Isocapnic buffering phase: a useful indicator of exercise endurance in patients with coronary artery disease

Abstract

Objectives: The significance of the isocapnic buffering (IB) phase - the period between the first ventilatory threshold (1^st VT) and respiratory compensation point (RCP) - has not been adequately established in patients. This study aimed to determine the clinical significance of the IB phase in patients with coronary artery disease (CAD).

Methods: This retrospective study included data of sixty-two CAD patients after coronary artery bypass graft (CABG) or percutaneous coronary intervention (PCI) performed in a single medical center between 2010 - 2014. According to their physical conditions, the patients performed incremental cardiopulmonary exercise test (CPET) using a cycle ergometer by the ramp of 5-20 W/min. Correlations between the corrected IB phase duration and age, body mass index (BMI), left ventricular ejection fraction (LVEF), and CPET parameters were evaluated using Pearson correlation coefficients. Variables predicting peak oxygen consumption (VO₂) were evaluated using multiple regression.

Results: Peak VO₂ (p < 0.001), VO₂ at RCP (p < 0.001), ∆O₂/∆WR slope (p < 0.001), maximal partial pressure of end tidal CO₂ (PetCO₂) (p = 0.0012), VE/VCO₂ slope (p = 0.010), BMI (p = 0.012), and age (p = 0.017) were significantly correlated, whereas LVEF (p = 0.246) and VO₂ at 1^st VT (p = 0.179) were not significantly correlated with the corrected IB phase duration. In multiple regression analysis, the corrected IB phase duration, VO₂ at 1^st VT, and ∆O₂/∆WR slope were significantly associated with peak VO₂.

Conclusion: The findings indicate that the IB phase duration is a useful indicator of peripheral cardiopulmonary function and endurance performance in CAD patients. These findings could assist the exercise prescription of cardiac rehabilitation for patients with CAD.

Keywords: Isocapnic buffering phase; cardiopulmonary exercise test; cardiopulmonary function; coronary artery disease; endurance performance.