The equine athlete + respiratory causes of poor performance

Question 1

What is the primary function of the respiratory system?

Answer 1

• Gas exchange

Question 2

What is secondary functions of the respiratory system?

Answer 2

• humidification, filtering & warming of air
• thermoregulation
• phonation & olfaction
• acid-base regulation
• blood filtering & pulmonary defence mechanisms

Question 3

Where is resistance higher?

Answer 3

• 80-90% of resistance in URT
• Resistance = proportional to radius

Question 4

How does respiratory function increase during exercise?

Answer 4

• Increase ventilation - increase TV, frequency + decreased dead space
• Increase perfusion - Increased CO + decreased transit time
• Increased diffusion - gradient, blood flow
• Increased haemoglobin conc - o2 carrying capacity (splenic reserve)
• Increased diffusion at tissues - oxyhaemoglobin curve shifts to the right

Question 5

What are respiratory causes of poor perfomance?

Answer 5

• Increased pulmonary resistance - URT disorders, resistance, turbulence, small airways (Hypersecretion, blood, inflammation)
• Decreased alveolar / pulmonary compliance - oedema, hypertension, fibrosis. interstitial disease
• Dynamic airway collapse - inflammatory airway disease, tracheal collapse
• Respiratory muscle / chest wall disease
• Decreased cardiac output - decreased lung / tissue perfusion
• Decreased haemoglobin

Question 6

What is the pathogenesis of exercise induces pulmonary haemorrhage?

Answer 6

• Capillary stress failure
• Cardiac output + blood pressure increase dramatically
• Negative pressure increased in dorsal lung during inspiration

= capillary wall rupture + haemorrhage (progressive + irreversible)

Question 7

What are risk factors of EIPH?

Answer 7

– Speed
– Light jockeys
– Previous EIPH
– Number of years in training
– Hard ground/bar shoes
– Cold external temperatures
– Upper airway disorders

Question 8

What is clinical presentation of EIPH?

Answer 8

• Racehorses within 4 hrs of intense exercise
• also seen in barrel races, showjumpers, polo ponies
• bursts of speed +/- breath holding
• Bilateral epistaxis
• Poor performance
• Caudodorsal lungfield

Question 9

How is EIPH diagnosed?

Answer 9

• Clinical exam
• Tracheal endoscopy <2hrs post-race (presence of blood + grading)
• BAL <14days post-race (RBCs, haemosiderophages + low grade inflammation)
  *Imaging (rarely required)

Question 10

How do you score EIPH?

Answer 10

• 0-1 not bad
• 3-4 very bad

Question 11

How do you treat EIPH?

Answer 11

• Rest + supportive care
• Anti-inflammatories?
• If severe = blood transfusion

Question 12

What does EIPH cause?

Answer 12

• Fibrosis

Question 13

How does EIPH cause fibrosis?

Answer 13

• Intrapulmonary blood provokes macrophage influx and activation.
• The influx of inflammatory cells results in reversible disruption of the alveolar septal architecture.
• The chronic macrophage activity coincides with the development of alveolar septal wall thickening and fibrosis.
• Alveolar septal fibrosis is likely to result in permanent alterations to the alveolar blood-air barrier and reduce local pulmonary compliance

Question 14

How is EIPH managed?

Answer 14

• Reduce incidence - Furosemide 4hrs before intense exercise ( not allowed on day of racing in UK)
• Rest after episode
• Adjust training