Sleep obstructive apnea syndrome (SOAS) is a life-threatening respiratory disorder. Its combination with COPD further deteriorates respiratory distress and accelerates the development of pulmonary hypertension (crossover syndrome). Systemic inflammation with concomitant oxidative stress in patients with SOAS and COPD suggests their influence on the development of circulatory disorders. Night-time cyclic hypoxia in patients with SOAS triggers systemic inflammation, oxidative stress, and atherogenesis which accounts for the frequent complications more severe in combination of SOAS and COPD than in either of these diseases. Intermittent hypoxia in patients with SOAS is associated with hypoventilation resulting from COPD, deteriorates clinical conditions of the patients, and requires the choice of specific methods of respiratory support.