[Pharyngeal muscles and sleep obstructive apnea syndrome]

An analysis of the way the pharyngeal musculature modulates the caliber of the pharynx is important to better understand and treat obstructive sleep apnea syndromes. The caliber of the pharynx at the soft palate depends on the action of the tensor veli, the palatoglossus, the palatopharyngeus and the uvula muscles. At the ligual level, the action of the genioglossus and the geniohyoideus predominate. These different muscle groups contract in co-ordination before the diaphragm contracts. Their activity is diminished and disorganized during sleep. These muscles appears to have a histological composition adapted to short-duration intense contractions making them vulnerable to fatigue. In apneic patients, these muscles are solicited constantly. Muscular lesions related to overwork have been suggested. The histological composition of these muscles is modified in apneic patients compared with non-apneic subjects (increased number of type IIa fibres), the expression of an adaptive process. The degree of adaptation varies depending of the pharyngeal level considered. Similar to their reflex stimulation, the response of these pharyngeal muscles to increased resistance is probably greater at the soft palate level. Greater solicitation of palatine muscles associated with their greater vulnerability to fatigue could explain why obstruction is particularly important at this level. A study of the mechanical and histological properties of the pharyngeal musculature is required for a better understanding of the occlusive mechanisms of the upper airways and must be undertaken before initiating therapeutic stimulation of these muscles.