Dissociating the Attainment of Maximal Oxygen Uptake from Symptom Limitation During Exercise in Heart Failure

Abstract

Mortality in heart failure (HF) is especially high in patients with peak O2 uptake (VO2) ≤14 mL.kg-1.min-1, hence this value is a widely used cut-off criterion for cardiac transplantation (Mehra et al. J Heart Lung Transplant 25:1024-, 2006). However, exercise testing in HF is symptom limited and cessation may occur before reaching the physiological limit to O2 uptake (VO2max). Therefore a respiratory exchange ratio (RER) >1.05 is recommended to corroborate maximal effort, despite RER being sensitive to test format and modality. PURPOSE: We therefore examined whether a ramp-incremental (RI) step-exercise (SE) test (RISE; Rossiter et al. J Appl Physiol 100: 764-, 2006) can reliably determine VO2max independent of limiting symptoms and the necessity for secondary criteria in HF patients. METHODS: Ten HF patients (NYHA class II-III) initially performed a modified Bruce treadmill test. Patients then completed a symptom limited RISE95 cycle ergometer test in the format: RI (4-12 W.min-1); 5 min recovery at 10W; SE at 95% of peak RI work rate. VO2, RER, and ventilation (VE) were measured breath-by-breath using a mass spectrometer and turbine (MSX, NSpire, UK). Ratings of 'breathlessness' and 'leg effort' were measured on a visual analogue scale. Peak RI and SE values were compared using 95% confidence intervals (CI95) over 20 s. RESULTS: VO2peak was similar in treadmill and cycle exercise (15.3 ± 3.2 vs 15.1 ± 3.9 mL.kg-1.min-1 respectively), but RER was greater in cycling (1.04 ± 0.05 vs 1.14 ± 0.1; p<0.05). Within-patient comparison of CI95 for VO2peak in RISE95 revealed VO2max in 8/10 participants. At intolerance in RI, leg effort was greater than breathlessness (83 ± 15 vs 73 ± 19 %; p<0.05), but ratings in SE were dissociated from the point of limitation by 11 ± 5 %. CONCLUSIONS: The RISE95 test was well tolerated by HF patients and confirmed VO2max in 8/10 independent of RER and symptom severity. Importantly, RER was >1.05 in the 2 patients in whom VO2max was not confirmed, further questioning the efficacy of this criterion. Symptom severity differed between RI and SE by >10%, despite VO2max being achieved in both. These data suggest that the RISE95 test can delineate between VO2peak and VO2max, even in HF patients where exercise-induced sensations of fatigue and dyspnea are exacerbated. Supported by MCRC Leeds; ORSAS UK (DTC); MRC UK (TSB)