[Coexistence of obstructive sleep apnea syndrome and chronic obstructive pulmonary disease]

Both obstructive sleep apnea (OSA) syndrome and chronic obstructive pulmonary disease (COPD) may lead to chronic alveolar hypoventilation. The coexistence of OSA syndrome and COPD has been named the overlap syndrome. The aim of the study was to elucidate the relationship between the severity of COPD and the occurrence of chronic alveolar hypoventilation in patients with OSA syndrome.

The material of the study consisted of 64 obese (BMI 40 ± 5.5 kg/m(2)) patients with OSA syndrome (AHI 〉15, mean 52 ± 23) and coexisting COPD (FEV1/FVC 〈 70%). The results of polysomnographic, spirometric and arterial blood gases studies have been evaluated.

Chronic alveolar hypoventilation has been found in 67% of the patients: in 60.5% of patients in the spirometric stage II, in 85% of patients in the stage III and in all the patients in the stage IV of COPD. In the patients with chronic alveolar hypoventilation as compared with the remaining patiens there were: lower FVC (2.7 ± 0.8 L v. 3.6 ± 0.9 L; p 〈 0.001), FEV(1) (1.7 ± 0.6 L v. 2.2 ± 0.5 L; p 〈 0.001) and mean SaO(2) during obstructive sleep apneas and hypopneas (75 ± 10% v. 84 ± 5%; p 〈 0.001).

Chronic alveolar hypoventilation occurs in most of the obese patients with moderate and severe OSA syndrome and coexisting COPD, including most of the patients with moderately impaired ventilatory function. The occurrence of chronic alveolar hypoventilation in the course of the overlap syndrome is related to the restrictive ventilatory pattern and the lower mean and minimal SaO(2) during obstructive sleep apneas and hypopneas.