Aerobic capacity in patients with rheumatoid arthritis: a comparison of two submaximal test methods

BACKGROUND

In a clinical setting it is important to evaluate aerobic capacity in individuals with rheumatoid arthritis (RA) and to have a choice between tests, owing to disability of varying severity. Two submaximal tests, a bicycle ergometer test and a treadmill walking test, are commonly used. Despite expected differences in the results, these tests have been used interchangeably. The aim of the current study was to compare the results of the two tests, the size of the difference and factors expected to influence the results.

METHODS

Fifty-two outpatients with RA performed the two tests. Agreement and correlations between the results of the tests were calculated. Multivariate analysis was used to study the relationships between gender, weight, health assessment questionnaire, global health assessment and the difference between the tests.

RESULTS

Sixty per cent of the subjects exhibited a higher estimated value of maximum oxygen uptake (VO(2max)) in the treadmill test. The limits of agreement for the estimated VO(2max) values between the two methods ranged from -13.4 to +18.4 ml x min(-1) x kg(-1), and the intraclass correlation coefficient (ICC(Two-way mixed)) was 0.34 (95% confidence interval [CI] 0.07, 0.56). Body weight was independently associated with the difference between the two tests (regression coefficient 0.3; 95% CI 0.14, 0.42). A higher body weight had a greater impact on the results of the bicycle test (R(2) = 0.28; regression coefficient -0.3; 95% CI -0.47, -0.17) than on the treadmill walking test (R(2) = 0.02; regression coefficient -0.06; 95% CI -0.14, 0.03).

CONCLUSIONS

It is not advisable to use the two submaximal methods interchangeably. Weight influenced the difference between the two tests, and to a higher degree in the bicycle test than the treadmill walking test.

Reliability and validity of the Fatigue Severity Scale in Swedish for patients with systemic lupus erythematosus

OBJECTIVE

The aim was to translate, test, and describe aspects of reliability and validity of the Fatigue Severity Scale (FSS) in Swedish (FSS-Swe) in patients with systemic lupus erythematosus (SLE).

METHODS

Patients with stable SLE, low or moderate disease activity, and low organ damage were included. Forward and back translations of the FSS were performed. Construct validity was tested with 32 women using a first Swedish translation. Feasibility, ceiling and floor effects, internal consistency, test-retest reliability, and content validity were tested on a slightly modified final version of the FSS-Swe in a non-selected group of patients (n = 23).

RESULTS

There were correlations (p< or =0.05) between the FSS-Swe and overall disease activity according to the Systemic Lupus Activity Measure (SLAM) (r(s) = 0.48) and the SLAM Visual Analogue Scale (SLAM-VAS) (r(s) = 0.46); between the FSS-Swe and eight subscales of the Swedish 36-Item Medical Outcomes Study Short-Form Health Survey (SF-36) (r(s) = -0.41 to -0.65) and between the FSS-Swe and age (r(s) = -0.35). All patients answered all FSS-Swe questions at both test and retest. There was one ceiling effect in one question on one occasion. The Kolmogorov-Smirnov test indicated normal distribution. Cronbach's alpha was 0.94 and corrected item-to-total correlation exceeded 0.3. There were no significant systematic test-retest differences, and the median-weighted kappa coefficient was 0.75. Twenty patients understood the questions in FSS-Swe, 18 considered they were relevant, reflected their fatigue, and that none should be excluded. Five items were suggested to be included.

CONCLUSIONS

The FSS-Swe supports construct validity, is feasible, has no important ceiling or floor effects, has satisfactory internal consistency, substantial test-retest reliability, and satisfactory content validity in the SLE patients studied. However, its sensitivity to change needs to be tested.

Aerobic capacity correlates to self-assessed physical function but not to overall disease activity or organ damage in women with systemic lupus erythematosus with low-to-moderate disease activity and organ damage

The present aim is to investigate the relationships between aerobic capacity and disease activity, organ damage, health-related quality of life (HRQL) and physical activity in 34 women with systemic lupus erythematosus (SLE) with low-to-moderate disease activity and organ damage. Mean age was 51 (SD 10) years, disease duration 17 (SD 11) years. Aerobic capacity (maximal oxygen uptake/VO2 max) was measured with a bicycle ergometer exercise test. Overall disease activity was assessed with Systemic Lupus Activity Measure (SLAM) and the modified Systemic Lupus Erythematosus-Disease Activity Index (modified SLE-DAI), overall organ damage with the Systemic Lupus International Collaboration Clinics/American College of Rheumatology-Damage Index, [SLICC/(ACR)-DI], HRQL with the 36-item Short-form health-survey (SF-36) and physical activity with a self-assessed question. The women who were low-to-moderately physically active had 89-92% (P < or = 0.001) of VO2 max predicted for sedentary women. Maximal oxygen uptake (L/min, mL/min/kg) correlated to SF-36 physical function (rs = 0.49, rs = 0.72) (P < or = 0.01), but not (rs < or = 0.25) to other HRQL scales, overall disease activity or organ damage or physical activity. The correlation between aerobic capacity and physical function and the absence of correlation between aerobic capacity and physical activity, suggest a possible disease-related factor behind the low aerobic capacity. However, with no correlation between aerobic capacity and overall disease activity and organ damage, low physical activity may contribute to the low aerobic capacity in our sample.

Reference values for the physical work capacity on a bicycle ergometer for men -- a comparison with a previous study on women

The aim of the study was to collect new reference values for the clinical ramp exercise test on bicycle, because in our experience, the commonly used values were too low. A group of healthy men (n = 81, 20-80 years) was randomly selected from the local municipal register to achieve an even distribution in age. Data were compared with those obtained in a similar, previous study on women (n = 87). The subjects were encouraged to cycle until exhaustion (19 on the Borg scale) when maximal load, heart rate and systolic blood pressure were recorded. Maximal load (W(max)) was related to age (years) and height (m) using a non-linear function: W(max) = (244.6 x height - 92.1)/[1 + exp[0.038 x (age - 77.3)]]. Maximal heart rate (HRmax) was described by a similar function: HRmax = 203.7/[1 + exp[0.033 x (age - 104.3)]]. The maximal systolic blood pressure (BP(max)) was described by a linear function based on age: BP(max) = 0.505 x age + 192. Similar functions for the women are also given. It is suggested that 80-120% of the predicted maximal load can be taken as a reference interval for both men and women and similarly 90-110% of the maximal heart rate. In this study, 84% of the men reached a maximal load within the reference interval and 93% maximal heart rate within the reference interval. The reported values for maximal load were 104-132% of the reference values published by others.

Repeatability of measurements of oxygen consumption, heart rate and Borg's scale in men during ergometer cycling

The coefficient of repeatability (COR), expressed as 2-SD of differences, was calculated between two measurements of oxygen consumption (V O2), heart rate (HR) and rating of perceived exertion (RPE) during ergometer cycling by men. The two sets of measurements were performed 5 to 6 weeks apart. Nineteen healthy men performed an incremental maximal exercise test on an ergometer cycle. The load started at 50 W and increased by 5 W 20 s-1 until exhaustion was reached. At 40% of the individual maximum load of the pretest, the load was kept constant for 4 min in order to reach steady state. Gas measurements were recorded continuously by computerized instrumentation. The HR was monitored with electrocardiography (ECG) and the perceived exertion was evaluated using Borg's scale. The COR of V O2 at sub-maximal load was 14% and at maximum load 11%. The values in absolute figures were 209 and 332 ml min-1. The corresponding COR of the HR was 16% at sub-maximum load and 6% at maximum load, and an evaluation of the perceived exertion yielded CORs in absolute values of 4.8 and 1.3, respectively. The COR for V O2, HR and ratings of perceived exertion when cycling on an ergometer cycle thus indicate a better agreement between the measurements at maximum load. The COR of the heart at sub-maximal loads must be kept in mind when using HR for estimation of V O2max. The reported findings should be considered when using tests on an ergometer cycle for evaluating exercise capacity.