Functional Capacity Incorporating Dynamic Ventilation in Systemic Sclerosis: Agreement Analysis Between Performance on the 6-Minute Walk Test and Glittre-ADL Test.

Abstract

Background: Functional capacity at submaximal exercise levels has become more popular as an outcome measure in systemic sclerosis (SSc). However, it is necessary to know the ventilatory requirements of the different field tests.

Objectives: To verify the agreement of the ventilatory dynamics measured at submaximal exercise between the the Glittre-ADL test (TGlittre) and the 6-min walk test (6MWT) and, secondarily, to evaluate the correlations of these measurements with clinical and functional variables in women with SSc (wwSSc).

Methods: This was a cross-sectional study in which 30 wwSSc underwent the 6MWT and TGlittre while hooked to a device reading their ventilatory demand. Physical function was assessed on the Health Assessment Questionnaire Disability Index (HAQ-DI), and lung function was assessed by spirometry.

Results: The median 6-min walking distance (6MWD) was 344 (282-410) metres, and 25 (83.3%) participants did not reach 80% of the predicted distance. The median TGlittre time was 147 (107-188) seconds, and 18 (60%) participants exceeded 120% of the predicted time. There was agreement between the two tests on the following variables: heart rate (ICC = 0.883, P < 0.0001), breathing reserve (ICC = 0.816, P < 0.0001), peripheral oxygen saturation (ICC = 0.752, P = 0.0009), inspiratory capacity (ICC = 0.690, P < 0.0001), and peak minute ventilation (ICC = 0.433, P = 0.007). There was a weak correlation between 6MWD and TGlittre time (r_s=-0.353, P = 0.05). 6MWD correlated significantly with the HAQ-DI score (r_s=-0.606, P = 0.0004) and forced vital capacity (FVC, r_s= 0.427, P = 0.018). TGlittre time correlated significantly with HAQ-DI (r_s= 0.440, P = 0.015) and FVC (r_s=-0.404, P = 0.026).

Conclusion: In wwSSc, the 6MWT and TGlittre have almost the same ventilatory requirements, although these patients perform worse in the 6MWT. 6MWD and TGlittre time are weakly correlated. Both 6MWD and TGlittre time are associated with physical function and lung function. Therefore, both tests should be used in clinical practice for the monitoring of these patients as they are complementary.