ABSTRACT
Sleep-related breathing disorders occur due to the effects of sleep on the central nervous respiratory control system and/or on upper airway (UA) patency. The occurrence of partial or complete UA obstruction during sleep characterizes the obstructive sleep apnea (OSA)/hypopnea syndrome. Breathing (respiration), which is mainly under a behavioral or voluntary control system during awakening, is essentially under a metabolic or automated control system during sleep. The contribution of the thoracic cage to the overall respiration remains the same during wakefulness and nonrapid eye movement (NREM) sleep. Considering the importance of the metabolic regulation in the control of respiration during sleep, one can easily speculate that any change in the ventilatory response to hypoxic or hypercapnic stimuli will increase the magnitude of nocturnal hypoventilation episodes. UA are usually patent throughout the respiratory cycle and they behave in a manner similar to that of a Starling resistance model where a collapsible segment (pharynx) is located between two noncollapsible segments.
