Gas Exchange

1
Gas Exchange

• air gt alveoli gt blood gt hemoglobin in RBC gt
  muscle tissue
• normal conditions - oxidative metabolism supplies
  body, matches rate of need
• increased exercise shows linear increase in O2
  uptake to a point, then plateaus with increased
  speed
• VO2max

2
VO2max

• maximal amount of oxygen used by the athlete
  during maximal exercise to exhaustion
• determined by increasing workload or speed of
  treadmill in a stepwise manner
• Humans 69-85 ml O2/kg/min
• Thoroughbreds 160 ml O2/kg/min
• Greyhounds 100 ml O2/kg/min
• Camel 51 ml O2/kg/min

3
VO2 max

• can be used as an assessment of fitness (ability
  for aerobic energy transfer)
• VO2 max reached at heart rate of approx. 200 bpm
• horses have higher VO2max per kg BW
• increased heart size
• increased hemoglobin concentration
• increased peripheral capillary bed
• large skeletal muscle mass has higher density of
  mitochondria (aerobic metabolism)
• spleen gt increased RBC gt increased hemoglobin gt
  increased affinity of O2 and enhances O2
  diffusion

4
Carbon Dioxide Transport

• dissolved CO2 in plasma
• 5
• carbamino compounds - combined with and amino
  group
• 15-20
• combined reversibly with H2O
• 60-80
• CO2 H2O ? H2CO3 ? H HCO3-
• with excessive exercise (100 VO2 max), some CO2
  not eliminated unique to horse

5
Oxygen Transportation

• small amount dissolved in blood (lt 2)
• combined with hemoglobin (98 )
• 4 O2 molecules per hemoglobin (oxyhemoglobin)
• Hemoglobin
• each gram of oxygen-saturated hemoglobin binds
  1.34 ml O2
• 15 g Hg 20.1 ml/100 ml blood
• 20 g Hg 26.8 ml/100 ml blood
• anemia - decreased hemoglobin - O2 content
  decreased
• oxygen dissociation curve

6
Hemoglobin Dissociation Curve

• Bohr effect (triggered by H in blood)
• right shift of curve due to decreased pH of blood
  (acidic)
• hemoglobin unloads O2 more readily to muscle
• higher pH in lung, hemoglobin loads up on O2
• muscle pH decreases with exercise
• increases in arterial PCO2 in blood unloads more
  O2
• temperature
• right shift with increases blood temperature
• hemoglobin unloads more O2 in heated active
  muscle
• not much effect at low intensity work level

7
Locomotor-Respiratory Coupling

• effect of natural anatomical driving forces
• walk - no effect
• trot and pace
• ratio 1, 13 or 23
• canter and gallop
• 11
• compression of chest from driving force of weight
  on front limbs
• pressure of diaphragm
• visceral piston (30 of BW)
• change in axis of body

8
Response to Exercise

• respiration rate and tidal volume increase to
  bodies need
• regulated by chemoreceptors in response to O2,
  CO2 and pH of arteries
• locomotion mechanics override chemoreceptors at
  canter and gallop

9
Recovery Following Exercise

• affected by work intensity, fitness and climate
• rapid decrease in rate, repay O2 debt
• deep breaths to 60-100 bpm
• re-synthesis of phosphocreatine in exercised
  muscle
• catabolism and anabolism of blood lactate
• restore hormonal reserves
• lower body temperature
• regulated by airway and skin temperature
• analysis - rate depth, HR, rectal temperature,
  and physical state