Exercise training increases oxygen uptake efficiency slope in chronic heart failure

Background and aim The oxygen uptake efficiency slope (OUES) is a novel measure of cardiopulmonary reserve. OUES is measured during an exercise test, but it is independent of the maximally achieved exercise intensity. It has a higher prognostic value in chronic heart failure (CHF) than other exercise test-derived variables such as ${\stackrel{.}{V}}_{{\text{O}}_{2\text{peak}}}$ or $\stackrel{.}{V}E/{\stackrel{.}{V}}_{{\text{CO}}_2}$ slope. Exercise training improves ${\stackrel{.}{V}}_{{\text{O}}_{2\text{peak}}}$ and $\stackrel{.}{V}E/{\stackrel{.}{V}}_{{\text{CO}}_2}$ in CHF patients. We hypothesized that exercise training also improves OUES.

Methods and results We studied 34 New York Heart Association (NYHA) class II–III CHF patients who constituted an exercise training group T (N = 20; 19 men/1 woman; age 60 ± 9 years; left ventricular ejection fraction 34 ± 5%) and a control group C (N = 14; 13 men/one woman; age 63 ± 10 years; left ventricular ejection fraction 34 ± 7%). A symptom-limited exercise test was performed at baseline and repeated after 4 weeks (C) or after completion of the training program (T). Exercise training increased NYHA class from 2.6 to 2.0 (P [ 0.05), ${\stackrel{.}{V}}_{{\text{O}}_{2\text{peak}}}$ by 14% [P(TvsC)[0.01], and OUES by 19% [P(TvsC) [ 0.01]. Exercise training decreased $\stackrel{.}{V}E/{\stackrel{.}{V}}_{{\text{CO}}_2}$ by 14% [P(TvsC) [ 0.05].

Conclusion Exercise training improved NYHA class, ${\stackrel{.}{V}}_{{\text{O}}_{2\text{peak}}}$, $\stackrel{.}{V}E/{\stackrel{.}{V}}_{{\text{CO}}_2}$ and also OUES. This finding is of great potential interest as OUES is insensitive for peak load. Follow-up studies are needed to demonstrate whether OUES improvements induced by exercise training are associated with improved prognosis.