Impaired Oxygen Uptake Recovery Is Associated With Disease Severity In Systemic Sclerosis.

Systemic sclerosis (SSc) is a multisystem autoimmune disease with near-universal cardiopulmonary involvement. Delayed VO2 recovery measured by cardiopulmonary exercise testing (CPET) is a biomarker of disease severity in heart failure but has not been investigated in SSc. PURPOSE: To assess VO2 recovery and its associations with disease severity in SSc. METHODS: Thirty-three SSc patients (73% female, mean age 55 ± 8 yrs) free of clinical SSc cardiac involvement, completed CPET on an upright cycle ergometer. VO2peak was defined as the highest 30s rolling average value during exercise. VO2recovery was assessed by calculating VO2 at 30s post exercise as a percentage of VO2peak (VO2R). All patients underwent spirometry, resting cardiac MRI with T1 mapping, and skeletal muscle MRI. Associations between VO2R and features of SSc were evaluated with linear regression analysis. RESULTS: All participants had normal resting cardiac function. The mean VO2peak was 19.1 ± 5.0 mL/kg/min and mean %VO2predicted was 70 ± 19%. Median VO2R was 86% (range 42-136%). Five patients (15%) had a VO2R ≥ 100%, indicating abnormal oxygen metabolism that partially resolved upon cessation of exercise (Figure 1). These participants had lower exercise capacity compared to the rest of the cohort (%VO2predicted 53 ± 13% vs 73 ± 18% p = 0.03). Higher VO2R was associated with features of more severe SSc, including total Medsger Severity Score (r = 0.36 p = 0.04), more extensive skin thickening (r = 0.53 p < 0.01), skeletal muscle oedema and fatty infiltration (r = 0.36 p = 0.05 and r = 0.42 p = 0.02), and exercise impairment as %VO2predicted (r = -0.59 p < 0.01). No parameters of resting cardiac or respiratory function or burden of myocardial fibrosis were associated with VO2R (all p > 0.05). CONCLUSIONS: Delayed VO2 recovery in SSc is associated with exercise intolerance and skeletal muscle imaging abnormalities. A distinctive post-exercise increase in VO2 may be a biomarker of more severe SSc.