Analysis of the overshoot of the respiratory exchange ratio during recovery from maximal exercise testing in patients with heart failure with reduced ejection fraction

Type of funding sources: None.

Transient increases (overshoot) in respiratory gas analysis parameters have been observed during recovery after maximal cardiopulmonary exercise testing (CPET), but their clinical significance is not clearly understood.(1) Respiratory exchange ratio (RER) at peak exercise (RER peak) is an objective index to evaluate exercise effort.(2) Moreover, overshoot phenomenon of the RER is commonly observed during recovery from CPET.(3) On the other hand, the overshoot of some CPET parameters during recovery has been found reduced in magnitude in patients with heart failure with reduced ejection fraction (HFrEF).(4)

We aimed to examine the clinical significance of RER behaviour after a maximal effort and to understand if this could help in the classification of specific subpopulations of patients.

In this cross-sectional study patients with HFrEF who underwent functional evaluation with CPET between 2017 and 2020 were included. A maximal CPET with at least two minute of recorded recovery was performed and always RER achieved at peak of exercise was higher than 1.10. RER behaviour during recovery has been evaluated, assessing its maximal value (RER max), the magnitude of the RER overshoot (RER mag), the time to reach RER max during recovery and the linear slope of increase of the RER from peak exercise to RER max (RER slope). Additionally, subgroup analyses were performed.

80 patients with HFrEF were included. Figure 1 shows an example of analyzed RER overshoot parameters. Principal clinical characteristics, CPET parameters and recovery metrics are shown in Table I. Significant correlations between RER recovery parameters and prognostically relevant CPET indices of cardiorespiratory fitness and efficiency were found, especially between RER mag and VO2peak (r=0.333; p=0.03), and RER mag and VE/VCO2slope (r= - 0.494; p<0.01). At multiple linear regression, VE/VCO2slope was the only determinant of RER mag. Patients in a more severe disease state (Ventilatory class III/IV and Weber’s classes C/D) present RER overshoot parameters significantly reduced compared with those in a light/moderate disease state (Ventilatory class I/II and Weber’s classes A/B), (all p=0.01).

The overshoots phenomena of RER during recovery from maximal exercise were associated with patients’ cardiopulmonary function, and their magnitudes were less prominent in HFrEF patients with a lower cardiorespiratory efficiency. Thus, the evaluation of the overshoot during recovery from CPET might represent an interesting clinical and prognostic tool in patients with HFrEF.