Predicting peak oxygen uptake from 6-min walk test performance in male patients with left ventricular systolic dysfunction

BACKGROUND: In patients with left ventricular systolic dysfunction (LVSD), peak oxygen uptake (pVO2) has strong predictive power for mortality, and can be used to guide management. However, many patients cannot tolerate standard test protocols. The 6-min walk test (6-MWT) is often used to estimate functional capacity due to its simplicity, cost effectiveness and familiarity to patients with LVSD. The relationship between 6-MWT performance and pVO2 is not certain, but if closely related could allow substitution of an expensive and cumbersome test for a cheaper and more familiar one. METHODS AND RESULTS: 120 male patients with LVSD (LVEF <40%; (mean+/-S.D.) age 68+/-13 years; BMI 28+/-5) performed, in random order, a maximal incremental treadmill exercise test with metabolic gas exchange measurements to derive peak oxygen consumption (pVO2 = 19.8+/-5.8 mL.kg(-1).min(-1)), and a standardised 6-MWT (308+/-142 m; r = 0.44; P = 0.00001). In multivariate models including demographic data, resting blood pressure and heart rate, spirometry, routine blood samples, and walk distance, five variables were independently predictive of peak oxygen consumption. pVO2 = 11.92 + (1.48 x FEV1 (L)) + (1.12 x haemoglobin (g dl(-1))) + (0.016 x distance walked (m)) - (0.33 x BMI) - (0.11 x age (years)). This equation accounted for 48% of the variation in pVO2. CONCLUSIONS: Using these five simple variables, peak oxygen consumption can be estimated with moderate accuracy. In clinical practice, however, when an estimate of peak oxygen consumption is required, incremental exercise testing with metabolic gas exchange measurements cannot be avoided in male patients with LVSD. Further work is needed to assess the relation between estimated pVO2 and outcome.