCO2, and end-tidal oxygen tension (PETO2) in all patients. PETCO2 and PETO2 oscillated almost simultaneously, although their peak and nadir were reversed. Oscillatory changes in PETCO2 and PETO2 preceded those in the other cardiopulmonary variables. After the peak of oscillating PETCO2, the oscillations of VO2, VCO2, and VE followed this order. Results: The phase difference between PETCO2 and VE was significantly and positively correlated with the VE–VCO2 slope, PETCO2 at rest, and PETCO2 at peak (r=0.414, p=0.006; r=–0.453, p=0.003; and r=–0.424, p=0.005, respectively). Conclusion: The phase difference between PETCO₂ and VE is associated with the severity of heart failure and suggests that oscillatory breathing may be partly related to impaired PaCO₂ regulation in patients with cardiovascular diseases.