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 negative pressure in the upper ail way increases retroglossal airway size, suggests that tongue muscles may play a role in the maintenance of upper airway patency. We therefore hypothesized that tongue protrusion strength and fatiguability may be predictors of apnoea/hypopnoea index, vary with age and may be different in SAHS patients and normal subjects. Maximal strength (F-max) and fatiguability (measured as the total time subjects were able to maintain 50% F-max on three consecutive occasions separated by 30 s) were assessed using a force transducer in 98 consecutive apnoeic/hypopnoeic male patients 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 compared in 15 male SAHS patients (mean AHI 20/h) and 15 nonsnoring male subjects matched for age, body mass index and fat free mass. A further 26 SAHS patients had tongue protrusion strength/ fatiguability measured before, during and after a night's sleep. Log AHI was only weakly correlated with F-max (r = - 0.21; P = 0.03) and age (r = 0.23; P = 0.025), but not to fatiguability (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 tongue protrusion strength and fatiguability are unlikely to be important factors in the pathogenesis of SAHS.