**Background:** Chronic obstructive pulmonary disease (COPD) is characterized by airflow limitation and persistent respiratory symptoms, leading to decreased functional performance and quality of life. The Theory of Unpleasant Symptoms posits that physiological, psychological, and situational factors influence symptom experience, which in turn affects performance. This study aimed to build and test a structural equation model predicting functional performance in COPD patients by examining relationships among disease severity (physiological factor), uncertainty (psychological factor), social support (situational factor), symptom experience, coping, and functional performance.
**Methods:** A model-testing design was used. Subjects were recruited via convenience sampling from outpatient pulmonary clinics at a general hospital in Seoul, Korea. Inclusion criteria: diagnosed with COPD by a pulmonary specialist, ≥18 years old, diagnosed >3 months prior, and had spirometry results within the past 3 months. Exclusion criteria: dementia/cognitive impairment, heart failure, or diagnosis of common cold, pneumonia, or lung cancer. Data were collected from July 2018 to April 2019 using validated instruments. Of 210 enrolled patients, 202 were analyzed (8 excluded for missing responses). Instruments included: FEV1% predicted for disease severity; Mishel's Uncertainty in Illness Scale-Community Form (MUIS-C) for uncertainty; Multidimensional Scale of Perceived Social Support (MSPSS) for social support; Revised Memorial Symptom Assessment Scale (RMSAS) for symptom experience; Coping Strategy Indicator (CSI) for coping (problem-solving and social support seeking subscales); and Functional Performance Inventory-Short Form (FPI-SF) for functional performance. Data were analyzed using IBM SPSS v27.0 and Mplus 8.0 with full-information maximum likelihood estimation. Model fit was assessed using χ², normed χ², CFI, SRMR, and RMSEA. Mediating effects were tested via bootstrapping.
**Key Results:** The mean age was 68 years; 92.1% were male; 57.4% had GOLD 2 airflow limitation. Mean FEV1% predicted was 59.75 ± 18.98%. The final model demonstrated good fit: normed χ² = 1.705, CFI = 0.935, SRMR = 0.059, RMSEA = 0.055. Symptom experience was significantly reduced by lower uncertainty (β = 0.236, p = 0.009) and higher social support (β = −0.200, p = 0.044); disease severity was not significantly associated with symptom experience (β = −0.025, p = 0.745). These variables explained 11.9% of variance in symptom experience. Coping was significantly higher with greater social support (β = 0.278, p = 0.012) and greater symptom experience (β = 0.172, p = 0.047); disease severity and uncertainty were not significant predictors. These variables explained 9.4% of variance in coping. Functional performance was significantly higher with lower disease severity (β = 0.238, p < 0.001), lower uncertainty (β = −0.164, p = 0.021), and lower symptom experience (β = −0.558, p < 0.001); social support and coping were not significant direct predictors. These variables explained 51.8% of variance in functional performance. Bootstrapping revealed a significant mediating effect: uncertainty → symptom experience → functional performance (B = −0.136, 95% CI [−0.283, −0.011]), indicating that reduced uncertainty improves functional performance by reducing symptom experience. No other mediating pathways were statistically significant.
**Clinical Implications:** The study confirms the utility of the Theory of Unpleasant Symptoms for explaining functional performance in COPD. Clinically, interventions should target reducing disease severity (e.g., smoking cessation, vaccination, early treatment), lowering uncertainty (e.g., providing clear disease information, emotional support, accessible healthcare systems), and alleviating symptom experience to improve patients' daily functioning. The significant mediating role of symptom experience between uncertainty and functional performance suggests that uncertainty-reduction programs may yield dual benefits by also lowering symptom burden. Multidisciplinary integrated treatment programs incorporating exercise, education, nutrition, and psychiatric support are recommended. Limitations include the predominantly male sample, single-center recruitment, use of only FEV1% to measure disease severity, and potential interviewer effects from one-on-one questionnaire administration.