Dysfunctional breathing is a common and clinically relevant problem in patients with chronic obstructive pulmonary disease (COPD), contributing to increased dyspnea perception, reduced exercise tolerance, and impaired quality of life. The Nijmegen Questionnaire (NQ) is a widely used symptom-based instrument for screening dysfunctional breathing; however, a validated Turkish version for patients with COPD is currently unavailable.

This observational methodological study aims to translate, culturally adapt, and evaluate the validity and reliability of the Turkish version of the Nijmegen Questionnaire (NQ-TR) in individuals with stable COPD.

This single-center observational study will be conducted in patients with clinically stable COPD. The study consists of two main phases: (1) translation and cultural adaptation of the Nijmegen Questionnaire following international guidelines for patient-reported outcome measures, and (2) psychometric evaluation of the Turkish version in a COPD population.

The translation process includes forward translation, reconciliation, back-translation, developer review, cognitive debriefing with patients, and final proofreading. After completion of the linguistic adaptation, the NQ-TR will be administered to eligible participants at baseline and repeated after one week in clinically stable individuals to assess test-retest reliability.

Construct validity will be evaluated using exploratory and confirmatory factor analyses. Convergent validity will be assessed by examining correlations between NQ-TR scores and established clinical measures, including the COPD Assessment Test (CAT), Modified Medical Research Council (mMRC) Dyspnea Scale, Hospital Anxiety and Depression Scale (HADS), and Dyspnea-12 (D-12). Internal consistency, test-retest reliability, and measurement stability will be analyzed.

Inclusion Criteria:

• Adults aged 18 years and older
• Diagnosis of COPD confirmed according to GOLD criteria
• Clinically stable disease (no acute exacerbation or hospitalization within the last 4 weeks)
• Ability to read and understand Turkish
• Willingness to participate and provide written informed consent

Exclusion Criteria:

• Acute COPD exacerbation or respiratory infection within the previous 4 weeks
• Presence of severe cardiac, neurological, or systemic disease affecting questionnaire responses
• Coexisting pulmonary conditions such as bronchiectasis, lung cancer, prior pulmonary tuberculosis, pleural disease, or history of lung surgery
• Moderate to severe cognitive impairment or communication difficulties
• Severe visual or hearing impairment preventing questionnaire completion
• Pregnancy
• Refusal to participate or withdrawal during the study

The study population consists of adults aged 18 years and older with a confirmed diagnosis of chronic obstructive pulmonary disease (COPD) according to GOLD criteria. Eligible participants are clinically stable patients attending the pulmonology outpatient clinic of a tertiary care hospital, with no acute exacerbation or hospitalization within the previous four weeks. All participants are Turkish-speaking, able to complete self-reported questionnaires, and provide written informed consent.