Purpose: The analysis of oxygen (O(2)) uptake on-kinetics during steady-rate is gaining interest in the heart failure (HF) population. The rate change in O(2) at the initiation of exercise can be assessed via nonlinear regression time constant (TC) or an algebraic equation (mean response time [MRT]). These calculations are presumed to be interchangeable, but research supporting this claim is limited. This investigation compares and contrasts two of the more commonly used O(2) uptake on-kinetic calculations.
Method: Twenty-eight subjects diagnosed with compensated HF and 19 age, sex, and activity-matched controls underwent a symptom-limited exercise test and a steady-rate exercise session (6 min). Peak O(2) uptake, O(2) uptake at ventilatory threshold, the O(2) uptake TC (TC), and the O(2) uptake mean response time (MRT) were calculated for each subject.
Results: O(2) uptake on-kinetics was significantly faster for the control group ( < 0.05) regardless of calculation method. There was a significant difference between the O(2) uptake TC and MRT for the HF group. All O(2) uptake on-kinetic calculations were significantly correlated with aerobic capacity.
Conclusions: O(2) uptake TC and MRT values may not be interchangeable in the HF population. All O(2) uptake on-kinetic calculations did produce a significant difference between experimental and control groups and correlated with indicators of aerobic capacity. The 10-s O(2) uptake on-kinetic calculations may be preferable secondary to expired gas fluctuations associated with breath-by-breath measures. Further work is, however, needed to determine which averaged O(2) uptake on-kinetic expression is optimal given the significant difference between TC and MRT. A mechanism for this difference may be the oscillatory ventilatory expired gas pattern demonstrated by some patients with HF.