Reproducibility of onset and recovery oxygen uptake kinetics in moderately impaired patients with chronic heart failure

Oxygen (O₂) kinetics reflect the ability to adapt to or recover from exercise that is indicative of daily life. In patients with chronic heart failure (CHF), parameters of O₂ kinetics have shown to be useful for clinical purposes like grading of functional impairment and assessment of prognosis. This study compared the goodness of fit and reproducibility of previously described methods to assess O₂ kinetics in these patients. Nineteen CHF patients, New York Heart Association class II–III, performed two constant-load tests on a cycle ergometer at 50% of the maximum workload. Time constants of O₂ onset- and recovery kinetics (τ) were calculated by mono-exponential modeling with four different sampling intervals (5 and 10 s, 5 and 8 breaths). The goodness of fit was expressed as the coefficient of determination (R ²). Onset kinetics were also evaluated by the mean response time (MRT). Considering O₂ onset kinetics, τ showed a significant inverse correlation with peak- \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{2} \) (R = −0.88, using 10 s sampling intervals). The limits of agreement of both τ and MRT, however, were not clinically acceptable. O₂ recovery kinetics yielded better reproducibility and goodness of fit. Using the most optimal sampling interval (5 breaths), a change of at least 13 s in τ is needed to exceed normal test-to-test variations. In conclusion, O₂ recovery kinetics are more reproducible for clinical purposes than O₂ onset kinetics in moderately impaired patients with CHF. It should be recognized that this observation cannot be assumed to be generalizable to more severely impaired CHF patients.