Describe the physiology of the gag reflex
- Gag reflex = prevents foreign material entering trachea, pharynx, or larynx
- Brisk brief elevation of soft palate with bilateral contraction of constrictor muscles of pharynx resulting in ejection of unwanted, irritating, or toxic material
- After intraoral stimulation afferent fibers of trigeminal, glossopharyngeal, and vagus nerves pass to medulla oblongata
- Efferent impulses then cause spasmodic and uncoordinated muscle movements (gagging). The vomit, salivating, and cardiac centers in the medulla oblongata can also be stimulated due to their close proximity
- Neural pathways from the gag center to cerebral cortex allow the reflex to be modified by higher centres, illustrating why gagging may be elicited by nontactile sensations such as visual or olfactory stimuli.
- Gagging implies pharyngeal or retropharyngeal dysphagia and describes a patient that is trying to swallow in the presence of a dysfunctional pharyngeal phase of swallowing process.
Describe the motion of retching
- Retching = involuntary and futile attempt at vomiting associated with nausea.
- The direction of spasmodic and uncoordinated peristalsis is reversed and air is forced over the closed glottis producing a retching sound.
- Occurs post-swallowing and suggest oesophageal dysmotility
- Ongoing retching culminates the act of vomiting
Describe the oral pharyngeal and oesophageal phase of deglutition
- The pharyngeal phase involves movement of the bolus from the pharynx to the oesophagus.
- The sequential contractions are initiated b stimulation of sensory receptors through touch, pressure, and similar action of food on the tongue, facial pillars, soft palate, uvula, epiglottis, pharyngeal wall, and/or junction between the pharynx and oesophagus.
- The corresponding nerve fibres belong to the maxillary branch of cranial nerves V and IX to the cranial laryngeal nerve.
- The afferent nerves V and IX and to the cranial laryngeal nerve. The afferent pathways carry information from peripheral receptors to the brainstem and evoke contractions of buccal, tongue, pharyngeal, and esophageal muscles, propelling the food bolus aboraly.
List differentials for gagging originating in nasal sinus and the diagnostic test
- Cleft palate
oropharyngeal examination
- Nasal parasites (Capillaria, Pneumonyssoides spp.)
- Nasal foreign body
rostral and retrograde exam of nasal passage
rhinoscopy
- Nasal tumors
’as above’ + CT scan/biopsy
List differentials (and their tests) that cause gagging originating from morphological abnormalities of the pharynx.
Neoplasia
Pharyngitis
Pharyngeal abscess
- oropharyngeal exam
- CT/MRI scan
- FNA or core biopsy and histopathology
Foreign body
- Oropharyngeal exam, fistulogram, CT/MRI scan
Tonsillitis
- Tonsillectomy
Elongated soft palate
- Oropharyngeal exam
Nasopharyngeal polyps
- Oropharyngeal and nasopharyngeal examination
Pharyngeal mucocele
- Oropharyngeal examination
- FNA cytology
Stylohyoid Disarticulation
- Oropharyngeal examination
- pharyngeal radiography or CT scan
Cricopharyngeal bar
- videofluoroscopy, -manometry
List differentials (and their tests) that cause gagging originating from functional abnormalities of the pharynx.
Cricopharyngeal achalasia
- videofluoroscopy,
-manometry
Crichopharyngeal dyssynchrony
- Videofluorscopy
- manometry
List neuromuscular differntial Dx’s for gagging and their diagnostic tests
inflammatory
neuromuscular exam
EMG
Muscle biopsy
Degenerative/Idiopathic
‘as above’ + brain imaging
Neoplastic
Neuro exam
CT/MRI scan of brainstem
Infectious (rabies, pseudorabies)
history of exposure
vaccination history
Clinical course
Histopathology
Hypocalcemia
Serum (ionised) calcium concentration
List URT morphological differntial Dx’s for gagging and their diagnostic tests
Foreign body
Pharyngeal/laryngeal exam
Radiography
CT/MRI
Endoscopy
Neoplasia
‘as above’ + cytology, histopathology
Tracheal collapse
Radiography
Fluoroscopy
Endoscopy
List URT functional differential Dx’s for gagging and their diagnostic tests
Laryngeal paralysis
pharyngeal
laryngeal examination
Laryngitis
pharyngeal
laryngeal examination
Tracheobronchitis
radiography
transtracheal aspiration cytology/culture, bronschoscopy
List LRT functional differential Dxs and their tests for gagging
Feline chronic bronchial disease
Radiography
Bronchoalveolar lavage
Canine tracheobronchitis
History
Physical examination
Tracheal cytology
Fungal pneumonitis
history
radiogrpahy
tracheal and bronchial cytology
fungal antigen test
List esophageal functional differential Dxs and their tests for gagging
Esophagitis
history
endoscopy
cytology/histopathology
Esophageal motility disorder
”as above” + Acb receptor Ab titer
Edrophonium response test
EMG
Thyroid profile
Resting serum cortisol concentration/ACTH stimulation
muscle biopsy
List esophageal morphological differential Dxs and their tests for gagging
Stricture/stenosis
Stenosis
History
(contrast) radiograph +/- fluoroscopy
Endoscopy
