Overview ↑ O2 demand → ↑ respiratory rate and ↑ tidal volume → ↑ minute ventilation ↑ O2 consumption and ↑ CO2 production Arterial blood no change in PaO2 and PaCO2 ↑ minute ventilation and ↑ efficiency of gas exchange ensure that there is neither a decrease in PaO2 nor an increase in PaCO2 ↓ pH during strenuous exercise secondary to lactic acidosis Venous blood ↑ PvCO2 skeletal muscle adds more CO2 than usual to venous blood no change in PaCO2 sufficient ↑ minute ventilation to remove excess CO2 Pulmonary blood flow ↑ cardiac output → ↑ pulmonary blood flow → ↓ pulmonary resistance pulmonary blood flow becomes more evenly distributed throughout lungs V/Q ratio from lung apex to lung base becomes more uniform ↓ physiologic dead space Oxygen-hemoglobin dissociation curve ↑ tissue PCO2, ↓ tissue pH, and ↑ temperature → shifts to right ↓ hemoglobin affinity for O2 → ↑ O2 unloading in exercising skeletal muscle Chronic changes include ↑ cardiac chamber size and ↑ wall thickness due to hypertrophy ↑ ejection fraction and ↑ cardiac output due to greater efficiency ↑ maximum oxygen consumption (VO2 max) during exertion