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 O 2 uptake to a point, then plateaus with increased speed –VO 2 max

VO 2 max 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 ml O 2 /kg/min –Thoroughbreds160 ml O 2 /kg/min –Greyhounds100 ml O 2 /kg/min –Camel 51 ml O 2 /kg/min

VO 2 max can be used as an assessment of fitness (ability for aerobic energy transfer) VO 2 max reached at heart rate of approx. 200 bpm horses have higher VO 2 max 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 O 2 and enhances O 2 diffusion

Carbon Dioxide Transport dissolved CO 2 in plasma –5% carbamino compounds - combined with and amino group –15-20% combined reversibly with H 2 O –60-80% –CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - with excessive exercise (100% VO 2 max), some CO 2 not eliminated; unique to horse

Oxygen Transportation small amount dissolved in blood (< 2%) combined with hemoglobin (98 %) 4 O 2 molecules per hemoglobin (oxyhemoglobin) Hemoglobin –each gram of oxygen-saturated hemoglobin binds 1.34 ml O 2 –15 g Hg = 20.1 ml/100 ml blood –20 g Hg = 26.8 ml/100 ml blood –anemia - decreased hemoglobin - O 2 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 O 2 more readily to muscle higher pH in lung, hemoglobin loads up on O 2 muscle pH decreases with exercise –increases in arterial PCO 2 in blood unloads more O 2 –temperature right shift with increases blood temperature hemoglobin unloads more O 2 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 O 2, CO 2 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 “ O 2 debt ” –deep breaths to 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