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Flashcards in *20 Exercise Physiology Deck (12)
1

Normal physiologic response to exercise

  • Skeletal muscle contraction 
  • ATP 
  • If O2 supplies are inadequate,...

  • Skeletal muscle contraction
    • Uses up large amounts of ATP, which must be replaced if exercise is to continue
  • ATP
    • Generated primarily through the oxidation of glucose (glycolysis), which is normally followed by the reactions of the citric acid or Krebs cycle and then by oxidative phosphorylation
  • If O2 supplies are inadequate,...
    • Glycolysis converts from an aerobic to an anaerobic process
    • This produces two important physiologic effects
      • (1) it markedly reduces ATP synthesis, which ultimately limits exercise
      • (2) anaerobic metabolism produces a metabolic acidosis through the production of lactic acid

2

Normal physiologic response to exercise

  • CO2
  • During exercise, muscle cells...
  • Exercise-induced lactic acidosis also causes...
  • Related equation

  • CO2
    • Generated as a byproduct of the citric acid cycle
  • During exercise, muscle cells...
    • Produce a large quantity of CO2, which diffuses into the tissue capillaries and is transported to the lungs
  • Exercise-induced lactic acidosis also causes...
    • Increased CO2 production through the carbonic acid - bicarbonate buffer system
  • Related equation
    • H2O + CO2(↑) > H2CO3 > H+(↑) + HCO3-

3

The role of the cardiovascular and respiratory systems during exercise

  • The cardiovascular system 
  • The respiratory system
  • PCO2 equation
  • Lactic acidosis equation

  • The cardiovascular system
    • Must supply sufficient O2 to the muscles to maintain adequate ATP production
    • It does this by increasing CO through an increase in both HR and SV
    • O2 delivery is also determined by the hemoglobin concentration and the hemoglobin O2 saturation
  • The respiratory system
    • Must excrete the excess CO2 produced during exercise
  • PCO2 equation
    • PCO2 = k x VCO2 / VE – VD
    • Alveolar ventilation must increase in proportion to CO2 production in order to maintain a normal arterial PCO2
  • Lactic acidosis equation
    • H2O + CO2(↓) > H2CO3 > H+(↓) + HCO3-
    • Ventilation must also increase to compensate for lactic acidosis, if it occurs

4

The physiology of exercise:
Incremental cardio-pulmonary exercise test

  • Incremental cardio-pulmonary exercise test
  • VO2 and VCO2
  • CO2 production and O2 consumption

  • Incremental cardio-pulmonary exercise test
    • A subject exercises on a stationary bike as the resistance to pedaling is progressively increased
    • During exercise, HR, minute ventilation, oxygen consumption (VO2), and CO2 production (VCO2) are continuously measured
  • VO2 and VCO2
    • Initially increase in proportion to the level of exercise
  • CO2 production and O2 consumption
    • Note that the amount of CO2 produced is initially less than the amount of O2 consumed (remember R ≈ 0.8)

5

The physiology of exercise:
Incremental cardio-pulmonary exercise test

  • Anaerobic threshold
  • Minute ventilation
    • Initially
    • Once anaerobic threshold is reached
    • Later

  • Anaerobic threshold
    • At some point during progressive, incremental exercise, CO will reach a maximum level
    • The cardiovascular system will no longer be able to meet the O2 demands of the exercising muscles
    • At the onset of anaerobic metabolism, the rate of CO2 production increases and it will eventually exceed oxygen consumption (i.e. R > 1)
  • Minute ventilation
    • Initially increases in proportion to VO2 and VCO2
    • Once anaerobic threshold is reached, however, minute ventilation increases at the same rate as CO2 production
    • Later, minute ventilation increases out of proportion to CO2 production as the respiratory system compensates for increasing lactic acidosis

6

The physiology of exercise:
Incremental cardio-pulmonary exercise test

  • The onset of anaerobic metabolism (anaerobic threshold) is determined by...
  • In the absence of cardiovascular or pulmonary disease, maximum exercise is determined solely by...
  • Exercise is typically terminated shortly after...
  • In other words, exercise is normally limited by...
  • Exercise is not normally limited by...

  • The onset of anaerobic metabolism (anaerobic threshold) is determined by...
    • Measuring the VO2 at which the rate of rise in CO2 production and minute ventilation increases
  • In the absence of cardiovascular or pulmonary disease, maximum exercise is determined solely by...
    • The amount of oxygen that can be delivered to the skeletal muscles
  • Exercise is typically terminated shortly after...
    • The onset of anaerobic metabolism
  • In other words, exercise is normally limited by...
    • The cardiovascular system
  • Exercise is not normally limited by...
    • Minute ventilation, which can be increased far above that required during maximal exertion

7

Exercise limitation

  • In the presence of disease, exercise capacity can be limited either by...
  • Factors that can significantly reduce exercise capacity

  • In the presence of disease, exercise capacity can be limited either by...
    • The inability of the cardiovascular system to deliver sufficient oxygen
    • The inability of the respiratory system to excrete the increased CO2 load
  • Factors that can significantly reduce exercise capacity
    • Factors that impair tissue oxygen delivery
      • Primarily low cardiac output
      • Also anemia and hemoglobin desaturation)
    • Factors that impair alveolar ventilation (e.g.)
      • Abnormal respiratory mechanics
      • Increased dead space
      • Rspiratory muscle weakness

8

Exercise limitation

  • In clinical medicine, incremental cardio-pulmonary exercise tests are used to determine...
  • Equations that factor in age, sex, and height are used to predict...
  • Prior to exercise, the maximum voluntary ventilation (MVV) is measured by...

  • In clinical medicine, incremental cardio-pulmonary exercise tests are used to determine...
    • The cause of a patient’s reduced exercise capacity
  • Equations that factor in age, sex, and height are used to predict...
    • Normal maximum O2 consumption, which reflects exercise capacity
    • Normal maximum HR, which reflects cardiovascular function
  • Prior to exercise, the maximum voluntary ventilation (MVV) is measured by...
    • Having the patient breathe in and out as quickly and forcefully as possible for 12 seconds
    • The measured exhaled volume is then multiplied by 5 to predict the maximum minute ventilation that the patient is capable of achieving

9

Exercise limitation

  • Cardio-pulmonary exercise tests are interpreted by...
  • Abnormal exercise capacity is indicated by...
  • If exercise capacity is abnormal, we then determine...

  • Cardio-pulmonary exercise tests are interpreted by...
    • First comparing the actual with the predicted VO2 at peak exercise
  • Abnormal exercise capacity is indicated by...
    • A maximum oxygen consumption that is less than 90% of the predicted value
  • If exercise capacity is abnormal, we then determine...
    • Whether exercise is limited by the cardiovascular or the respiratory system

10

Exercise limitation

  • Patients with a cardiovascular limitation to exercise
    • Minute ventilation
    • Heart rate
    • Anaerobic threshold
  • Patients with a respiratory limitation to exercise
    • Minute ventilation
    • Heart rate
    • Anaerobic threshold

  • Patients with a cardiovascular limitation to exercise
    • Have a maximum minute ventilation that is far below their MVV
    • Have a peak heart rate that exceeds 90% of their predicted value
    • Reach anaerobic threshold early during exercise since tissue oxygen delivery is impaired
  • Patients with a respiratory limitation to exercise
    • Quickly reach their maximum attainable minute ventilation, which will be very close to or even greater than their calculated MVV
    • Since exercise is terminated early, they will not reach their predicted maximum heart rate and often don’t reach anaerobic threshold

11

Characteristics of an exercise study

  • (Predicted) VO2 max
    • Normal
    • Cardiovascular limitation
    • Respiratory limitation
  • (Predicted) HR max
    • Normal
    • Cardiovascular limitation
    • Respiratory limitation

  • (Predicted) VO2 max
    • Normal > 0.9
    • Cardiovascular limitation < 0.9
    • Respiratory limitation < 0.9
  • (Predicted) HR max
    • Normal > 0.9
    • Cardiovascular limitation > 0.9
    • Respiratory limitation < 0.9

12

Characteristics of an exercise study

  • (Predicted) VO2 max
    • Normal
    • Cardiovascular limitation
    • Respiratory limitation
  • (Predicted) VE max
    • Normal
    • Cardiovascular limitation
    • Respiratory limitation

  • (Predicted) VO2 max
    • Normal > 0.4
    • Cardiovascular limitation < 0.4
    • Respiratory limitation > 0.4 (if reached)
  • (Predicted) VE max
    • Normal < 0.7
    • Cardiovascular limitation < 0.7
    • Respiratory limitation > 0.7

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