PO2-dependent changes in intrinsic and extrinsic tongue muscle activities in the rat.
BACKGROUND
Historically, respiratory-related research in sleep apnea has focused exclusively on the extrinsic tongue muscles (i.e., genioglossus, hyoglossus, and styloglossus). Until recently, the respiratory control and function of intrinsic tongue muscles (i.e., inferior and superior longitudinalis, transverses, and verticalis), which comprise the bulk of the tongue, were unknown.


OBJECTIVE
The current study sought to determine if extrinsic and intrinsic tongue muscles are coactivated in conditions of hypoxemia comparable to that experienced by adults with obstructive sleep apnea.


METHODS
Esophageal pressure and EMG activity of an extrinsic (hyoglossus) and an intrinsic (superior longitudinal) tongue muscle were studied in anesthetized, tracheotomized, spontaneously breathing rats. Average EMG activity was compared in a control gas condition (Pa(O2), 160 +/- 12 mm Hg) and in mild isocapnic hypoxia (Pa(O2), 69 +/- 7.2 mm Hg), with and without brief (3-breath) airway occlusions, pre- and postbilateral vagotomy.


RESULTS
(1) intrinsic and extrinsic tongue muscles are coactivated in mild hypoxia, (2) airway occlusion increased the activities of intrinsic retractor muscles in mild hypoxia, and (3) extrinsic retractor muscles have a steeper rate of rise of activity and an earlier burst onset relative to intrinsic retractor activities in mild hypoxia.


CONCLUSIONS
These findings support our working hypothesis that airway patency is maintained not simply by activation of extrinsic tongue muscles but by the coactivation of intrinsic and extrinsic protrudor and retractor muscles.
Bailey
E Fiona
EF
Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85721-0093, USA. ebailey@u.arizona.edu
Janssen
Patrick L
PL
Fregosi
Ralph F
RF
D000402:Airway Obstruction / Q000209:etiology / Q000503:physiopathology*; D000818:Animals; D004195:Disease Models, Animal; D004576:Electromyography; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism*; D011659:Pulmonary Gas Exchange; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration; D012680:Sensitivity and Specificity; D014059:Tongue / Q000294:innervation / Q000502:physiology*; D014139:Tracheostomy; D014628:Vagotomy
D010100:Oxygen