Relationship between exercise oxygen kinetics and exercise performance in heart failure

Background Dyspnea and fatigue are typical exercise limitation symptoms in heart failure (HF). In HF, peak oxygen uptake (peak VO2) is decreased as well as its incremental increase and ventilatory threshold occurs early. A relevant integration to the study of the O2 kinetics in HF is provided by the O2 decay in the recovery phase. Aim We aimed at investigating the relationship between the O2recovery kinetics measured as the VO2 decay "τ" from peak exercise and gas exchange performance, peak VO2 and cardiac output (CO). Methods and results We enrolled a population of 51 HF - 28 HFpEF and 23 HFrEF - and a control population. All subjects underwent a symptom-limited combined cardiopulmonary exercise testing imaging (echoCPET). We measured τ using the formula VO2 (t)= VO2 (b) + A [1 - e -(t- TD) τ ], which describes O2credit in the recovery phase from maximal exercise (Figure 1). HFpEF patients (mean age 74.5 ± 7.5, 60% female) and HFrEF patients (mean age 64.6 ± 11.4, 21% female) showed a lower peak VO2 than controls (14.1 ± 3.2 ml/min/kg vs 16.9 ± 4.6 ml/min/kg vs 22,39 ± 5,31 ml/min/kg, respectively). HF exhibited a higher value of τ compared to the control population (τ mean= 151.3 in HFpEF; 188.2 in HFrEF; 90 in controls). τ value was strongly correlated with impairment of exercise performance, especially peak VO2 and CO, in both HF phenotypes (r=0.57 p<0.001; r=0.64 p<0.001; r=0.55 p<0.001, Figure 2). Conclusions Recovery O2 consumption by τ value represents a simple and effective parameter to be added to the constellation of gas exchange variables indicative of organ systems impaired performance and circulatory defects. Findings prospect a role for t in the evaluation of effectiveness of therapeutic interventions.