Tongue protrusion strength and fatiguability: Relationship to apnoea/hypopnoea index and age

The sleep apnoea/hypopnoea syndrome (SAHS) is characterized by retroglossal or retropalatal narrowing. The site of obstruction, and the fact that nega tive pressure in the upper ail way increases retroglossal airway size, sugg ests that tongue muscles may play a role in the maintenance of upper airway patency. We therefore hypothesized that tongue protrusion strength and fat iguability may be predictors of apnoea/hypopnoea index, vary with age and m ay be different in SAHS patients and normal subjects. Maximal strength (F-m ax) and fatiguability (measured as the total time subjects were able to mai ntain 50% F-max on three consecutive occasions separated by 30 s) were asse ssed using a force transducer in 98 consecutive apnoeic/hypopnoeic male pat ients referred to our laboratory for sleep studies apnoea/hypopnoea index ( AHI) range 3-130/h, age range 30-74 yl. F-max and fatiguability were also c ompared in 15 male SAHS patients (mean AHI 20/h) and 15 nonsnoring male sub jects matched for age, body mass index and fat free mass. A further 26 SAHS patients had tongue protrusion strength/ fatiguability measured before, du ring and after a night's sleep. Log AHI was only weakly correlated with F-m ax (r = - 0.21; P = 0.03) and age (r = 0.23; P = 0.025), but not to fatigua bility (P > 0.05). Comparison between SAHS and nonsnoring subjects did not demonstrate significant differences in F-max (P = 0.1) or fatiguability (P = 0.1). There was no evidence of a change in muscle strength (P > 0.05) or fatigue (P > 0.05) during the course of a night's sleep. We conclude that t ongue protrusion strength and fatiguability are unlikely to be important fa ctors in the pathogenesis of SAHS.