Impact of brainstem sleep mechanisms on pharyngeal motor control

Suppression of respiratory muscle activity in sleep, particularly evident i n the pharyngeal muscles, is pivotal to the pathogenesis of common sleep-re lated breathing disorders such as obstructive sleep apnea. Obstructive apne as are caused by sleep-related decrements in pharyngeal muscle activity tha t leads to snoring and airway obstruction in individuals with underlying st ructural narrowing of the upper airway. Since obstructive apneas occur excl usively during sleep, this disorder by definition is state-dependent and ul timately caused by the influences of brainstem sleep mechanisms on pharynge al motoneurons in individuals with compromised upper airway anatomy. This p aper reviews the central neuronal mechanisms by which sleep reduces the out put to the pharyngeal muscles and the neurotransmitters implicated in this alteration. The experimental approaches used to address this problem are al so mentioned and their relative advantages and disadvantages discussed. In particular, the information derived from reduced animal preparations is rev iewed and the need for studies in natural sleep is emphasised. Identifying the central neuronal mechanisms and neurotransmitters involved in sleep-rel ated suppression of pharyngeal muscle activity not only has important basic relevance to understanding state-dependent respiratory control, it also ha s immediate clinical relevance to understanding common sleep-related breath ing disorders at the central neuronal level. Determining these basic mechan isms also has immediate clinical relevance to understanding the pathogenesi s of airway occlusions, and guiding neuro-pharmacological approaches aimed at preventing the sleep-related decrements in pharyngeal muscle tone that a re ultimately the root cause of obstructive sleep apnea. (C) 2000 Elsevier Science B.V. All rights reserved.