title: Effects of hypoglossal nerve block and electrical stimulation of the thyrohyoideus muscles on position of the larynx and hyoid apparatus in healthy horses.
abstract: OBJECTIVE
  To determine the effects of hypoglossal nerve block and electrical stimulation of the thyrohyoideus muscles on position of the larynx and hyoid apparatus in resting horses.
  
  
  METHODS
  16 healthy horses that underwent hypoglossal nerve block and 5 healthy horses that underwent electrical stimulation of the thyrohyoideus muscles.
  
  
  METHODS
  Horses underwent bilateral hypoglossal nerve block or electrical stimulation of the thyrohyoideus muscles. Positions of the basihyoid bone, ossified part of the thyroid cartilage, and articulations of the thyrohyoid bones and thyroid cartilage were determined in radiographic images obtained before and after performance of hypoglossal nerve blocks or during thyrohyoideus muscle stimulation. Radiographic images were obtained with the heads of horses in neutral (thyrohyoideus muscle stimulation) or neutral and extended (hypoglossal nerve block) positions. Radiographic images of horses obtained after performance of hypoglossal nerve blocks were also evaluated to detect dorsal displacement of the soft palate.
  
  
  RESULTS
  Hypoglossal nerve blocks did not induce significant changes in the positions of evaluated anatomic sites in radiographic images obtained in neutral or extended head positions. Hypoglossal nerve block did not induce dorsal displacement of the soft palate in horses at rest. Bilateral thyrohyoideus muscle stimulation induced significant dorsal movement (mean ± SD change in position, 18.7 ± 6.8 mm) of the ossified part of the thyroid cartilage; rostral movement of evaluated anatomic structures was small and not significant after thyrohyoideus muscle stimulation.
  
  
  CONCLUSIONS
  Bilateral electrical stimulation of the thyrohyoideus muscles in horses in this study induced dorsal laryngeal movement.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Alanna J
authors.initials: AJ
authors.lastname: Zantingh
authors.forename: Norm G
authors.initials: NG
authors.lastname: Ducharme
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Mitchell
authors.forename: Jonathan
authors.initials: J
authors.lastname: Cheetham
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006736:Horses / Q000502:physiology*; D006928:Hyoid Bone / Q000502:physiology*; D007002:Hypoglossal Nerve / Q000187:drug effects*; D007830:Larynx / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal; D009407:Nerve Block / Q000662:veterinary*