Background: Forced expiratory volume in one second (FEV1) characterizes the pathophysiology of COPD and different trajectories of FEV1 decline have been observed in patients with COPD (e.g. gradual or episodic). There is limited information about the development of patient-reported health-related quality of life (HRQL) over the full range of the natural history of COPD. We examined the longitudinal association between change in FEV1 and change in disease-specific and generic HRQL.
Methods: We analysed data of 1734 patients with COPD participating in the COSYCONET cohort with up to 3 years of follow-up. Patients completed the Saint George's Respiratory Questionnaire (SGRQ) and the EQ-5D Visual Analog Scale (EQ VAS). Change score models were used to investigate the relationship between HRQL and FEV1 and to calculate mean changes in HRQL per FEV1 change categories [decrease (≤ - 100 ml), no change, increase (≥ 100 ml)] after 3 years. Applying hierarchical linear models (HLM), we estimated the cross-sectional between-subject difference and the longitudinal within-subject change of HRQL as related to a FEV1 difference or change.
Results: We observed a statistically significant deterioration in SGRQ (total score + 1.3 units) after 3 years, which was completely driven by the activity component (+ 4 units). No significant change was found for the generic EQ VAS. Over the same period, 58% of patients experienced a decrease in FEV1, 28% were recorded as no change in FEV1, and 13% experienced an increase. The relationship between HRQL and FEV1 was found to be approximately linear with decrease in FEV1 being statistically significantly associated with a deterioration in SGRQ (+ 3.20 units). Increase in FEV1 was associated with improvements in SGRQ (- 3.81 units). The associations between change in FEV1 and the EQ VAS were similar. Results of the HLMs were consistent and highly statistically significant, indicating cross-sectional and longitudinal associations. The largest estimates were found for the association between FEV1 and the SGRQ activity domain.
Conclusions: Difference and change in FEV1 over time correlate with difference and change in disease-specific and generic HRQL. We conclude, that deterioration of HRQL should induce timely re-examination of physical status and lung function and possibly reassessment of therapeutic regimes.
Trial registration: NCT01245933. Date of registration: 18 November 2010.
Keywords: COPD; Cohort; Health status; Longitudinal; Patient reported outcome; Physical activity.