Updated: 5/1/2020

Response to Exercise

Topic

Review Topic

N/A

Questions

100%

Evidence

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

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pH 7.38, PaO2 100, PCO2 69 HCO3 42

10%

(10/100)

pH 7.36, PaO2 100, PCO2 40, HCO3 23

69%

(69/100)

pH 7.32, PaO2 42, PCO2 50, HCO3 27

(7/100)

pH 7.56, PaO2 100, PCO2 44, HCO3 38