Nocturnal Oxygen Desaturation Index is Inversely Correlated with Airflow Limitation in Patients with Chronic Obstructive Pulmonary Disease

The concurrent diagnosis of chronic obstructive pulmonary disease (COPD) and sleep apnoea–hypopnoea syndrome (SAHS) (overlap syndrome), can contribute to worsening respiratory symptoms, but whether the severity of COPD is associated with co-morbid SAHS is unknown. We investigated whether the severity of COPD is associated with the complication of SAHS by examination of nocturnal oximetry as an alternative to polysomnography. Patients with COPD concurrently completed nocturnal oximetry, pulmonary function tests, a COPD assessment test, an Epworth sleepiness scale and a hospital anxiety and depression scale to evaluate the severity of COPD and possible concurrent presence of SAHS. We retrospectively analysed the data to assess correlation between the oxygen desaturation index (ODI) and each clinical variables and evaluated the predictors of ODI ≥ 15. This study included 103 patients (91 males, 88%) with a mean age of 72 ± 8 years and body mass index of 22 ± 3 kg/m². ODI was positively correlated with FEV₁, FEV₁/FVC and FEV₁% predicted, which meant that ODI was inversely correlated with airflow limitation. Univariate logistic regression analysis revealed that FEV₁% predicted and FEV₁/FVC were predictors of ODI ≥ 15. ODI is inversely correlated with airflow limitation and milder COPD patients may have co-morbid SAHS.