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NCT Number: NCT07515131

Respiratory Function and S-index in Radiographic Axial Spondyloarthritis

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.

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Key information

Conditions

Radiographic Axial Spondyloarthritis Ankylosis Arthritis Axial Spondyloarthritis Bone Diseases Joint Diseases Musculoskeletal Diseases Pathologic Processes Pathological Conditions, Signs and Symptoms Respiration Disorders Respiratory Aspiration Respiratory Tract Diseases Spinal Diseases Spondylarthritis Spondylarthropathies Spondylitis Spondylitis, Ankylosing

Age range

18 year and older

Sex eligibility

All sexes

Study type

Observational

Primary location

Gazi University Hospital, Department of Physical Medicine and Rehabilitation

Ankara, 06560, Turkey (Türkiye)

About this study

Radiographic axial spondyloarthritis (r-axSpA) is a systemic, chronic inflammatory rheumatic disease strongly associated with HLA-B27, primarily affecting the sacroiliac joints and the axial skeleton. Its prevalence in the general population ranges between approximately 0.1% and 1.4%. In patients with r-axSpA, involvement of the costovertebral and costosternal joints, as well as the entheses in the thoracic region, may lead to progressive ankylosis over time. This process results in reduced thoracic mobility, decreased chest expansion in the early stages, and a predominantly restrictive pattern of respiratory dysfunction.

Previous studies have investigated the relationships between chest expansion, aerobic capacity, and spirometric parameters with disease activity, functional status, and spinal mobility, as assessed by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), and Bath Ankylosing Spondylitis Metrology Index (BASMI), in individuals with r-axSpA.

Maximum inspiratory pressure (MIP) is widely used for the static assessment of inspiratory muscle strength and has been evaluated in conjunction with chest expansion and spirometric parameters in several studies. In contrast, the S-index is a relatively novel parameter that reflects inspiratory muscle strength dynamically and has not yet been investigated in patients with r-axSpA. Although previous studies have demonstrated moderate to strong correlations between S-index and MIP, these measures represent different physiological aspects of respiratory muscle function and therefore do not yield identical results.

The present study aims to compare chest expansion, spirometric parameters, and S-index values between individuals with r-axSpA and healthy controls. In addition, within the r-axSpA group, the relationships between these parameters and clinical indices (BASDAI, BASFI, and BASMI) will be examined.

Furthermore, the discriminative ability of chest expansion, spirometric parameters, and the S-index in distinguishing individuals with r-axSpA from healthy controls will be evaluated. As a distinctive aspect of this study, S-index values will be analyzed both in comparison between groups and in relation to spirometric parameters, chest expansion, and clinical indices in patients with r-axSpA.

This study is expected to provide novel evidence regarding the potential role of the S-index in the assessment of pulmonary function in patients with r-axSpA.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Willingness to participate in the study and provide informed consent
  • Age ≥18 years
  • Absence of any known chronic disease (for the healthy control group)
  • Diagnosis of radiographic axial spondyloarthritis according to the Assessment of SpondyloArthritis international Society (ASAS) criteria and absence of any additional chronic disease (for the r-axSpA group)

Exclusion criteria

  • Presence of known cardiopulmonary disease
  • Presence of any rheumatologic disease other than radiographic axial spondyloarthritis (r-axSpA)
  • Inability to cooperate with testing procedures
  • Presence of chest wall or spinal deformities that may restrict lung capacity (e.g., pectus carinatum, pectus excavatum, scoliosis)
  • Professional athletes

Treatment and study plan

Primary outcomes

  1. Inspiratory muscle strength assessed by S-index

    Time frame: Baseline

    S-index was measured using the PowerBreathe K5 device (PowerBreathe International Ltd., UK). The test assesses inspiratory muscle strength based on flow and pressure during dynamic inspiration from residual volume to total lung capacity. Measurements were performed under standardized conditions (same device, operator, afternoon hours, 20-25°C). Participants were seated upright with a nasal clip and instructed to perform maximal and rapid inspiratory efforts against resistance after normal expiration. Eight maneuvers were performed in 2-3 sets with ≥30-second rest intervals. The test was considered valid if the difference between the highest three values was <10%, and the highest value was used for analysis.

Secondary outcomes

  1. Pulmonary function parameters (FVC, FEV1, FEV1/FVC, PEF)

    Time frame: Baseline

    Spirometry was performed using a Cosmed device (Omnia, Italy) following calibration before each test. Participants were seated upright with a nasal clip and instructed to perform maximal inspiration followed by forced expiration. Measurements were conducted under standardized conditions (same operator, afternoon hours, 20-25°C). At least three acceptable maneuvers were obtained, and the highest value was recorded if variability was <10%. Up to eight maneuvers were performed with ≥30-second rest intervals. Measurements were evaluated according to ATS/ERS criteria. Parameters recorded included FEV1, FVC, FEV1/FVC, and peak expiratory flow (PEF).

  2. Chest expansion

    Time frame: Baseline

    Chest expansion was measured using a tape measure at the level of the 4th intercostal space with the participant in an upright position. The difference in chest circumference between maximal inspiration and maximal expiration was recorded as chest expansion. Measurements were performed twice, and the highest value was used for analysis.

  3. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)

    Time frame: Baseline

    Disease activity was assessed using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), a validated 0-10 visual analog scale (VAS)-based instrument consisting of six items evaluating fatigue, spinal pain, peripheral joint symptoms, enthesitis, and morning stiffness. Higher scores indicate greater disease activity.

  4. Bath Ankylosing Spondylitis Functional Index (BASFI)

    Time frame: Baseline

    Functional status was assessed using the Bath Ankylosing Spondylitis Functional Index (BASFI), a validated 0-10 visual analog scale (VAS)-based instrument consisting of ten items evaluating functional limitations in daily activities. Higher scores indicate greater functional impairment.

  5. Bath Ankylosing Spondylitis Metrology Index (BASMI)

    Time frame: Baseline

    Spinal mobility was assessed using the Bath Ankylosing Spondylitis Metrology Index (BASMI), which evaluates five clinical parameters including lateral lumbar flexion, tragus-to-wall distance, modified Schober test, intermalleolar distance, and cervical rotation. Scores range from 0 to 10, with higher scores indicating greater mobility limitation.

Sponsors and collaborators

Lead sponsor

Gazi University

Other

Registry information

Official study title

Chest Expansion, Pulmonary Function, and Dynamic Inspiratory Muscle Strength (S-index) in Patients With Radiographic Axial Spondyloarthritis

Important dates

Study start
2025
Primary completion
2025
Study completion
2025
First posted
Apr 7, 2026
Registry last updated
Apr 7, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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