Lecture 10 - Blood Flow, Gas Transport and Maximal Aerobic Power

Question 1

Define: stroke volume

- state the equation

Answer 1

• the amount of blood pumped by either the left or right ventricle per beat
• end diastolic volume - end systolic volume

Question 2

Define: cardiac output

- state the equation

Answer 2

• the amount of blood pumped by either the left or right ventricle of the heart per minute
  Equation: cardiac output = heart rate (bpm) x stroke volume (mL)

Question 3

The left and right ventricles have the same cardiac output. Why is that?

Answer 3

so that blood flow through the pulmonary and systemic circuits is maintained equally

Question 4

State the ficks equation and what it explains

Answer 4

VO2 = HR X SV X (a-vO2) diff

• where VO2= tissue oxygen uptake
• where (a-vo2)diff= arterial mixed venous oxygen difference (the amount of oxygen extracted at tissue capillary beds)
• explains that during exercise, cardiac output increases and more oxygen is transported to the working muscles

Question 5

• concept: how do you increase tissue’s oxygen uptake? (2)

Answer 5

• increase cardiac output

- extract more oxygen from the arterial blood

Question 6

fill in the blank: In general, higher maximal stroke volume means higher ___________, and higher ________

Answer 6

• maximal cardiac output

- maximum oxygen uptake

Question 7

concept: explain the cardiac output, exercise heart rate, and stroke volume differences (if any), between a trained and untrained subject that is given the same workload

Answer 7

• cardiac output: same
• exercise heart rate: trained subjects have a lower HR
• stroke volume: trained subject have a higher SV

Question 8

How does heart rate increase as the workload increases?

Answer 8

• linerally until the maximum heart rate is reached

Question 9

A subject is given 2 exercises but both with the same workload. 1 is done with their arms and 1 with their legs. How does the subject’s heart rate differ in these 2 cases?

Answer 9

• the heart rate is higher when the exercise is performed with the arms

Question 10

How does systole and diastole differ?

Answer 10

• systole: the contraction phase of the cardiac cycle; when the ventricles pump out their stroke volumes
• diastole: the resting phase of the cardiac cycle, between heart beats

Question 11

Explain end-diastolic volume and end-systolic volume

• state the averages of each in an untrained person at rest
• what is ejection fraction?

Answer 11

• End-diastolic volume (EDV): the volume of blood in each ventricle at the end of diastole (120 ml in an untrained person at rest. )
• 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)
• Ejection fraction: the percentage of EDV ejected with each contraction.

Question 12

When is stroke volume at its highest?

At rest, only ____% of blood in the ventricle is pumped out during contraction; How does the body chemically increase stroke volume during exercise?

Answer 12

• 40% of VO2 max (roughly ~110-120 HR)
• remains constant at highest during the progression from moderate to maximal work
• at rest, only 50-60% of blood in the ventricle is pumped out during contraction; sympathetic hormones empty the ventricles more effectively to increase stroke volume;

Question 13

Fill in the blank and answer: at rest ___% of the systemic blood flow goes to the _____. During maximal exercise ___% of the cardiac output can be diverted to the ______. This increase in blood flow to __________ is caused by: (3)

Answer 13

• 15-20%
• skeletal muscles
• 85%
• working skeletal muscles
• working muscles
  1. Increased blood pressure
  2. Dilation of arterioles in working muscles due to relaxation of the smooth muscle in the walls of the arterioles.
  3. Constriction of arterioles in the gut area (liver, intestines, stomach, kidneys) and non- working muscles.

Question 14

Concept: Explain Poiseuille’s Law and give the equation; what does this mean for blood flow?

Answer 14

• explains flow of a liquid in relation to several different factors
• Equation: Resistance to flow = [Fluid viscosity X Tube length]/
  (Radius of tube)^4
• only a small change in blood vessel radius is needed to dramatically alter blood flow

Question 15

What are the 5 main factors that determine a person’s VO2 max

Answer 15

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 (hemoglobin)
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 16

What is VO2 max?

Answer 16

• maximal oxygen uptake;

- maximum rate of oxygen consumption measured during incremental exercise

Question 17

What are some protocols for VO2 max test? (hint: time, first stage, and progression)

Answer 17

• test should exceed 6 min but no longer than 15
• a warm up period should be included (first stage)
• set stages that should progressively increase in intensity

Question 18

What are the 5 main criteria for attaining VO2 max

Answer 18

1. 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 millimoles/liter 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 19

What are 4 factors that impact maximal aerobic power(NOT physiological/related to SV, HR, BP,etc) ?

Answer 19

• mode of exercise
• heredity
• age
• sex

Question 20

Explain how mode of exercise impacts maximal aerobic power; how does max vo2 compare when average subjects test vo2 on a bike vs a treadmill?

Answer 20

• most subjects reach highest VO2max values during uphill treadmill running (5-7% higher than bicycle ergometer due to larger muscle mass on treadmill)
• competitive athletes achieve VO2 max values equal to or greater treadmill scores when doing their own sport

Question 21

Explain the advantages vs disadvantages of using a bicycle ergometer compared to a treadmill

Answer 21

advantages:
1. Less expensive
2. Portable - can be used in field studies
3. Doesn’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
Disadvantages:
1. Can’t obtain as high a VO2max. as on a treadmill
2. Cycling is not a common mode of movement for most individuals.

Question 22

Explain how heredity impacts maximal aerobic power

Answer 22

• VO2 max is 40 - 50% genetically determined. Improvements in aerobic capacity with training normally range between 6 and 20%.

Question 23

On average: men have a maximal aerobic power 20-25% higher than females; why (2)?

Answer 23

• Differences in body composition; men have more muscle and less fat (muscle is metabolically a more active tissue)
• The average male has a 10-14% higher hemoglobin concentration
• note: before puberty there is no significant difference in VO2 max between boys and girls

Question 24

In general: your maximal aerobic power decreases with age; why (2)?

Answer 24

• 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.
• As individuals grow older, they usually become less physically active.

Question 25

Fill in the blank: VO2 max increases with age and peaks between _____ years of age. Then, it declines about ___% per year. By age ____, VO2 max is, on average, _____% below values reported for a 20 year old.

Answer 25

18-25
1%
55
25-30%

Question 26

What are the advantages of using a predictive/indirect test for VO2max (4)?

Answer 26

• less expensive (less specialized equipment required)
• submaximal testing is safer
• can usually be administered to large groups
• less motivation required from subject

Question 27

What are the 4 assumptions you must make when predicting VO2 max using sub maximum heart rate? How close is this predicted max to a person’s actual value?

Answer 27

• There is a linear relationship between heart rate and oxygen uptake (untrue sometimes at heavy WR)
• all subjects of the same age have a similar maximum heart rate
• a fixed mechanical efficiency is assumed when predicting VO2 from work rate (untrue; mech. efficiency can vary)
• heart rate is the same every day (untrue; varies day to day)
• 10-20%

Question 28

How do you estimate a subject’s maximum heart rate?

Answer 28

220-age= max HR

Question 29

How can you calculate efficiency of muscular work? What is the efficiency of large muscle activities (such as: walking, running, cycling)?

Answer 29

Equation:
%eff= [work performed/ energy expended] x100

-20-25%

Question 30

IMPORTANT: Compare the following in trained and untrained individuals

• cardiac output
• exercise heart rate
• stroke volume

Answer 30

• athlete higher (but for a given workload they are similar)
• athletes lower for a given workload (heart can pump blood more efficiently and effectively; more blood pumped per beat)
• athletes higher for a given workload