Upper Resp. Tract Noise In Companion Animals Flashcards
what does athletic function in equines require
- low resistance
- high capacity
where does most airway resistance occur
80-90% is from upper airways
what occurs to airway resistance during exercise
increases by 80%
what occurs if diameter of airway reduces
if diameter reduces by 20% airway resistance doubles
what are the clinical signs of upper respiratory tract disease
- asymptomatic
- resp noise with or without exercise intolerance
- at gallop, stride rate and resp rate are coupled
- at trot, breathing and stride are independent
- dysphagia, nasal reflux of food material and/or cough
- resp. distress –> loud abnormal resp noise, nasal flaring, reduced nasal airflow, extended and low head position, increased resp rate and effort, severe cases may have cyanotic mucous membranes
what is the difference between stridor and stertor in dogs
- stridor –> harsh inspiratory noise at exercise, laryngeal paralysis, quiet at rest, profound dyspnoea at light exercise
- stertor –> snore at sleep and at exercise, brachycephalic breeds (fore-shortened noses and squashed pharynx, profound dyspnoea at sleep and exercise)
how is URT disease diagnostically evaluated
- history
- presenting complaint
- clinical signs (when do they occur –> rest or exercise)
- use or intended use
- effect of tack and head carriage
- prior surgery disease, or trauma of head and neck
how is respiratory disease investigated in horses
- full clinical exam (rule out lameness, cardiac disease, etc)
- lunge (both directions)
- exercise test (listen for upper resp noise and determine if its inspiratory, expiratory or both)
- rebreathing exam
what does a physical exam for URT disease entail (5)
- auscultate heart and lungs
- palpate jugular furrow and assess jugular fill (evidence of surgery, trauma, thrombosis of vein)
- palpate larynx (evidence of prior surgery, prominence of muscular process, laryngeal dysplasia)
- assess airflow from nostrils
- character of nasal discharge if any
how is a resting endoscopy performed and what does it evaluate (3)
unsedated
- nasal cavity, pharynx, larynx, trachea
- arytenoids –> function, thickness, mucosal lesions
- epiglottis –> position, thickness, ulceration, entrapping membrane
what does sedated endoscopy evaluate
- suepiglottic region –> may require topical anaesthesia
- guttural pouches
what is occuring here
larygneal paralysis
what are the differences in endoscopy with horses and dogs
horses: through the nasal cavity
dogs: through the oral cavity, soft palate is dorsal
what is occuring here
elongated soft palate
brachycephalics: stertor, dyspnea, death
what is the best diagnostic tool for diagnosing dynamic upper resp disorders
exercising upper airway endoscopy
approx 50% of horses presented for evaluation with normal resting endoscopy will have dynamic obstruction diagnosed on exercise exam and 19% to 56% of horses will have multiple abnormalities
what are the two methods of exercising upper airway endoscopy
- high speed treadmill
- overground endoscopy
what are the pros of highspeed treadmill exercise endoscopy (3)
- dynamic exam
- speed and incline can be altered
- training conditions are repeatable
what are the cons of highspeed treadmill exercise endoscopy (4)
- not ridden
- abnormal environment
- training required
- potentially dangerous
what are the pros of overground endoscopy
- dynamic exam
- more accurately recreates ridden conditions (environment, rider, tack, head carriage)
- inexpensive and more readily available
what are the cons of overground endoscopy
- same ridden conditions cannot be reproduced every time
what is recurrent laryngeal neuropathy
inspiratory disorder characterized by inability to fully abduct the corniculate process of an arytenoid cartilage (usually the left side)
what is recurrent laryngeal neuropathy caused by
neurogenic atrophy of muscles of abduction, especially the cricoarytenoideus dorsalis (CAD) muscle due to progressive loss of large myelinated fibres of recurrent laryngeal nerve (RLN) (damage/dysfunction)
what is occuring here
post mortem depiciting atrophy of the left CAD muscle
recurrent laryngeal neuropathy
what is the pathogenesis of recurrent laryngeal neuropathy caused by progressive loss of myelinated axons of RLN (5)
- paralysis of CAD muscle
- inability to achieve maximum abduction of left arytenoid during exercise
- rima glottis progressively reduces in size
- hypoxemia, hypercarbia and metabolic acidosis
- early fatigue and poor performance
what is the pathogenesis of recurrent laryngeal neuropathy
most cases are idiopathic and involve large-breed horses
genetic
other causes: trauma to nerve (perivascular injection), toxicity/organophosphates, hepatic encephalopathy (bilateral)
what is occuring here
bilateral laryngeal neuropathy due to hepatic encephalopathy
how is recurrent laryngeal neuropathy diagnosed (3)
- history: inspiratory roaring/whistling noise during exercise, variable degree of exercise intolerance, usually dependent on level of activity
- clinical examination: palpable laryngeal muscle atrophy (not reliable)
- resting and dynamic endoscopy
what is the grading systems for RLN in resting endoscopy
stage I: synchronous and full abduction of arytenoid cartilages
stage II: asynchronous movement, but full abduction is achieved with swallowing, nasal occlusion or use of resp stimulants
stage III: asynchronous movement, full abduction cannot be induced either by swallowing, nasal occlusion or use of resp stimulants
stage IV: complete immobility of arytenoid cartilage and vocal fold
what is the laryngeal grade for RLN in resting endoscopy
stage I
what is the laryngeal grade for RLN in resting endoscopy
stage II
what is the laryngeal grade for RLN in resting endoscopy
stage III
what is the laryngeal grade for RLN in resting endoscopy
stage IV
what are the grading systems for RLN using dynamic endoscopy
A: full abduction of arytenoid cartilages during inspiration
B: partial abduction of the left arytenoid cartilages between full abduction and the resting position
C: abduction less than resting position including collapse into the right half of the rima glottidis
how is RLN managed
based on presenting complaint (abnormal upper resp noise, poor performance, or both), age and use of horse, degree of arytenoid collapse during dynamic endoscopy
some horses can tolerate and work to capacity despite upper airway obstruction, esp when high speed is not expected
what are the treatment options for RLN
- prosthetic laryngoplasty (tie back)
- ventriculectomy or ventriculocordectomy
- reinnervation of the CAD muscle
- partial arytenoidectomy
what is prosthetic laryngoplasty
placement of suture prosthesis betwen cricoid cartilage and muscular process of affected arytenoid cartilage
mimics CAD muscle contraction –> allowing permanent abduction of corniculate process of the arytenoid cartilage
ideally –> sufficient arytenoid cartilage abduction to allow adeqate airflow during exercise, not allow entry of saliva, food or water into the laryngeal or tracheal lumen during swallowing
when would prosthetic laryngoplasty be appropriate
reserved for horses in which arytenoid collapse is confirmed with dynamic endoscopy and its having a negative impact on performance
how is the prognosis of prosthetic laryngoplasty
50-70% of racehorses will improve
75-90% of horses involved in non-racing will improve
what is occuring here
the right image shows a post op following tie back and left sided ventriculocordectomy
what is ventriculectomy
removal of mucosal lining of laryngeal ventricle (laryngeal saccule)
what is ventriculocordectomy (hobday)
more common than ventriculectomy
removal or ablation of vocal cord and ventricle
reduces inspiratory noise in horses but doesn’t return upper resp flow mechanics to baseline values
what is occuring here
unilateral (left sided) ventriculocordectomy performed via endoscopy using a diode laser
when is ventriculectomy and ventriculocordectomy appropriate (4)
- at same time as tie back in horses with grade 4 laryngeal movement where primary complaints are resp noise and exercise intolerance
- sport horses with grade 4 laryngeal movement where primary complaint is resp noise and exercise intolerance is not a concern
- racehorses with grade 3 laryngeal movement that don’t experience complete arytenoid collapse during high-speed exercise, but don’t experience vocal fold collapse identified during exercise videoendoscopy
- horses that have had a tide back and still experience vocal fold collapse
what is reinnervation of CAD muscle
first and second cervical nerve branches (C1/C2) which innervate the omohyoideus muscle are isolated and implanted into the CAD muscle to promote reinnervation
clinically evident approx 4-5 months post-surgery but can take up 12 months –> if no arytenoid abduction is observed 9 months after surgery, the chance of reinnervation is small
may not be suitable when immediate return to performance is necessary
when is reinnervation of CAD muscle done
younger horses and those with grade 3 laryngeal movements
80% success rate in a population of racehorses
which horses are not suitable for reinnervation of CAD muscle
horses that have had previous tie back aren’t candiates –> disruption of C1/C2 nerve branches during surgery or trauma and resultant fibrosis of CAD muscle
what is partial arytenoidectomy
removal of corniculate process and body of arytenoid cartilage via a laryngotomy –> leaving only the muscular process of the arytenoid cartilage intact
what is the goal of arytenoidectomy
improve airway geometry by increasing cross-sectional area of rima glottidis and prevent dynamic collapse of unsupported structures
what is a laryngotomy
surgical incision which provides access to interior of the larynx made ventrally at the level of larynx
when is a partial arytenoidectomy done
to treat RLN when there is congenital malformation of cartilages or when tie back has failed because of fracture of the laryngeal cartilages
what is the prognosis of partial arytenoidectomy
60-78% of horses return to racing
75% of non-racehorses return to their previous level of use
what do dogs with laryngeal paralysis present with
profound exercise induced dyspnoea
huge quality of life implications
what is treatment of laryngeal paralysis in dogs
tieback surgery to improve quality of life
but will never return to athletic function
what is dorsal displacement of soft palate
displacement of caudal free border of the soft palate dorsal to the epiglottis
what are the two types of dorsal displacement of the soft palate in dogs
- intermittent (most common)
- persistent
what is intermittent dorsal displacement of soft palate
dynamic condition
what is persistent dorsal displacement of soft palate
observed in resting horses
secondary to neurological damage –> ex. guttural pouch disease, neoplasia, peripheral neuropathies
causes major exercise intolerance and dysphagia
poor prognosis
what does dorsal displacement of the soft palate result in
expiratory airway obstruction
what is the prevalence of dorsal displacement of soft palate
10-20% of 2-3 year old thoroughbred and standardbred racehorses
sport horses exercised with head and neck in a flexed position (collected)
horses that have previously undergone a prosthetic laryngoplasty may be more susceptible to developing DDSP
what is the impact of collection on dorsal displacement of soft palate
- head and neck flexion
- alteration in upper airway dimensions
- increased airway resistance and negative inspiratory pressure
- instability of soft palate
- increased susceptibility to dorsal displacement of the soft palate
what does dorsal displacement of the soft palate lead to
- flow limiting expiratory obstruction
- increased tracheal expiratory pressure and impedance
- reduced minute ventilation
- hypoxia, hypercarbia, impaired athletic performance
what is the pathogenesis of dorsal displacement of soft palate
still unclear
50% of cases have concurrent lower airway disease
some horses will show signs of DDSP while unfit with resolution as their fitness increases
can occur with other disease (epiglottic entrapment)
research has identified several muscles or nerves where dysfunction could lead to DDSP
how is DDSP diagnosed
young performance horses
- character history: sudden impairement in performance, often at maximal exercise (towards the end of a race when fatigue may be a factor), gurgling, choking expiratory noise in approx 50% of cases, open mouth breathing
- endoscopy: resting and overground endoscopy
how is DDSP managed conservatively
- rest from exercise
- improve physical condition
- tack changes
- medical management of upper airway inflammation (systemic corticosteroids, systemic anti-inflammatory medications, topical throat sprays)
how is DDSP managed surgically
- tension, thermal and laser palatoplasty
- staphylectomy
- standard meyctomy
- minimally invasive myectomy
- laryngeal tie-forward
what is palatoplasty
reduced flaccidity of soft palate through fibrosis
tension palatoplasty (palatine mucosa and submucosa to level of palatine aponeurosis surgically removed, remaining mucosa sutured together)
thermal and laser palatoplasty: soft palate cauterized with heated steel rods or diode laser
what is laryngeal tie forward
replace action of thyrohyoideus muscles bilaterally –> larynx advances approx 4cm rostrally post-procedure as well dorsally –> increased soft palate-epiglottis contact
sutures placed between thyroid cartilage and basihyoid bone
bilateral sternothyroidectomy performed concurrently
what is the recent work of larygneal tie forward success
55-65%
what is dorsal displacement of soft palate
dorsal displacement of caudal free border of soft palate dorsal to epiglottis
what is occuring here
DDSP
