Overshoot of the Respiratory Exchange Ratio during Recovery from Maximal Exercise Testing in Kidney Transplant Recipients

Abstract

The overshoot of the respiratory exchange ratio (RER) during recovery from exercise has been found to be reduced in magnitude among patients with heart failure. The aim of this study is to investigate whether this phenomenon could also be present in patients with peripheral, and not cardiac, limitations to exercise such as kidney transplant recipients (KTRs). In this retrospective cross-sectional study, KTRs were evaluated with maximal cardiopulmonary exercise testing (CPET) assessing the RER overshoot parameters during recovery: the RER at peak exercise, the maximum RER value reached during recovery, the magnitude of the RER overshoot (RER mag = (RER max-peak RER)/peak RER%) and the linear slope of the RER increase after the end of exercise. A total of 57 KTRs were included in the study (16 females), all of them showing a significant RER overshoot (RER mag: 28.4 ± 12.7%). Moreover, the RER mag showed significant correlations with the fitness of patients (peak VO2: ρ = 0.57, p < 0.01) and cardiorespiratory efficiency (VE/VCO2 slope: r = −0.32, p < 0.05; oxygen uptake efficiency slope (OUES): r = 0.48, p < 0.01). Indeed, the RER mag was significantly different between the subgroups stratified by Weber’s fitness class or a ventilatory efficiency class. Our study is the first to investigate recovery of the RER in a population of KTRs, which correlates well with known prognostic CPET markers of cardiorespiratory fitness, determining the RER mag as the most meaningful RER overshoot parameter. Thus, the RER recovery might be included in CPET evaluations to further improve prognostic risk stratifications in KTRs and other chronic diseases.

Overshoot of the Respiratory Exchange Ratio during Recovery from Maximal Exercise Testing in Young Patients with Congenital Heart Disease

“…This shows how the overshoot phenomenon is closely related to maximal and submaximal aerobic capacity. Different from previous works, no correlation between RER mag and VE/VCO 2 slope was found [ 12 , 41 ]. This could be explained by the fact that the population in this study was young and might not have yet developed a relevant degree of ventilatory-perfusion mismatch.…”

“…To evaluate the potential clinical application of the RER overshoot, patients with CHD were grouped according to their ventilatory classes, which reflect the cardiorespiratory efficiency and a possible ventilation-perfusion mismatch during exercise. Patients with better ventilatory classes showed higher RER recovery overshoots compared with those belonging to worse ventilatory classes, similar to what was reported about kidney transplant recipients [ 41 ]. Furthermore, a vigorous RER overshoot seems to be an index of better cardiorespiratory performance and a better prognosis in patients with CHD.…”

“…This confirms previous studies on adults showing that gas exchange recovery after exercise testing is prolonged in patients with CHD, independently of the congenital heart lesion [ 17 ]. However, comparing our results with prior studies, RER mag of young patients with CHD (44.4 ± 14.8%) was higher compared to older patients with HF, kidney transplant recipients but also healthy older subjects (21.4 ± 12.4%, 28.4 ± 12.7% and 29.3 ± 10%, respectively) [ 12 , 41 ]. These findings suggest that age appears to be a crucial factor in determining this phenomenon in the recovery phase, as subjects with the established cardiac disease show higher values than healthy older subjects, even in CHD with the lowest cardiorespiratory fitness (RER mag in Fon group: 42.31 ± 13.10%).…”

The potential benefits of assessing post-cardiopulmonary exercise testing (CPET) in aging: a narrative review

“…Respiratory exchange ratio (RER), CO 2 produced/O 2 consumed, is an indirect measure of skeletal muscle capacity for oxidative phosphorylation [ 40 ]. Post-exercise RER can be used to measure the RER overshoot- defining the highest RER value during exercise (A) and recovery (B), and defining the percentage magnitude between these 2 points (A) and (B) [ 41 ]. Time to RER max was defined by duration between (A) and (B) [ 41 ].…”

“…Post-exercise RER can be used to measure the RER overshoot- defining the highest RER value during exercise (A) and recovery (B), and defining the percentage magnitude between these 2 points (A) and (B) [ 41 ]. Time to RER max was defined by duration between (A) and (B) [ 41 ]. Individuals with kidney transplant (51.4 ± 13.0 years old) showed significant RER overshoot, with a RER magnitude lower than healthy individuals; further, the RER magnitude was able to stratify according to fitness levels [ 41 ].…”