Equine athlete respiratory system (Yr 4)

Question 1

what is VO2 max?

Answer 1

maximal aerobic metabolic rate and hence the optimum rate at which the heart, lungs, and muscles can effectively use oxygen during exercise
(relates to endurance performance)

Question 2

what are the secondary functions of the respiratory system?

Answer 2

humidification, filtering, warming air
thermoregulation
phonation/olefaction
acid-base regulation
pulmonary defence mechanism

Question 3

what are some anatomical dead spaces within the respiratory system?

Answer 3

anywhere gas exchange isn’t occurring…
trachea, bronchioles, unventilated alveoli

Question 4

how is gas transported in the blood?

Answer 4

oxygen is partially dissolved but mostly bound to haemoglobin

Question 5

what are the three causes of increased oxygen dissociation into tissues?

Answer 5

increase temperature
decreased pH
increased carbon dioxide

Question 6

what factors decreased pulmonary gas exchange?

Answer 6

increased pulmonary resistance
decreased alveolar/pulmonary compliance
dynamic airway collapse
respiratory muscle/chest wall disease
decreased cardiac output (lung/tissue perfusion)
decreased haemoglobin

Question 7

what does EIPH stand for?

Answer 7

exercise induced pulmonary haemorrhage

Question 8

what is EIPH?

Answer 8

blood present in airways after exercise based on post-exercise endoscopy

Question 9

how does EIPH appear on post-mortem?

Answer 9

caudodorsal areas of blue discolouration of lungs due to the accumulation of haemosiderin (iron pigment) within damaged areas of the lung

Question 10

how can EIPH be diagnosed?

Answer 10

no consistent signs (except epistaxis)
endoscopy post-exercise or BAL looking for haemosiderophages

Question 11

what are the grades of EIPH diagnosed from endoscopy?

Answer 11

1 - flecks of blood or short single stream extending less than a quarter of tracheal length
2 - continuous stream of blood extending at least one half of the trachea
3 - multiple streams covering more than a third of the tracheal surface
4 - abundant/pooling blood

Question 12

why does EIPH occur?

Answer 12

extremely high pulmonary blood pressure
high inspiratory pressures
inflammation
locomotory shockwaves (stomach hitting diaphragm)

Question 13

what causes the prevalence of EIPH to increase in the racing population?

Answer 13

increases with age

Question 14

does EIPH affect performance?

Answer 14

grade 1 and 2 don’t affect normal performance
grade 2 and 3 are associated with poor performance

Question 15

why should horses be rested after EIPH?

Answer 15

blood causes inflammation in the airways

Question 16

why does EIPH cause airway inflammation?

Answer 16

blood is removed an initial neutrophilic inflammation which then triggers a marked macrophage activation for phagocytosis
this leads to some fibrosis within the alveolar walls

Question 17

how may EIPH influence performance?

Answer 17

more severe grades will promote more severe inflammation leading to chronic thickening and fibrosis of the alveolar walls and hence less efficient gas exchange

Question 18

is there any treatment available for EIPH?

Answer 18

no (only furosemide has been shown to improve this as it is a diuretic so reduces circulating pressures)

Question 19

why is the use of furosemide banned in racing?

Answer 19

it is a diuretic so enhances drug excretion