Radiographic axial spondyloarthritis (r-axSpA) is a chronic inflammatory disease that may lead to reduced chest expansion and impaired respiratory function due to thoracic involvement. While inspiratory muscle strength is commonly assessed using maximum inspiratory pressure (MIP), the S-index is a novel parameter reflecting dynamic inspiratory muscle strength and has not yet been investigated in this population.
This study aims to compare chest expansion, spirometric parameters, and S-index values between individuals with r-axSpA and healthy controls. Additionally, the relationships between these parameters and clinical indices (BASDAI, BASFI, and BASMI) will be evaluated in patients with r-axSpA. The study also aims to explore the potential role of the S-index in the assessment of pulmonary function in this patient group.