Pharyngeal musculature and obstructive sleep apnea syndromes

An analysis of the way the pharyngeal musculature modulates the caliber of the pharynx is important to better understand and treat obstructive sleep a pnea syndromes. The caliber of the pharynx at the soft palate depends on th e action of the tensor veli, the palatoglossus, the palatopharyngeus and th e uvula muscles. At the ligual level, the action of the genioglossus and th e geniohyoideus predominate. These different muscle groups contract in Go-o rdination before the diaphragm contracts. Their activity is diminished and disorganized during sleep. These muscles appears to have a histological com position adapted to short-duration intense contractions making them vulnera ble 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 o f an adaptive process. The degree of adaptation varies depending of the pha ryngeal level considered. Similar to their reflex stimulation, the response of these pharyngeal muscles to increased resistance is probably greatest a t the soft palate level. Greater solicitation of palatine muscles associate d with their greater vulnerability to fatigue could explain why obstruction is particularly important at this level. A study of the mechanical and his tological 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.