9. Blood Flow, Gas Transport and Maximal Aerobic Power

Question 1

What is Stroke Volume?

Answer 1

the amount of blood pumped by either the left or right ventricle per beat. (ml)

Question 2

What is Cardiac output (“Q”)?

Answer 2

Cardiac output (“Q”) -
the amount of blood pumped by either the left or right ventricle of the heart per minute. ( L /min)
* Both the left and right ventricles must have the same cardiac output so that blood flow through the pulmonary and systemic circuits is maintained equally.

Question 3

Resting Q vs Maximal Q

Answer 3

Resting Q =
62 bpm X 80 ml = 4960 ml (~ 5L/min)

Maximal Q =
200 bpm X 100ml (sedentary) to 150ml (athlete) = 20 to 30 L /min

Question 4

Fick equation:

Answer 4

Question 5

Relationship between Cardiac Output and Oxygen Uptake?

Answer 5

Therefore, in order to increase oxygen uptake, you must increase cardiac output and/or extract more oxygen from the arterial blood.

• In general, the higher the maximal stroke volume –> higher maximal cardiac output –> higher maximum oxygen uptake (VO2max.)

Question 6

Cardiac Output of Trained vs Untrained Individuals

Answer 6

The cardiac output required for a given workload is similar for trained and untrained subjects as the oxygen cost to do the same amount of work is about the same.

To achieve the cardiac output required for a given workload, trained subjects will have a lower exercise heart rate, as they have a higher stroke volume than untrained subjects.

For any given subject, the heart usually increases linearly with increasing workload until the subject’s maximum heart rate is reached.

The heart rate at a given oxygen uptake (workload) is higher when the exercise is performed with the arms than with the legs.

Question 7

What is Stroke Volume?
in mL

Answer 7

Stroke volume =
end-diastolic volume minus end-systolic volume

Stroke volume = 120ml – 50 ml = 70 ml

Question 8

What is Diastole?

Answer 8

Diastole refers to the phase of the cardiac cycle when the heart’s chambers, particularly the ventricles, relax and fill with blood as they expand, preparing for the next contraction (systole) to pump blood out of the heart.

Question 9

What is Systole?

Answer 9

Systole -
the contraction phase of the cardiac cycle, when the ventricles pump out their stroke volumes.

Question 10

What is End-diastolic volume (EDV)?

Answer 10

End-diastolic volume (EDV) –
the volume of blood in each ventricle at the end of diastole
– 120 ml in an untrained person at rest

Question 11

What is End-systolic Volume (ESV)?

Answer 11

End-systolic volume (ESV) –
the volume of blood that remains in each ventricle after the ventricles have finished contracting
– 50 ml in an untrained person at rest

Question 12

What is Ejection fraction?

Answer 12

the percentage of EDV ejected with each contraction.

EDV = End Diastolic Volume

Question 13

When is Stroke Volume the highest?

Answer 13

Typically, stroke volume is highest during physical activities that require increased oxygen delivery to the body’s tissues, such as during intense exercise or moments of increased demand

Question 14

Mechanism of increase in stroke volume during exercise:

Answer 14

greater systolic emptying =
greater ejection fraction. The heart has a functional residual volume - at rest in the upright position, only 50 - 60% of the blood in the ventricle is pumped out of the ventricle during the contraction - 50 to 80 ml of blood remains in the ventricle.

During graded exercise, the heart progressively increases stroke volume by means of a more complete emptying during systole - due to effect of sympathetic hormones.

Question 15

What is the DISTRIBUTION OF BLOOD FLOW DURING EXERCISE?

Answer 15

At rest 15-20% of the systemic blood flow goes to the skeletal muscles.

During maximal exercise 85% of the cardiac output can be diverted to the working skeletal muscles.

Question 16

How is blood flow increased to the working muscles?

Answer 16

1. Increased blood pressure
2. Dilation of arterioles in working muscles due to relaxation of the smooth muscle in the walls of the arterioles.
   - release of local factors as a result of muscle contraction
3. Constriction of arterioles in the gut area (liver, intestines, stomach, kidneys) and non-working muscles.
   - due to Sympathetic Nervous System stimulation

Question 17

What is Poiseuille’s Law?

Answer 17

• Decreasing tube radius by a factor of 2 will increase resistance to flow by a factor of 16, decreasing flow by a factor of 16.
• A 33 % decrease in the radius of the arterioles will produce a 400 % increase in resistance to flow.
• Thus, a small change in blood vessel radius will dramatically alter blood flow

Question 18

Physiological Determinants of VO2max

Answer 18

The maximum oxygen uptake provides important information on the capacity of the oxygen transport system.

Question 19

The most important factors that determine VO2 max. in a given person are: (5)

Answer 19

1. The ability to ventilate the lungs and oxygenate the blood passing through the lungs
2. The ability of the heart to pump blood - cardiac output
3. The oxygen-carrying capacity of the blood
4. The ability of the working muscles to accept a large blood supply
5. The ability of muscle fibers to extract oxygen from the capillary blood and use it to produce energy - oxidative enzyme levels, etc.

Question 20

Typical Values for VO2max
(ml·kg-1·min-1)

Answer 20

1. Untrained Canadian male (20-29 years)
   - 40-50
2. Untrained Canadian female (20-29 years) - - 30-40
3. World class endurance athlete (M)
   - 80-90
4. World class endurance athlete (F)
   - 65-75
5. Soccer, ice hockey, basketball (M)
   - 54-60
6. Baseball, football, thrower, sprinter
   - 40-50

Question 21

What are VO2 max. Test Protocols
(3)

Answer 21

1. The test protocol should exceed 6 min. but be less than 15 min.
2. Incorporate a warm-up period - the first stage of the test
3. The test protocol should be arranged in stages, with each stage progressively increasing in intensity until the termination criteria is reached.

Question 22

What are the Criteria for Attainment of VO2max? (5)

Answer 22

1. The oxygen consumption ceases to increase linearly with increasing work rate and approaches a plateau, the last two values agreeing within + 2 ml/kg/min.
2. Heart rate should be close to the age-predicted maximum (220 - age). This is test and protocol dependent.
3. Blood lactate levels should be 8 mL/L or greater, 3-5 minutes post-exercise.
4. Respiratory exchange ratio (VCO2 divided by VO2) should be greater than 1.15.
5. Subjective observations - did the subject look exhausted at the end of the test?

Question 23

What Mode of Exercise should be used to test VO2 max?

Answer 23

• In most subjects, the highest VO2 max values can be obtained during uphill treadmill running - 5-7% higher than on a bicycle ergometer, due to activation of a larger muscle mass on the treadmill.
• However, competitive athletes are able to achieve VO2 max values equal to, or higher than, their treadmill scores while doing their own sport.
• Since local muscle capillarization and aerobic enzyme levels are important determinants of VO2 max.,
• Athletes should ideally be tested in the mode of exercise used in their sport,

Question 24

What are the 2 types of Bicycle ergometers?

Answer 24

1. Mechanical - Monarch ergometers in BPK 142 lab
2. Electrically braked bicycle ergometer - resistance is provided by moving a conductor through a magnetic field.

Question 25

What are the Advantages of bicycle ergometers as compared to treadmills for exercise testing? (5)

Answer 25

1. Less expensive
2. Portable - can be used in field studies
3. Don’t require electricity
4. Patient is more stable and body weight is supported - easier to collect physiological data during exercise - heart rate, blood pressure, oxygen uptake, blood samples, etc.
5. Easier to quantify work rate

Question 26

What are the Disadvantages of bicycle ergometers? (2)

Answer 26

1. Can’t obtain as high a VO2max. as on a treadmill
2. Cycling is not a common mode of movement for most individuals. Walking is a far more common activity.

Question 27

What is the effect of Heredity on VO2 max?

Answer 27

• Based on research studies of identical and fraternal twins, current evidence indicates that VO2 max is 40 - 50% genetically determined.
• Improvements in aerobic capacity with training normally range between 6 and 20%.

Question 28

What is the effect of Age and Sex on VO2 max?

Answer 28

• VO2 max.(liters/min) increases with age and reaches it’s peak between 18 and 25 years of age.
  VO2 max. then declines approximately one percent per year so that by age 55 it is on average 25-30% below values reported for a 20-year-old.
• Before puberty, there is no significant difference in VO2 max. between boys and girls.

After puberty, the average male has a VO2 max. (ml·kg-1·min-1) that is 20 - 25% higher than the average female.

Question 29

What are the 2 Reasons for the sex difference when determining VO2 max?

Answer 29

1. Differences in body composition - male has more muscle and less fat - muscle is metabolically a more active tissue
2. Average male has a 10-14% higher hemoglobin concentration

In the normal population, there are many females who have VO2 max. scores higher than less-fit males.

Highest reported values for VO2 max:
Male - 94 ml·kg-1·min-1 - cross-country skier
Female - 77 ml·kg-1·min-1 - cross-country skier

Question 30

What are the 2 Reasons for the age difference when determining VO2 max?

Answer 30

1. Decrease in maximum heart rate, stroke volume and cardiac output in addition to negative changes in other components of the oxygen uptake and transport systems.
2. As individuals grow older, they usually become less physically active.

• Active individuals maintain a higher VO2 max as they age as compared to sedentary individuals. A highly trained 60-year-old can have a higher VO2 max than a sedentary 30- year old.

Question 31

Why Use a Predictive (indirect) Test?
(4)

Answer 31

1. Less expensive and specialized equipment is required.
2. Tests can be submaximal – safer than asking subjects to work maximally
3. Some tests can be administered to large groups
4. Less motivation is required from the subject

Question 32

What assumptions are made when Predictions Based on Heart Rate During Exercise? (4)

Answer 32

1. Linear relation between heart rate and oxygen uptake - true over a wide range of exercise intensities, but in some subjects at heavy work rates VO2 increases more than heart rate.
2. Similar maximum heart rate for all subjects - standard deviation is approximately 10 bpm. about the average maximum heart rate or people of same age group.
   Maximum HR declines with age - must use an age correction factor
   Estimate Maximum Heart Rate with 220 - Age
3. In cases where VO2 is predicted from work rate, a fixed mechanical efficiency is assumed – however, mechanical efficiency may vary by 6% on a bicycle ergometer.
4. Day-to-day variation in heart rate - even under highly standardized conditions (environmental temperature, time of day, diet, drugs, preliminary rest, clothing) the variation in submaximal heart rate is about 5 bpm. with day-to-day testing at the same work rate.

Question 33

How accurate are the Predictions Based on Heart Rate During Exercise?

Answer 33

The VO2 max. predicted from submaximal heart rate is generally within 10 to 20% of the person’s actual value for normal subjects.

The type of subject for whom these tests are poor predictors tends to be in the very low or very high VO2 max categories.

The error in a well-performed direct measurement of VO2 max is ± 4 - 5%

Question 34

What is the Efficiency of Muscular Work?
How is it Measured?

Answer 34

• The efficiency of muscular work is the percentage of chemical energy converted to mechanical energy, with the remainder lost as heat.
• The efficiency of large muscle acVviVes, such as walking, running, and cycling is usually 20% to 25%.