The overlap syndrome of obstructive sleep apnoea (OSA) and
chronic obstructive pulmonary disease (
COPD), in addition to
obesity hypoventilation syndrome, represents growing health concerns, owing to the worldwide
COPD and
obesity epidemics and related co-morbidities. These disorders constitute the end points of a spectrum with distinct yet interrelated mechanisms that lead to a considerable health burden. The coexistence OSA and
COPD seems to occur by chance, but the combination can contribute to worsened symptoms and
oxygen desaturation at night, leading to disrupted sleep architecture and decreased sleep quality. Alveolar
hypoventilation, ventilation-perfusion mismatch and intermittent hypercapnic events resulting from
apneas and hypopneas contribute to the final clinical picture, which is quite different from the "usual"
COPD.
Obesity hypoventilation has emerged as a relatively common cause of chronic
hypercapnic respiratory failure. Its pathophysiology results from complex interactions, among which are respiratory mechanics, ventilatory control,
sleep-disordered breathing and neurohormonal disturbances, such as
leptin resistance, each of which contributes to varying degrees in individual patients to the development of
obesity hypoventilation. This respiratory embarrassment takes place when compensatory mechanisms like increased drive cannot be maintained or become overwhelmed. Although a unifying concept for the pathogenesis of both disorders is lacking, it seems that these patients are in a vicious cycle. This review outlines the major pathophysiological mechanisms believed to contribute to the development of these specific clinical entities. Knowledge of shared mechanisms in the overlap syndrome and
obesity hypoventilation may help to identify these patients and guide
therapy.