Thursday Morning Poster Presentations: Posters displayed from 7:30 a.m.–12:30 p.m.: One-hour author presentation times are staggered from 8:30–9:30 a.m. and 9:30–10:30 a.m.: D-20 Free Communication/Poster – Clinical Exercise Testing I: THURSDAY, JUNE 1, 2006 2:00 PM – 5:00 PM ROOM: Hall B
Patients with systemic lupus erythematosus (SLE) demonstrate a lower maximal oxygen uptake (VO2max) compared to matched healthy controls, placing them at an increased risk of morbidity and mortality from cardiovascular disease, as well as contributing to the excessive fatigue and disability they experience. This supports the value of the assessment of aerobic fitness in this population. Traditional methods to assess VO2max require specialist equipment, and are often expensive, time consuming and requires high motivation and effort from the subject.
PURPOSE: To assess the reliability and validity of a simple, sub-maximal exercise test for the estimation of maximal oxygen uptake in patients with SLE, the Siconolfi step-test (SST).
METHODS: Twenty patients with mild SLE were recruited for the study with two excluded for failing to meet the ACSM criteria for the attainment of VO2max leaving 18 patients for whom the analysis was performed (Mean ± SD; age = 49.9 ± 13.2 yr, mass = 71.7 ± 13.8 kg, VO2max = 23.5 ± 4.9 ml/kg/min, disease duration = 11.3 ± 10.4 yr). Patients performed two trials of the SST separated by 3–7 days with VO2max estimated using the Åstrand-Ryhming nomogram. The SST was validated against directly measured VO2max, which was assessed using a continuous incremental test on a cycle ergometer to volitional exhaustion. Expired gas was analyzed using a breath-by-breath online system.
RESULTS: Reliability. Estimated VO2max of the two trials of the SST were highly related (r = 0.92, P <0.001), with a non-significant bias ± 95% limits of agreement (LoA) of 0.05 ± 3.9 ml/kg/min. Validity. Both trials of the SST were significantly related to actual VO2max (r = 0.71 and 0.69 for trial 1 and 2 respectively, both P <0.001) with respective standard errors of the estimate of 14.8% and 15.2%. There was no significant systematic bias between actual VO2max and either trial of the SST. For both trials of the SST, the data showed evidence of heteroscedasticity, thus underwent log transformation. This reduced heteroscedasticity with the antilogs giving a mean bias on the ratio scale x/÷ random error (95% ratio limits) of 1.037 x/÷ 1.343 (trial 1) and 1.038 x/÷ 1.339 (trial 2).
CONCLUSION: The SST appears to be reliable on a test-retest basis and although the (validity) limits of agreement of ± 34% are relatively wide, they are comparable with other frequently used sub-maximal tests. The ease of use, portability and relative in-expense of the SST makes this an attractive method to estimate VO2max in an SLE population.