title: Relationship between upper airway and inspiratory pump muscle force in obstructive sleep apnea.
abstract: BACKGROUND
  Upper airway (UA) patency during inspiration is determined by the balance between dilating forces generated by UA dilator muscle activity and collapsing forces related to the decreased intraluminal pressure that accompanies flow generated by inspiratory muscle activity. It is possible that the relative strengths of UA dilator and inspiratory pump muscles could be an important determinant of the susceptibility to UA collapse during sleep (ie, obstructive sleep apnea [OSA]).
  
  
  METHODS
  Measurements of tongue protrusion (TP) force and maximum inspiratory pressure (Pimax) were obtained in 94 patients admitted for overnight polysomnography for suspected OSA, quantified by apnea-hypopnea index (AHI).
  
  
  RESULTS
  There was a direct linear relationship between TP force and Pimax (r(2) = 0.37, p < 0.001). A high ratio of TP force to Pimax (greater than group 90th percentile, 0.027 kg/cm H(2)O) appeared to protect against OSA, as moderate-to-severe OSA (AHI > 20/h) was not observed in any individual with a ratio above this threshold. AHI was not linearly related to TP force, Pimax, or the ratio of TP force to Pimax.
  
  
  CONCLUSIONS
  UA muscle strength is linearly related to inspiratory pump muscle strength. The ratio of UA muscle strength (TP force) and inspiratory pump muscle strength (Pimax) was not different between individuals with and without OSA; however, a high wakeful ratio of TP force to Pimax appears to be associated with a reduced propensity to moderate-to-severe OSA.
authors.affiliation: West Australian Sleep Disorders Research Institute, Department of Pulmonary Physiology, Sir Charles Gairdner Hospital, Nedlands, Western Australia 6009, Australia.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Shepherd
authors.forename: Cathryn M
authors.initials: CM
authors.lastname: Jensen
authors.forename: Kathleen J
authors.initials: KJ
authors.lastname: Maddison
authors.forename: David R
authors.initials: DR
authors.lastname: Hillman
authors.forename: Peter R
authors.initials: PR
authors.lastname: Eastwood
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D009765:Obesity / Q000503:physiopathology; D017286:Polysomnography; D012016:Reference Values; D012115:Residual Volume / Q000502:physiology; D012132:Respiratory Muscles / Q000503:physiopathology*; D012307:Risk Factors; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D014059:Tongue / Q000503:physiopathology*; D014851:Wakefulness / Q000502:physiology