Exertional Desaturation as a Predictor of Rapid Lung Function Decline in COPD

Background: To date, no clinical parameter has been associated with the decline in lung function other than emphysema severity in COPD. Objectives: The main purpose of this study was to explore whether the rate of lung function decline differs between COPD patients with and without exertional desaturation. Methods: A total of 224 subjects were selected from the Korean Obstructive Lung Disease cohort. Exertional desaturation was assessed using the 6-min walk test (6MWT), and defined as a post-exercise oxygen saturation (SpO₂) of <90% or a ≥4% decrease. The cohort was divided into desaturator (n = 47) and non-desaturator (n = 177) groups. Results: There was a significant difference between the desaturator and non-desaturator groups in terms of the change in pre-bronchodilator forced expiratory volume in 1 s (FEV₁) over a 3-year period of follow-up (p = 0.006). The mean rate of decline in FEV₁ was greater in the desaturator group (33.8 ml/year) than in the non-desaturator group (11.6 ml/year). A statistically significant difference was also observed between the two groups in terms of the change in the St. George's Respiratory Questionnaire (SGRQ) total score over 3 years (p = 0.001). Conclusions: This study suggests, for the first time, that exertional desaturation may be a predictor of rapid decline in lung function in patients with COPD. The 6MWT may be a useful test to predict a rapid lung function decline in COPD.