Overlap syndrome is the association of obstructive sleep apnea (OSA) with chronic obstructive pulmonary disorder and with other chronic respiratory diseases. Patients with overlap syndrome have a worse prognosis compared with chronic obstructive pulmonary disorder or OSA alone. Additionally, patients with combined chronic obstructive pulmonary disorder and OSA are more likely to develop pulmonary hypertension and right heart failure much earlier than those without overlap.

To assess the occurrence of pulmonary hypertension (PH) in newly diagnosed OSA-chronic obstructive pulmonary disorder overlap syndrome patients attending a tertiary care centre.

This cross-sectional study was conducted at Department of Pulmonary Medicine, Government Medical College, Kozhikode, Kerala, South India, among patients with OSA above 40 years of age who were proactively evaluated to pick out those with undiagnosed overlap. A period of 6 months after getting ethical clearance from June 2018 was selected as the study period. Among patients with symptoms suggestive of OSA above 40 years of age who gave the informed consent were enrolled after screening with Standard Sleep questionnaires (Berlin questionnaire, STOP BANG and Epworth Sleepiness Scale). Enrolled patients underwent routine spirometry and sleep study using the standard Level 1 overnight polysomnography (Level1 OPSG). Patients were classified in to two groups as OSA patients (group I), having an apnea hypopnea index (AHI) > 5/hr alone and the second group as those OSA patients (group II), with an obstructive spirometry pattern who were the overlap group. Arterial blood gas analysis (a sample of radial arterial blood was drawn with the patient awake and supine, and was analyzed for pH, PaCO2 and PaO2) and echocardiography (ECHO) of the two groups were compared as a non-invasive method to assess pulmonary artery hypertension and results were analyzed in a systematic manner.

Among the 84 patients enrolled, 16.7% had overlap syndrome and the rest had OSA alone. Statistically significant higher mean weight and BMI for those with overlap syndrome compared to the OSA group were observed. Mean FVC (forced vital capacity), FEV1 (forced expiratory volume 1 s), and FEV1/FVC were lower in those with overlap syndrome compared to OSA group. The mean values of ABG parameters revealed higher PaCO2 and lower PaO2 among the group with overlap syndrome which were statistically significant. However, there was no significant difference in resting room air SaO2 value between the two groups. The mean values of sleep duration and efficiency were significantly lower in those with overlap syndrome with a p value < 0.001. The mean value of arousal and REM (rapid eye movement) sleep percentage were significantly higher among those with overlap syndrome (p < 0.001). Mean value of NREM (non-rapid eye movement) sleep percentage was lower among the group with overlap syndrome compared with the OSA group, and this difference was statistically significant. The mean AHI value of the overlap syndrome group was 39.79 ± 7.54 and this was significantly higher than the OSA group (p < 0.004). Among the 14 patients who had ECHO evidence of pulmonary hypertension, 9 (64.3%) belonged to the overlap group which shows that they are a highly vulnerable group for developing pulmonary hypertension (PH) and requires early detection and more rigorous treatment.

This study confirms that OSA patients with modest daytime level of hypoxemia and mild-moderate chronic airflow limitation have a high prevalence of PH. Chronic airway obstruction may be asymptomatic in some subjects and this stresses the necessity of pulmonary function test in OSA.