Cardiopulmonary exercise testing for peak oxygen uptake (VO2peak) is widely used to evaluate severity, pathophysiology and prognosis in patients with chronic heart failure (CHF). A VO2peak ≤14 (or 12 with β-blocker) ml/kg/min is associated with increased mortality and is a key criterion for cardiac transplant listing. A symptom-limited exercise test, however, may elicit a VO2peak lower than the maximum physiological limit (VO2max); the latter commonly “confirmed” using the secondary criterion of respiratory exchange ratio (RER) >1.05. RER, however, is sensitive to the test format. We, therefore, determined if a ramp-incremental (RI) step-exercise (SE) (or RISE) test could determine VO2max in CHF patients without using RER, by satisfying the criterion that two different work rates are terminated at the same VO2peak. Twenty-one male CHF patients (NYHA class I: n=3, II: n=16, and III: n=1) initially performed a modified Bruce treadmill test. Patients then completed a symptom-limited RISE95 cycle ergometer test in the format: RI (4–18 W/min; ∼10 min); 5-min recovery (10 W); SE (95% of peak RI work rate). Thirteen of these patients also performed RISE95 tests using slow (RI 3–8 W/min; ∼15 min) and fast (RI 10–30 W/min; ∼6 min) ramp rates. VO2 and RER were measured breath-by-breath by a mass spectrometer and turbine (MSX, NSpire, UK). Peak VO2 and RER were compared within-subjects, between RI and SE, by unpaired t test of the final 12 breaths of exercise. This approach allowed VO2max and its associated 95% confidence limits to be estimated. VO2peak was similar (p>0.05) in treadmill and cycle exercise (mean±SD: 16.2±2.7 vs 15.0±3.2 ml/kg/min, n=20, respectively), despite RER being greater in cycling (1.08±0.12 vs 1.15±0.09; p<0.05). As a group, VO2peak was similar (p>0.05) between RI and SE (mean±SD: 14.6±3.2 vs 14.9±3.2 ml/kg/min, n=21). A within-subject comparison, however, revealed that the VO2max criterion was met in 14 of 21 patients (measurement sensitivity range 0.6–3.8 ml/kg/min), despite RER being >1.05 in the remaining 7 (1.16±0.09). There was no effect of ramp rate on VO2peak (p>0.05), however RER was greater (p<0.05) in the fast ramp (1.24±0.09) compared to the slow (1.12±0.06). The single-visit RISE95 test incorporating incremental- and step- exercise phases, each to the volitional limit, was well tolerated by CHF patients: The SE phase was contraindicated in only 3 of the 47 tests. The RISE95 detected VO2max in 14 of 21 patients with a sensitivity of ∼10% (ie, similar to healthy subjects), and without the need for secondary criteria or incidence of false-positive. In contrast, the end-exercise RER was sensitive to both modality and ramp rate and provided a false-positive for VO2max attainment in every incidence. Therefore, the RISE95 protocol provides a robust measure of VO2max in CHF patients, to within an individually-defined CI without dependence on secondary criteria.
- respiratory exchange ratio