Overshoot Of The Respiratory Exchange Ratio During Recovery From Maximal Exercise In Kidney Transplant Recipients

Abstract

PURPOSE: The overshoot of the respiratory exchange ratio (RER) during recovery from maximal cardiopulmonary exercise testing (CPET) has been found reduced in magnitude among patients with heart failure, possibly due to the slow recovery kinetics of VO2. To investigate whether this phenomenon could be present also in patients with peripheral limitations to exercise, a population of kidney transplant recipients (KTRs) was specifically studied, since these patients may present peripheral alterations at the muscular and microvascular level. METHODS: RER was retrospectively evaluated during recovery after maximal exercise (peak RER > 1.1) in KTRs without history of systolic dysfunction that underwent CPET for clinical purposes. Variables assessed were the maximum RER during recovery (RER-max), the RER overshoot magnitude (RER-OM: (RER-max - peak RER) / peak RER %) and the time from peak RER to RER-max. Patients signed informed consent. RESULTS: 57 KTRs were included in the study (28% females). The median value of peak RER was 1.2 (IQR 0.1). Mean RER-max and RER-OM were 1.6 ± 0.2 and 28.4 ± 12.7%, respectively. The time to reach RER-max was on average 131.4 ± 42.8 s. RER-OM showed significant correlations with peak VO2 (ρ =0.57; P<0.01), VO2 at the anaerobic threshold (r=0.44; P<0.01), VE/VCO2 slope (r=-0.32; P<0.05) and oxygen uptake efficiency slope (r=0.48; P<0.01). RER-max showed comparable correlations with these parameters, however, conversely to RER-OM, it was conditioned by peak RER (ρ=0.50; P<0.01). Finally, RER-OM was found significantly different among sub-populations of KTRs when stratified by patients’ aerobic capacity (Weber class A vs. B+C: 31.1 ± 12.1% vs. 18.6 ± 9.9%; P<0.01) or ventilatory efficiency (Ventilatory class I vs. II: 30.9 ± 13.3% vs. 23.2 ± 9.6%; P=0.03). CONCLUSIONS: This is the first study in KTRs investigating the recovery of RER, which seems to be affected by patients’ cardiorespiratory fitness. The present data showed that the RER-OM values of this population are similar to normal subjects’ values reported in literature. Moreover, RER-OM appears as a valuable parameter to assess the recovery of RER, being independent from peak RER and directly correlated to other prognostic CPET parameters.