Patients with systemic lupus erythematosus (SLE) experience excessive, debilitating fatigue with previously reported evidence of etiologically mediated cardiorespiratory impairments. Performance fatigability provides a precise characterization of fatigue as it can be quantified objectively as a function of time, frequency, and/or duration. Nevertheless, little consideration has been given to understanding performance fatigability and its physiological determinants in those with SLE. The purpose of this study was to characterize performance fatigability in patients with SLE, using measures surrounding the anaerobic threshold, with emphasis on cardiorespiratory impairment as a potential mediating factor.
This was a case–control study design. 44 physically inactive women, 26 with SLE and 18 controls, completed a treadmill cardiopulmonary exercise test to volitional exhaustion.
There were no significant differences in age (SLE 34.8(9.0) versus control 36.9(7.3) years; P = .422) between groups. Body mass index (SLE 27.1(5.4) versus control 23.8(5.2) kg/m2; P = .045) was significantly higher in the SLE versus control group. Resting heart rate (SLE 68(16) versus control 78(15) bpm; P = .040) was significantly lower in the SLE compared with the control group. The VO2 corresponding to the anaerobic threshold (AT-VO2), used to identify the onset of exercise-induced fatigue, was significantly lower in women with SLE than in controls (SLE 12.4(3.1) versus control 16.4(2.2) ml/kg/min; P < .001), as was AT-stage (SLE 2.5(0.90) versus control 3.4(0.78); P = .002). In addition, the Fatigue Severity Scale (FSS) score was highly and inversely correlated with AT-VO2 (rho = −0.615; P < .001), and FSS was highly correlated with the functional aerobic impairment index (rho = 0.663; P < .001).
This study underscores severe performance fatigability in patients with SLE and its link to cardiorespiratory insufficiency. Physiological presentation of performance fatigability was observed during very low intensities of exercise, emphasizing the negative impact it may have on physical function in this population.