Respiratory Function and S-index in Radiographic Axial Spondyloarthritis

March 31, 2026 updated by: Ayse BOZDAS, Gazi University

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

Study Overview

Status

Completed

Conditions

Detailed Description

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.

Study Type

Observational

Enrollment (Actual)

52

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Turkey (Türkiye)
      • Ankara, Turkey (Türkiye), 06560
        • Gazi University Hospital, Department of Physical Medicine and Rehabilitation

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Sampling Method

Non-Probability Sample

Study Population

The study population consisted of patients diagnosed with radiographic axial spondyloarthritis who were followed at the Department of Physical Medicine and Rehabilitation at Gazi University, and healthy volunteers recruited from the same institution.

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Radiographic Axial Spondyloarthritis (r-axSpA) Group
Individuals diagnosed with radiographic axial spondyloarthritis according to the Assessment of SpondyloArthritis international Society (ASAS) criteria, who were followed at the Department of Physical Medicine and Rehabilitation at Gazi University. Participants underwent standardized assessment of chest expansion, spirometric parameters, inspiratory muscle strength using the S-index, and clinical indices including BASDAI, BASFI, and BASMI
Healthy Control Group
Healthy individuals without a diagnosis of axial spondyloarthritis. Participants will undergo assessment of chest expansion, spirometric parameters, and inspiratory muscle strength using the S-index.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
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.
Baseline

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
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).
Baseline
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.
Baseline
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.
Baseline
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.
Baseline
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.
Baseline

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Gazi University

Investigators

  • Study Director: Feride N Gogus, MD, Gazi University Faculty of Medicine

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

January 3, 2025

Primary Completion (Actual)

October 28, 2025

Study Completion (Actual)

October 28, 2025

Study Registration Dates

First Submitted

March 25, 2026

First Submitted That Met QC Criteria

March 31, 2026

First Posted (Actual)

April 7, 2026

Study Record Updates

Last Update Posted (Actual)

April 7, 2026

Last Update Submitted That Met QC Criteria

March 31, 2026

Last Verified

March 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • Gazi R-axSpA S-index

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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