Assessment of the effects of physical training in patients with chronic heart failure: the utility of effort-independent exercise variables

Abstract

Traditionally, the effects of physical training in patients with chronic heart failure (CHF) are evaluated by changes in peak oxygen uptake (peak $\dot{V}{\text{O}}_{2}$). The assessment of peak $\dot{V}{\text{O}}_{2}$, however, is highly dependent on the patients’ motivation. The aim of the present study was to evaluate the clinical utility of effort-independent exercise variables for detecting training effects in CHF patients. In a prospective controlled trial, patients with stable CHF were allocated to an intervention group (N = 30), performing a 12-week combined cycle interval and muscle resistance training program, or a control group (N = 18) that was matched for age, gender, body composition and left ventricular ejection fraction. The following effort-independent exercise variables were evaluated: the ventilatory anaerobic threshold (VAT), oxygen uptake efficiency slope (OUES), the $\dot{V}_{\text{E}} /\dot{V}{\text{CO}}_{ 2}$ slope and the time constant of $\dot{V}{\text{O}}_{2}$ kinetics during recovery from submaximal constant-load exercise (τ-rec). In addition to post-training increases in peak $\dot{V}{\text{O}}_{2}$ and peak $\dot{V}_{\text{E}} ,$, the intervention group showed significant within and between-group improvements in VAT, OUES and τ-rec. There were no significant differences between relative improvements of the effort-independent exercise variables in the intervention group. In contrast with VAT, which could not be determined in 9% of the patients, OUES and τ-rec were determined successfully in all patients. Therefore, we conclude that OUES and τ-rec are useful in clinical practice for the assessment of training effects in CHF patients, especially in cases of poor subject effort during symptom-limited exercise testing or when patients are unable to reach a maximal exercise level.