Isocapnic buffering period: From physiology to clinics

Background: During cardiopulmonary exercise test, the isocapnic buffering period ranges between anaerobic threshold (AT) and respiratory compensation point (RCP). We investigated whether oxygen uptake (VO 2 ) increase during the isocapnic buffering period (ΔVO 2 AT-RCP) is related to heart failure severity and prognosis. Methods: We retrospectively analysed reduced ejection fraction heart failure patients who attained RCP at cardiopulmonary exercise test. The study endpoint was the composite of cardiovascular mortality and urgent heart transplantation/left ventricular assist device implantation. Hazard ratio was assessed to identify the increase of risk associated with ΔVO 2 AT-RCP (below and above the median of ΔVO 2 AT-RCP). Results: AT and RCP were both identified in 782 (39.2%) out of 1995 reduced ejection fraction heart failure cases. Left ventricular ejection fraction and peak VO 2 were 33 ± 9% and 16.5 ± 4.5 mL/kg per min (61 ± 16% of predicted value), suggesting moderate heart failure. At five years, endpoint did not vary between patients below and above the median ΔVO 2 AT-RCP (3.85 mL/min per kg (25–75th interquartile range = 2.69–5.46)). ΔVO 2 AT-RCP correlated with several parameters associated to heart failure prognosis, such as peak VO 2 , VE/VCO 2 slope, brain natriuretic peptide and left ventricular ejection fraction. The ΔVO 2 AT-RCP value was associated with prognosis at univariate but not at multivariable analysis, where only VE/VCO 2 slope endured. Conclusion: ΔVO 2 AT-RCP correlates with several parameters linked to heart failure severity. Isocapnic buffering period stratifies heart failure patients, but not more than other prognostic indices.