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Dynamic respiratory tract Flashcards

1
Q

How much air does a galloping horse require?

A

1500 L/min of air

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2
Q

Which are the non-rigid parts of the upper airway?

A

nostrils, nasopharynx and larynx

active muscular effort is required to resist collapse and maintain an adequate, functional airway.

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3
Q

Regions of the upper airway with the smallest diameter (and so largest resistance to airflow)

A

Nostrils

Larynx

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4
Q

When during the stride does inspiration occur?

A

Inspiration occurs at the canter or gallop as the leading leg is lifted off the ground

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5
Q

Very common URT disorders

A

Recurrent laryngeal neuropathy,
soft palate disorders,
medial deviation of the ary-epiglottic folds,
vocal fold collapse,
false nostril flutter (high blowing)

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6
Q

Fairly frequent URT disorders

A

Epiglottic entrapment,
arytenoid chondritis,
laryngeal dysplasia,
nasopharyngeal collapse.

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7
Q

Rare URT disorders

A

Epiglottic retroflexion,
sub-epiglottic cysts,
epiglottitis,
tracheal collapse,
bilateral laryngeal paralysis,
ventro-medial collapse of the corniculate process of arytenoid,
alar fold collapse (nostrils)

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8
Q

High blowing

A

false nostril flutter

incidence = v. common

In normal horses during exercise, expiratory noises are louder than the inspiratory noises.

In ‘high blowers’, even louder and more vibrant expiratory noises are made, usually at the start of exercise.

Often disappears as they get faster

During high blowing the true nostril can clearly be seen to vibrate in most animals.

These noises may be voluntary in some animals, e.g. with fear, aggression or excitement and may resemble snorting (forceful nasal expiratory sounds). They are not clinically significant.

No obstruction caused

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9
Q

Nasal paralysis

A

Facial nn VII damage

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10
Q

Alar fold collapse

A

Rare

Fleshy fold lies in the rostral nasal cavity and is attached rostrally to the medial aspect of the false nostril and caudally to the ventral nasal concha.

It can collapse into, and obstruct the nasal cavity at exercise, causing loud vibrating noises – thought to create mild to moderate expiratory obstruction.

This fold may be surgically removed in the standing horse using a vessel sealer, or with open surgery.

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11
Q

Nasopharynx anatomy

A

Muscular tube
○ Connects nasal/oral cavities -> larynx/oesophagus

Horse has intra-narial larynx

Soft palate divides nasopharynx from oropharynx

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12
Q

Soft palate anatomy

A

Muscular structure separating oral cavity and oropharynx from nasopharynx

Dorsal aspect forms floor of the nasopharynx

Should lie under the epiglottis and fit snugly around it

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13
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability.

A

Occurs in racehorses at maximal exertion

Palate becomes displaced DORSAL to the epiglottis = PALATAL INSTABILITY – can no longer visualise epiglottic cartilage

Only really affects horses at v. fast exercise e.g. racehorses, eventers.

Palatal instability (dorsal ‘billowing’ of soft palate) usually precedes true DDSP.

If the soft palate displaces dorsally to epiglottis -> airflow obstruction (mainly expiratory).

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14
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- incidence

A

Thought to be most common dynamic respiratory disorder (up to 20% prevalence).

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15
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- clinical signs

A

production of loud abnormal gurgling expiratory and inspiratory noises (but up to 20% of DDSP horses are ‘silent’ displacers) + reduced exercise performance.

Often horses reported to ‘stop suddenly’ during racing, particularly at end of race.

Expiratory obstruction

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16
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- Aetiology

A

Unknown, many proposed causes (and treatments):

Dysfunction of thyro-hyoid muscle
- tie forward

Primary dysfunction of intrinsic palate muscles
- thermal cautery of oral aspect of palate to fibrose

Excessive caudal retraction of larynx
- myectomy of strap muscles
- tie forward
- tongue tie

Damage to pharyngeal branch of vagus nerve
- rest, treat concurrent inflammation etc.

Hypoxaemia or exhaustion
- conservative

Epiglottic hypoplasia
- augmentation with teflon

Excessive tissue or flaccidity
- staphylectomy

Prediposing lesion

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17
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- diagnosis

A

history of gurgling noise + poor performance, but this method -> 35% misdiagnosis rate

Only way to definitively dx = exercising endoscopy.

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18
Q

Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- treatment

A

The large number of surgical procedures currently used to treat DDSP underlines the fact that none are particularly effective.

Conservative: 33–100 % ‘success’ rate
§ Tongue tie
§ Dropped/figure 8/Australian noseband
§ Medical therapy (topical/systemic anti- inflammatories)
§ Rest ‘immature’ horses
§ Increase fitness level

Surgery: 50–80 % ‘success’ rate
§ Tie-forward (thyro-hyoid prosthesis) – 80% success rate
§ Palatoplasty (surgical, cautery or laser)
§ Staphylectomy
§ Epiglottic augmentation
§ Sternothyroid tenectomy or sternothyrohyoid myectomy

Combinations of any of the above!

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19
Q

Permanent DDSP

A

Rare

Apparent at rest

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20
Q

Nasopharyngeal collapse - incidence

A

Uncommon

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21
Q

Nasopharyngeal collapse - aetiology

A

often unknown - thought to be related to neuromuscular dysfunction of the nasopharynx.

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22
Q

Nasopharyngeal collapse - clinical signs

A

respiratory noise and obstruction in racehorses and overweight cobs/ponies

Classified as lateral, circumferential or dorsoventral depending on which walls are collapsing during inspiration.

In more severely affected horses, usually associated with abnormal respiratory noises which may vary from a low-intensity, low pitched ‘grunts’ to a vibrant inspiratory and/or expiratory ‘snore’ or ‘gurgle’.

Often associated with flexion of the head and neck, and affected horses may appear normal with the head and neck extended during exercise

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23
Q

Nasopharyngeal collapse - diagnosis

A

Need exercising endoscopy

24
Q

Disorders of the larynx

A

Many disorders may be visible during resting endoscopy

Almost ALL laryngeal disorders will cause dynamic obstruction at exercise

25
Function of the larynx
Open airway wide when exercising ○ Arytenoid cartilages move laterally and dorsally = ABDUCTION ○ Muscle pulling the arytenoids outwards = cricoarytenoideus dorsalis (CAD) Close and protect the airway when swallowing ○ Arytenoid cartilages move medially and ventrally = ADDUCTION ○ Epiglottis then lifts up, food passes over larynx into oesoph. NB: MAXIMAL arytenoid abduction always occurs immediately after swallowing
26
Epiglottic entrapment (EE) + Subepiglottic cysts
usually apparent at rest
27
Epiglottic retroflexion
Rarely seen as dynamic disorder during high speed treadmill endoscopy -> epiglottis ‘inhaled’ caudally into rima glottidis.
28
Clinical signs of epiglottic entrapment
abnormal resp noise (‘gulping’ during inspiration’) +/- poor performance. Possibly due to dysfunction of hypoglossal nerve or hyoepiglotticus/geniohyoid muscles
29
Treatment of eppiglottic retroflexion
surgery = epiglottopexy ties epiglottis to thyroid cartilage
30
Recurrent laryngeal neuropathy (RLN)
aka: idiopathic laryngeal hemiplegia (LH), idiopathic laryngeal hemiparesis, "roaring", “whistling”, laryngeal paralysis. Incidence -COMMON This is the most important URT airway obstruction of the larger equine breeds, especially TB's, TB crosses, Warmbloods and draught horses. Conversely, it is very rare in ponies. Terminology of this condition is confusing, but Recurrent laryngeal neuropathy (RLN) is correct -> refers to both partial and total unilateral laryngeal dysfunction.
31
Recurrent laryngeal neuropathy (RLN) - aetiology
vast majority of cases = idiopathic degenerative neuropathy of the left recurrent laryngeal nerve, -> innervates intrinsic laryngeal mm’s. Some genetic component now proven. Adductor dysfunction -> no clinical signs, but ABDUCTOR dysfunction i.e. the cricoarytenoideus dorsalis (CAD) muscle -> inability to fully open larynx during exercise. Occasionally laryngeal dysfunction, (left or right sided) can have a different aeitiology e.g. guttural pouch mycosis or damage to the recurrent laryngeal nerves at some other site, e.g. in the cervical area, due to a perivascular irritant injection, cervical or intra-thoracic tumour, post oesophageal or thyroid surgery etc.
32
Recurrent laryngeal neuropathy (RLN) - idiopathic form
most common form Only affects tall horses (>15.2 hh) Distal axonopathy of left recurrent laryngeal nerve Left side affected c.f. right because left recurrent laryngeal nerve is longer than right Longest nerve in the body Can occur or worsen at any age
33
Recurrent laryngeal neuropathy (RLN) - non-idiopathic form
RLN occasionally caused by other insults to nerve Right or left sided (or bilateral) Perivascular injection of irritant material (neck) Traumatic damage to nerve (neck or cr. thorax) Damaged within guttural pouch (gp mycosis) Systemic disease e.g. severe liver disease, lead poisoning
34
Recurrent laryngeal neuropathy (RLN) - pathophysiology
Left CAD muscle undergoes atrophy Left arytenoid cartilage can no longer fully abduct – sucked in towards midline during inspiration Left vocal fold may also prolapse Collapsing arytenoid/vocal fold § Turbulent airflow abnormal respiratory noise at exercise § INSPIRATORY high pitched whistle in mild cases § INSPIRATORY loud ‘roar’ in severely affected cases § Obstruction to airflow exercise intolerance
35
Recurrent laryngeal neuropathy (RLN) - clinical signs
Abnormal inspiratory noise (‘whistle’ or ‘roar’) at exercise +/- poor performance.
36
Recurrent laryngeal neuropathy (RLN) - diagnosis
History Palpate the dorsal laryngeal area for evidence of laryngeal luscle atrophy Endoscopy at rest - evaluate for asymmetry and asynchrony Listen to respiratory sounds during fast exercise Exercising endoscopy
37
Recurrent laryngeal neuropathy (RLN) - grading
1= normal to 4 = total hemiparesis. Grades 1+2 unlikely to be associated with collapse during exercise, Grade 3 = equivocal, Grade 4-> always collapse + require tx. Grades 1+ 2 = v. unlikely to be clinically signficiant Grade 3 (3 subgrades : 3.1, 3.2, 3.3) = equivocal □ May be normal or abnormal during exercise □ Exercising endoscopy recommended Grade 4 = will definitely be clinically significant
38
Recurrent laryngeal neuropathy (RLN) - treatment
No treatment necessary if horse is not performing athletically Mild cases/non-performance horses -> ventriculectomy ("Hobday's operation"), or ventriculocordectomy (remove laryngeal ventricle and the vocal cord). Severe cases -> left sided laryngoplasty surgery AKA ‘tie-back’ = 2 x permanent sutures placed to mimic action of atrophied CAD muscle -> permanent abduction of left arytenoid.
39
Bilateral laryngeal paralysis
Uncommon Causes: hepatic encephalopathy, organophosphate or lead poisoning, after general anaesthesia, laryngeal dysplasia. Can cause life threatening airway obstruction therefore temporary tracheostomy should be performed and the underlying cause treated if possible. If severe may need emergency tracheotomy
40
Arytenoid chondritis
uncommon in UK, common in USA Racing on dirt tracks (c.f. grass) predisposes.
41
Arytenoid chondritis - clinical signs
abnormal respiratory noise (at rest if severe), coughing during eating
42
Arytenoid chondritis - diagnosis
Endoscopically: swollen, uneven contour, reddened arytenoid cartilages unilaterally or bilaterally, +/- mucosal ulceration, granulomas and draining sinus tracts and reduced motility. N.B. left sided chondritis can resemble RLN due to laryngeal asymmetry present. Additional Dx – ultrasound larynx and see thickened arytenoid body.
43
Arytenoid chondritis - treatment
medical if mild (long term abios, NSAIDs +/- throat sprays) or partial arytenoidectomy (surgery via laryngotomy) Resection of most of the arytenoid cartilage About 75% return to racing
44
Arytenoid chondritis - prognosis
Poor prognosis if bilateral
45
Arytenoid chondritis - major complication
Aspiration of food
46
Medial deviation of the ary-epiglottic folds
Common Actually the most prevalent abnormality seen on exercising endoscopy, very often in conjunction with other disorders e.g. DDSP, RLN etc. Cause of abnormal noise in racehorses
47
Medial deviation of the ary-epiglottic folds - clinical signs
Medial ‘bowing’ of the mucosal ary-epiglottic folds during inspiration results in high pitched inspiratory whistle (DDx vocal fold collapse in a mild RLN case). If severe can cause respiratory obstruction.
48
Medial deviation of the ary-epiglottic folds - diagnosis
Exercising endoscopy required to diagnose
49
Medial deviation of the ary-epiglottic folds - treatment
resection of ary-epiglottic folds. Transendoscopic laser treatment (sedation) Open surgery under GA (laryngotomy incision)
50
Laryngeal dysplasia (AKA: 4th +6th branchial arch defects)
Rare congenital abnormality -> variable abnormal/missing cricopharyngeus muscle (upper oesophageal sphincter mm), parts of the thyroid and cricoid cartilage unilaterally or bilaterally plus rotation of the larynx to one side.
51
Derivatives of the 4th branchial arch
Thyroid cartilage Cricoid cartilage Cricopharyngeus mm (upper oesophageal sphincter) Crico-thyroideus mm
52
Laryngeal dysplasia (AKA: 4th +6th branchial arch defects) - clinical signs
Onset at any age Most common cause of RIGHT sided laryngeal dysfunction - but can be left or bilateral Severity depends on severity of defects abnormal respiratory noises, performance +/- belching/colic due to aerophagia.
53
Laryngeal dysplasia (AKA: 4th +6th branchial arch defects) - diagnosis
laryngeal palpation -> feel abnormal gap between cricoid and thyroid. Endoscopy at rest -> variable changes present but laryngeal dysplasia is the most common cause of RIGHT sided laryngeal dysfunction. Radiography (unsedated)-> may see air in proximal oesophagus, RDPA visible as fold of soft tissue over dorsal arytenoid cartilages Laryngeal ultrasound gives further weight to diagnosis as abnormalities in cartilage structure seen
54
Laryngeal dysplasia (AKA: 4th +6th branchial arch defects) - treatment
None very effective! Vocal cordectomy if mild ?Tie back affected side ?Arytenoidectomy Tracheotomy tube/tracheostomy Retire to less strenuous work
55
Epiglottic retroversion
At exercise only – causes intermittent inspiratory obstruction Often a strange ‘gulping’ noise Tx = epiglottic ‘tie-down’ surgery
56
Crico-tracheal ligament collapse
Very rare Requires exercising endoscopy

Equine II (28 decks)

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