Influence of Low Peak Respiratory Exchange Ratio on Cardiac Rehabilitation in Patients With Coronary Artery Disease

Objective: To compare and analyze the effects of cardiac rehabilitation (CR) in two groups based on the peak respiratory exchange ratio (RER) 1.1 values using the exercise tolerance test (ETT) results, and to investigate the reasons for early termination of ETT.

Methods: Patients with acute coronary syndrome who participated in CR exercise training were selected and all subjects underwent 6 weeks of CR exercise training. ETT was performed on a treadmill using a Modified Bruce Protocol before and after CR exercise training. According to the result of the first ETT, the subjects were divided into two groups: those with an RER≥1.1 (n=33) and those with an RER<1.1 (n=22). We investigated the reasons for ETT termination and compared the effect of CR between the groups.

Results: The reasons for the early termination of the first ETT in the RER<1.1 group were subjective dyspnea, abnormal cardiovascular responses, leg fatigue and other problems. After a 6-week CR, the peak oxygen consumption (VO) and ETT time increased, and the rate of perceived exertion (RPE) and RPP (rate pressure product) at stage 3 decreased in both the RER<1.1 and RER≥1.1 groups.

Conclusion: CR exercise training improved exercise capacity, not only in the RER≥1.1 group, but also in the RER<1.1 group. This means that patients with a lower exercise tolerance could also benefit from the effects of CR. Thoughtful consideration to identify the direct and indirect causes for the early termination of ETT would be necessary to improve the efficiency of CR.