Equine Upper Airway Obstruction Flashcards
where does most of the airway resistance come from in the equine airway
80-90% in upper airway
why are horses obligate nasal breathers
the soft palate is tightly opposed to the base of the larynx so there is no communication between the oropharynx and the nasopharynx
what are the cartilages that make up the equine larynx
- cricoid
- thyroid
- epiglottic
- paired arytenoid cartilages
label the cartilages of the equine larynx
what is each arytenoid cartilage composed of
two distinct processes
- corniculate process
- muscular process
what are the processes of the arytenoid cartilages
what are the structures of the larynx
the visible portions of the arytenoid cartilages are the corniculate processes
what is the function of the arytenoid cartilages during swallowing
adduct during swallowing and fully abduct at high intesity exercise
what are the intrinsic muscles of the larynx (6)
- cricoarytenoideus dorsalis
- cricothyroideus
- cricoarytenoideus lateralis
- vocalis
- ventricularis
- arytenoideus transversus
label the intrinsic muscles of the larynx
- cricoarytenoideus dorsalis (blue)
- cricothyroideus (red)
- cricoarytenoideus lateralis (orange)
- vocalis (yellow)
- ventricularis (green)
- arytenoideus transversus (purple)
what is the function of the cricoarytenoideus dorsalis muscle
abducts the arytenoids and tenses the vocal cords
what nerve innervates the cricoarytenoideus dorsalis muscle
recurrent laryngeal nerve
what is the hyoid apparatus composed of
- paired stylohyoid bones
- certahyoid bone
- thyrohyoid bones
- central basihyoid bone (which has lingual process)
label the structures of the hyoid apparatus
where does the epihyoid sit
at junction between the ceratohyoid and stylohyoid and is fused with the stylohyoid
what is the function of the hyoid apparatus
connects to the skull at the temporohyoid joint
this joint is where the paired largest bones in the hyoid apparatus (stylohyoid bones) articulate with the base of the skull
what are the functions of the muscles that attach to the hyoid apparatus
contraction of these muscles atler the shape and position of the apparatus which changes position and shape of the larynx and pharyx
what are the muscles of the hyoid apparatus
what are the extrinsic muscles of the larynx (8)
- hyoglossus
- genioglossus
- geniohyoideus
- muscles of tongue
- omohyoideus
- sternohyoideus
- sternothyroideus
- thyrohyoideus
what do the extrinsic muscles of the larynx attach to
onto the basihyoid bone, the lingual process of the basihyoid bone, the soft palate and pharynx
what is the function of the extrinsic muscles of the larynx
protracts (brings forward) and depresses the tongue as well as pulls the basihyoid bone rostrally which helps increase nasopharyngeal airway size and helps stabilize the walls of the nasopharynx
what are the extrinsic larynx muscles shown
hyoglossus (green)
genioglossus (pink)
geniohyoideus (yellow)
where do the omohyoideus, sternoihyoideus and sternothyroideus attach to
a group of muscles in the neck (accessory resp muscles) attach onto the caudal aspect of the thyroid cartilage, the basihyoid bone and the lingual process of the hyoid apparatus
what is the function of the omohyoideus, sternohyoideus and sternothyroideus muscles
contraction results in caudal traction of the hyoid apparatus and larynx –> dilation and stabilization of the nasopharynx
label the extrinsic laryngeal muscles
where does the thyroihyoideus muscle attach to
lateral surface of the thyroid cartilage and inserts on the thyrohyoid bone
what does contraction of the thyrohyoideus muscle result in
moves the hyoid apparatus caudally or the larynx rostrally and dorsally
helps maintain tight apposition between the soft palate and larynx –> maintains the soft palate ventral to the epiglottis
how do the muscles of the tongue and accessory respiratory muscles work together
help dilate and stabilze the nasopharynx
what are the clinical signs of upper resp obstructions
- noise occuring only during inspiration or expiration at exercise
- noise occuring during inspiration and expiration only at exercise
- noise during inspiration and expiration which is evident at rest
how does stride rate relate to respiratory rate
during gallop stride rate and resp rate are coupled
inspiration occurs when the limbs are off the ground (flight phase) and expiration occurs when the limbs strike out
what are the clinical signs of a horse in respiratory distress (6)
- loud abnormal resp noises
- nasal flaring
- reduced nasal airflow
- extended and low head position
- increased resp rate and effort
- cyanotic mucous membranes
what can severe cases of resp distress result in
dsyphagia, nasal reflux of food material and/or a cough
what are the steps in evaluating a patient with an abnormal respiratory noise during exercise and showing exercise intolerance
- patient history
- clinical exam
- resting upper airway endoscopy
- overground endoscopy
what are some questions you could ask when getting a concise patient history
- what is the intended use
- c/s: what are they? when do they occur? at rest or only during exercise?
- does the positioning of the head during work have any influence on the noise
- has the horse had upper resp surgery, or any prev trauma to the neck or upper resp tract
what are important steps in the clinical exam
- carefully auscultate the heart and lungs to rule out CVS disease and lower resp disease as a cause of poor performance
- palpate throat latch region and neck carefully to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
- airflow out of both nostrils and note the colour of nasal discharge
what can resting airway endoscopy diagnose
- subepiglottic cyst
- foreign body
- arytenoid chondritis
is this a normal upper airway on resting endoscopy
yes
what is recurrent laryngeal neuropathy (RLN)
inability to fully abduct the corniculate process of arytenoid cartilage most often the left side
results in inspiratory obstruction of the upper airway
what does progressive loss of large myleinated fibres of the recurrent laryngeal nerve cause
neurogenic atrophy of muscles of abduction especially the cricoarytenoideus dorsalis muscle (CAD)
what is shown here
atrophy of the left cricoarytenoideus dorsalis muscle (CAD)
how does recurrent laryngeal neuropathy (RLN) cause exercise intolerance (6)
- progressive loss of myelinated axons of the recurrent laryngeal nerve
- paralysis of CAD muscle
- inability to achieve max abduction of left arytenoid during exercise
- rima glottis progressively reduces in size
- hypoxemia, hypercarbia, metabolic acidosis
- early fatigue and poor performance
what causes recurrent laryngeal neuropathy (RLN) (5)
- most cases are idiopathic and involve large breed horses
- may be genetic
- trauma to recurrent laryngeal nerve (perivascular jugular vein injection of an irritant substance such as phenylbutazone)
- organophosphate toxicity
- hepatic encephalopathy (disfunction of both arytenoid cartilages)
how is recurrent laryngeal neuropathy (RLN) diagnosed with history
inspiratory whistling during exercise with variable degree of exercise intolerance (“roaring”)
what should you do in a clinical exam to assess recurrent laryngeal neuropathy (RLN)
- auscultate heart and lungs to rule out CVS
- palpate throat-latch region and neck to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
how is recurrent laryngeal neuropathy (RLN) graded during resting endoscopy
degree of abduction that can be achieved with stimulation of the larynx (swallowing)
four point system
what is grade 1 recurrent laryngeal neuropathy (RLN)
full and synchronous abduction of the arytenoid cartilages during resting upper airway endoscopy
what is grade 2 recurrent laryngeal neuropathy (RLN)
asynchronous movement of arytenoid cartilages but abduction is achieved with stiumlation of larynx
what is grade 3 recurrent laryngeal neuropathy (RLN)
asynchronous movement of arytenoid cartilages and full abduction cannot be achieved with stimulation of the larynx
ex. there is still movement in the left corniculate process of the arytenoid cartilage, but it is asynchronous with the right and full abduction cannot be achieved
what is grade 4 recurrent laryngeal neuropathy (RLN)
there is complete immobility of the affected arytenoid cartilage and vocal fold
can treatment decisions for recurrent laryngeal neuropathy (RLN) be made based soley on findings during resting endoscopy
ideally no
resting doesn’t replicate the function of the larynx during exercise and arytenoid function may change with the intro of exercise
overground is best way to assess upper airway dynamics and should be used in conjunction with resting endoscopy
how is recurrent laryngeal neuropathy (RLN) graded in overground endoscopy
four point
the degree of arytenoid abduction observed during resting endoscopy doesn’t correlate with the degree of arytenoid abduciton during exercise
what does grade A of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like
full abduction of the arytenoid cartilages during inspiration