Updated: 5/1/2020

Response to Exercise

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Questions
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Topic
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

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Questions (3)
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(M1.PL.15.23) A person is exercising strenuously on a treadmill for 1 hour. An arterial blood gas measurement is then taken. Which of the following are the most likely values?

QID: 100826
1

pH 7.38, PaO2 100, PCO2 69 HCO3 42

11%

(9/81)

2

pH 7.36, PaO2 100, PCO2 40, HCO3 23

69%

(56/81)

3

pH 7.32, PaO2 42, PCO2 50, HCO3 27

6%

(5/81)

4

pH 7.56, PaO2 100, PCO2 44, HCO3 38

4%

(3/81)

5

pH 7.57 PaO2 100, PCO2 23, HCO3 21

7%

(6/81)

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Evidence (4)
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