Gas Exchange

• air > alveoli > blood > hemoglobin in RBC > 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

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

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 > increased RBC > increased hemoglobin > increased affinity of O2 and enhances O2 diffusion

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

Oxygen Transportation

• small amount dissolved in blood (< 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

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

Locomotor-Respiratory Coupling

• effect of natural anatomical driving forces

• walk - no effect

• trot and pace

– ratio 1:, 1:3 or 2:3

• canter and gallop

– 1:1

– compression of chest from driving force of weight on front limbs

– pressure of diaphragm• visceral piston (30% of BW)

– change in axis of body

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

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