*20 Exercise Physiology Flashcards
1
Q
Normal physiologic response to exercise
- Skeletal muscle contraction
- ATP
- If O2 supplies are inadequate,…
A
- 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
Q
Normal physiologic response to exercise
- CO2
- During exercise, muscle cells…
- Exercise-induced lactic acidosis also causes…
- Related equation
A
- 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
Q
The role of the cardiovascular and respiratory systems during exercise
- The cardiovascular system
- The respiratory system
- PCO2 equation
- Lactic acidosis equation
A
- 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
Q
The physiology of exercise:
Incremental cardio-pulmonary exercise test
- Incremental cardio-pulmonary exercise test
- VO2 and VCO2
- CO2 production and O2 consumption
A
- 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
Q
The physiology of exercise:
Incremental cardio-pulmonary exercise test
- Anaerobic threshold
- Minute ventilation
- Initially
- Once anaerobic threshold is reached
- Later
A
- 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
Q
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…
A
- 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
Q
Exercise limitation
- In the presence of disease, exercise capacity can be limited either by…
- Factors that can significantly reduce exercise capacity
A
- 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
- Factors that impair tissue oxygen delivery
8
Q
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…
A
- 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
Q
Exercise limitation
- Cardio-pulmonary exercise tests are interpreted by…
- Abnormal exercise capacity is indicated by…
- If exercise capacity is abnormal, we then determine…
A
- 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
Q
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
A
- 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
Q
Characteristics of an exercise study
- (Predicted) VO2 max
- Normal
- Cardiovascular limitation
- Respiratory limitation
- (Predicted) HR max
- Normal
- Cardiovascular limitation
- Respiratory limitation
A
- (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
Q
Characteristics of an exercise study
- (Predicted) VO2 max
- Normal
- Cardiovascular limitation
- Respiratory limitation
- (Predicted) VE max
- Normal
- Cardiovascular limitation
- Respiratory limitation
A
- (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