Determinant factors of exercise functional capacity in the subgroup of women with scleroderma-associated interstitial lung disease without pulmonary hypertension

Abstract

Introduction: Scleroderma or systemic sclerosis (SSc) is a chronic connective tissue disease, characterized by thickening of the skin resulting from excess collagen fibers. The systemic manifestations of SSc involve pulmonary, cardiac, renal and esophageal involvement, as well as affect muscular strength, functional capacity and quality of life. Since SSC is poorly studied in rehabilitation, more detailed assessment of lung function and functional exercise capacity is critical in these patients. To date, there have been no studies evaluating the factors that determine functional capacity to exercise in the SSc subgroup associated with interstitial lung disease (SSc-ILD) without pulmonary hypertension, as well as using the single-breath nitrogen washout test (N2SBW). Objective: The main objective of the present study was to assess the impact of heterogeneity on the distribution of ventilation assessed by N2SBW and peripheral muscle dysfunction on exercise capacity in women with SSc-ILD with limited involvement of the pulmonary parenchyma. As secondary objectives, this study aimed: 1) to compare the performance of women with SSc and healthy women in relation to pulmonary function, exercise capacity, peripheral muscular dysfunction, and health-related quality of life (HRQoL); 2) to correlate functional exercise capacity with pulmonary function and peripheral muscle dysfunction; 3) to correlate pulmonary function with peripheral muscular dysfunction; and 4) to correlate the HRQoL of patients with SSc with functional capacity to exercise, pulmonary function, and peripheral muscular dysfunction. Methods: This was a cross-sectional study of 20 women with SSc-ILD in outpatient treatment. The control group (20 women) consisted of healthy volunteers, who were matched for age, gender, body mass, height, and body mass index. The pulmonary function tests, the six-minute walk test (6MWT) and the assessment of quadriceps muscle strength were performed through isometric quadriceps dynamometry. In addition, quality of life assessment was performed through the Health Assessment Questionnaire Disability Index (HAQ-DI). Results: In this analysis, the distance traveled during the 6MWT (6MWD) correlated moderately with the phase III slope of N2SBW (phase III slopeN2SBW) (r=-0.675, P=<0001) and forced vital capacity (FVC) (r=0.520, P=0.0005), and reasonably with pulmonary diffusion capacity to carbon monoxide (DLco) (r=0.387, P=0.013). On the other hand, the peripheral oxygen saturation (SpO2) did not present a statistically significant correlation with any of the parameters of pulmonary or muscular function. The correlation between 6MWTD and ΔSpO2 was not significant (r=-0.270, P=0.092). In addition, we investigated whether pulmonary function and muscle function variables could independently predict performance during the 6MWT. In this analysis, phase III slopeN2SBW was the only independently predictive variable for the 6MWT ', while quadriceps strength and FVC / DLco ratio were the independent predictive variables for ΔSpO2. In conclusion, the present study shows that, in the subgroup exclusively composed of women with SSc-ILD, there is a heterogeneity in the distribution of ventilation, which explains much of the shorter distance covered during the 6MWT. In addition, muscle dysfunction and abnormality in lung diffusion explain at least in part the oxygen desaturation of these patients during the 6MWT. Conclusion: With the results of this research, perspectives are opened to accompany the new strategies of treatment of the patients with SSc that are appearing in recent years.