Dynamic respiratory tract Flashcards
How much air does a galloping horse require?
1500 L/min of air
Which are the non-rigid parts of the upper airway?
nostrils, nasopharynx and larynx
active muscular effort is required to resist collapse and maintain an adequate, functional airway.
Regions of the upper airway with the smallest diameter (and so largest resistance to airflow)
Nostrils
Larynx
When during the stride does inspiration occur?
Inspiration occurs at the canter or gallop as the leading leg is lifted off the ground
Very common URT disorders
Recurrent laryngeal neuropathy,
soft palate disorders,
medial deviation of the ary-epiglottic folds,
vocal fold collapse,
false nostril flutter (high blowing)
Fairly frequent URT disorders
Epiglottic entrapment,
arytenoid chondritis,
laryngeal dysplasia,
nasopharyngeal collapse.
Rare URT disorders
Epiglottic retroflexion,
sub-epiglottic cysts,
epiglottitis,
tracheal collapse,
bilateral laryngeal paralysis,
ventro-medial collapse of the corniculate process of arytenoid,
alar fold collapse (nostrils)
High blowing
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
Nasal paralysis
Facial nn VII damage
Alar fold collapse
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.
Nasopharynx anatomy
Muscular tube
○ Connects nasal/oral cavities -> larynx/oesophagus
Horse has intra-narial larynx
Soft palate divides nasopharynx from oropharynx
Soft palate anatomy
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
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability.
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).
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- incidence
Thought to be most common dynamic respiratory disorder (up to 20% prevalence).
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- clinical signs
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
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- Aetiology
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
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- diagnosis
history of gurgling noise + poor performance, but this method -> 35% misdiagnosis rate
Only way to definitively dx = exercising endoscopy.
Intermittent dorsal displacement of the soft palate (DDSP) and palatal instability- treatment
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!
Permanent DDSP
Rare
Apparent at rest
Nasopharyngeal collapse - incidence
Uncommon
Nasopharyngeal collapse - aetiology
often unknown - thought to be related to neuromuscular dysfunction of the nasopharynx.
Nasopharyngeal collapse - clinical signs
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
