Systemic Sclerosis (SSc) is a connective tissue disease characterized by progressive organ fibrosis and vascular dysfunction. The leading causes of disease related morbidity and mortality are interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH). The 6-minute walk test (6MWT) is a submaximal functional exercise test used to evaluate ILD and PAH in patients with SSc. Desaturations during the 6MWT have been considered suggestive of ILD and PAH. Still, the optimal method to measure peripheral oxygen saturation during the 6MWT in patients with SSc remains unclear. Furthermore, other functional exercise tests may also be useful in patients with SSc.~Patients with SSc will perform three functional exercise tests, and approximately half of the patients will be invited to repeat the tests 1 week later to determine test-retest reliability. Additionally, nailfold videocapillaroscopy (NVC) will be performed on every patient to assess the capillary density of the nailfold of the fingers. Furthermore, to study the effect of SSc on bone, a high resolution peripheral quantitative computed tomography (HRpQCT) scan of radius and distal interphalangeal joints (DIP)/distal phalanges will be performed.~During the 6MWT, the peripheral oxygen saturation (SpO2) will be measured continuously on three anatomical locations. An arterial line will be placed, and blood will be drawn at baseline and after ended 6MWT and analysed for arterial oxygen saturation (SaO2). The correlation between the capillary density of the nailfold and the SpO2 measured on the finger will be assessed. The correlation between capillary density of the nailfold and bone status in the fingers and distal radius assessed with HRpQCT will be evaluated, and HRpQCT images will be compared with conventional radiography and DEXA. Bland-Altman plot will be used to display the agreement between SaO2 and SpO2 and between the two 6MWT. Further, the association between pulmonary variables and 6MWT results will be examined.~Two alternative functional exercise tests will be investigated and compared to results in the 6MWT: The 1-minute sit-to-stand test (1STST) and the 4-meter gait speed test (4MGS). The association between the three functional exercise tests and clinical parameters in patients with SSc will be examined.
The aim of the study is to examine the validity of peripheral oxygen saturation measurement during the 6-minute walk test in patients with Systemic Sclerosis (SSc) and to examine the utility of two other functional tests as markers of pulmonary involvement in patients with SSc.