Objective: To determine if fatigue is associated with diminished aerobic capacity in women with systemic lupus erythematosus (SLE).
Methods: Eighteen women (age 35 +/- 9 years) with mild SLE (Systemic Lupus Activity Measure = 3.1 +/- 2.1) and 16 healthy but sedentary controls (age 38 +/- 8 years) completed peak treadmill exercise tests to determine aerobic capacity and Fatigue Severity Scales to quantify the severity of fatigue. Measures of oxygen consumption (VO(2)) were recorded during the treadmill tests.
Results: Peak VO(2) was lower in patients with SLE (19.2 +/- 4.4 ml/kg/minute) as compared with controls (27.4 +/- 4.7 ml/kg/minute) and expected values (30.7 +/- 3.1 ml/kg/minute; P < 0.0006 versus controls and P < 0.0001 versus expected). Functional aerobic impairment was observed in 14 of the 18 patients with SLE. In patients with SLE, ventilatory threshold, a marker for the onset of lactic acidemia, was observed at the lowest energy requirement for instrumental activities of daily living. Peak VO(2) in the patients with SLE was similar to the highest energy requirements for instrumental activities of daily living, leaving little or no reserve for more intense occupational and recreational activities. Peak VO(2) was significantly higher (P < 0.0001) than the activity of daily living requirements in controls, providing a substantial energy reserve. Fatigue severity score (FSS) was 5.0 +/- 1.4 in patients with SLE, with 14 of the 18 patients having scores above 4.0, a score indicating that fatigue severity limited physical activity. Of the 14, 12 had functional aerobic impairment. An FSS of greater than 4.0 was not observed in controls (mean = 2.5 +/- 0.7).
Conclusion: In women with SLE, aerobic capacity was diminished to levels that were insufficient for engaging in activities of daily living and below those expected to result from physiologic deconditioning. This functional aerobic impairment was strongly correlated with the perception of severe, activity-limiting fatigue.