Evaluation of the Equine Upper Respiratory Tract Flashcards
What is the speed of horses like? What is required to reach this?
1200 lb horse can run ~55 mph (440 yards in 21 s)
efficient gas exchange
Equine upper respiratory tract:
What is labeled in this endoscopic view of the larynx?
What is the normal resting an exercising respiration rates of horses?
RESTING = 8-20 bpm
- tidal volume = 5 L
- total lung capacity = 40 L
- minute ventilation = 40-100 L
EXERCISING = 80-100 bpm
- minute ventilation = ~1500 L
How do horses breathe?
obligate nasal breather that exhales as forehand contacts the ground
What limits horses’ exercise capacity?
URT resistance to airflow (highest at the nares!)
What is the mechanics of airway flow like with inhalation and exhalation? What commonly increases pressure disparity?
INHALATION = negative pressure collapses URT and pushes air into lungs
EXHALATION = positive pressure dilates URT
What is airway resistance primarily determined by?
airway diameter —> cutting the radius in half increases resistance by a factor of 16
R = (8ul)/r^4
What are the 4 major areas of resistance in the upper airway?
- external nares
- nasal mucosa
- pharynx - soft palate, pharyngeal walls
- larynx - epiglottis, arytenoids
Lower airway resistance:
Airway resistance, upper vs. lower:
What is the major contributor to airway stabilization? How does it maintain stability?
muscle tone
- nervous innervation of cranial nerves
- autonomic effects of adrenaline constricting blood vessels during exercise
(enlarges the lumen!)
Flexing the neck and airway resistance:
constricts larynx
What is the normal inspiration to expiration ratio in horses?
1:1
What muscle of the larynx should be palpated on URT evaluation?
cricoarytenoid dorsalis muscle
What are some ancillary diagnostic aids for the URT?
- endoscopy - at rest, dynamic
- radiographs
- CT, MRI
- ultrasound
- blood work
- lower respiratory tract work up
What is used for URT endoscopy? How is it performed?
1 m, 1-cm flexible endoscope
advanced through the ventral meatus (Y-shaped)
What landmark is used for the pharynx?
dorsal pharyngeal recess
Guttural pouch, endoscopic anatomy:
Larynx, endoscopic anatomy:
What is the preferred way to perform an URT endoscopy at rest? What is it used to diagnose?
no sedation —> drugs can alter arytenoid function (scope trachea and GP, too!)
static lesions
What is the purpose of nasal occlusion during URT endoscopy?
creates negative pharyngeal pressure similar to exercise, which can help visualize arytenoid abduction
(abduction better correlated to swallowing)
What is treadmill-dependent dynamic endoscopy preferred for? What are some concerns?
diagnosing dynamic conditions - DDSP occurs during fatigue, so horse needs to exercise for extended periods
- high intensity (220 bpm)
- safety
- doesn’t perfectly mimic real life
What is considered the best method for performing dynamic endoscopy? How does it compare to the treadmill?
portable endoscope (brings scope to horse)
- more difficult to get to max intensity for racehorses
- mimics real life
- able to review in slow motion (120 breaths/min!)
