Blood flow, Gas transport, and maximal aerobic power Flashcards
Stroke volume
the amount of blood pumped from the right or the left ventricle per beat (ml)
Cardiac output (Q)
the amount of blood pumped from the left r right ventricle of the heart per minute (L/min)
- the right and left ventricles must have the same cardiac output so that blood flow through the pulmonary and systemic circuits is maintained equally
Cardiac output equation
Heart rate (bpm) x stroke volume (ml)
What is the relationship expressed by Fick equation
Since blood transports oxygen, when cardiac output increases with exercise more blood will be transported to working muscles
What is Fick equation
VO2= HR x SV x (a-VO2) diff
VO2
oxygen uptake or utilization by tissues of the body
(a-VO2)
arterial mixed venous oxygen difference
To increase oxygen uptake what must you do?
increase cardiac output or extract more oxygen from arterial blood
Higher maximal stroke volume means
higher maximal cardiac out —> higher maximal oxygen uptake (VO2max)
Cardiac output rises for a given work rate
Therefore the cardiac output required for a given workload is reasonably similar for an untrained and trained athlete
what happens to heart rate when the work rate increase
Heart rate increases linearly with increasing workload till the subject’s maximum heart rate is reached
For any given workload (VO2), what is true about VO2 subjects
- trained subjects have a lower exercise heart rate and higher stroke volume than untrained subjects
Why is the heart rate at a given oxygen uptake higher when the exercise is performed with the arms than the legs?
- smaller muscle mass
- increased intra-thoracic pressure
- less effective muscle pump
- feedback to control center
Stroke volume equation
end-diastolic volume - end systolic volume
Diastole
the resting phase of the cardiac cycle, between heartbeats
- filling up hear
Systole
the contraction phase of the cardiac cycle, when the ventricles pump out their stroke volume
End-diastolic volume (EDV)
the volume of blood in each ventricle at the end of diastole
End-systolic volume (ESV)
the volume of blood that remains in each ventricle after the ventricles finish contracting
Ejection fraction
the percentage of EDV ejected with each contraction
Ejection fraction increases with
exercise
Ejection fraction
EF (%) = SV / EDV
Max heart rate equation
220 - Age (-+ 12bpm)
Stroke volume increases to its highest values during ______________
submaximal exercise (~40% VO2 max)
Mechanism of increase in stroke volume during exercise
- greater systolic emptying = greater ejection fraction
- the heart has functional residual volume, at rest in the upright position, only 50-60% of blood in the ventricle is pumped out during contraction - 50-80ml of blood remains in the ventricle
- during graded exercise, heart rate increases stroke volume by means of a more complete emptying during systole , due to effect of sympathetic hormones
Distribution of blood flow during exercise
- at rest 15-20% of systemic blood flow goes to skeletal muscle
- during maximal exercise, 85% of cardiac output can be diverted to the working skeletal muscle
The increased blood flow to working muscle is caused by:
- increased blood pressure
- dilation of arterioles in working muscle due to relaxation of smooth muscle in the walls of the arterioles
- Constriction of the arterioles in the gut area (liver, stomach, intestines, kidneys) and non-working muscles
Poiseuille’s Law
Resistance to flow = Fluid viscosity x tube length/ radius of tube (power of 4)
VO2 max provides what info
the maximum oxygen uptake provides important information on the capacity of the oxygen transport system
The most important factors that determine VO2 max
- the ability to ventilate the lungs and oxygenate the blood passing through the lungs
- the ability for the heart to pump blood -cardiac output
- The oxygen carrying capacity of the blood
- The ability of working muscle to accept a large blood supply
- The ability of muscle fibers to extract oxygen from the capillary blood and use it to produce energy (oxidative enzyme level)
VO2 max test protocals
- The test protocol should exceed 6 minutes, but be less than 15 minutes
- It should incorporate a warm-up period (first stage of the test)
- The test protocol should be arranged in stages, with each stage progressively increasing intensity until the termination stage is reached
Criteria for reaching VO2 max
- the oxygen consumption ceases to increase linearly with increasing work rate and approaches plateau (last 2 values agreeing within 2ml/kg/min)
- Heart rate should be close to age predicted maximum heart rate (220-age)
- blood lactate levels should be 8 millimoles/liter or greater, 3-5 min post exercise
- respiratory exchange ratio greater than 1.15 (VCO2/VO2)
- subject obeservations (did subeject look exhausted?)
Why should athletes be tested in the mode of exercise used in their sport?
- Higher VO2 max
- local muscle capillarization and aerobic enzyme levels are important determinants of VO2 max
Why is VO2 max higher on a treadmill and by how much?
- 5-7% higher than on a bicycle
- Due to the activation of larger muscle mass on the treadmill
What are the 2 types of ergometers
- Mechanical - monarch ergometer
- Electrically braked bicycle ergometer
- resistance is provided by moving a conductor through a magnetic field
advantages of using bicycle ergometers vs. treadmills to test exercise
- less expensive
- portable -used in field studies
- don’t require electricity
- patient is more stable and body weight is supported (easier to collect physiological data)
- easier to quantify work rate
Disadvantages of bicycle ergometers
- cant obtain as high of a VO2 max as on a treadmill
- Cycling is not a common mode of movement for most. walking is a far more common activity
How much of VO2 max is genetically determined
40-50%
Improvements in aerobic capacity with training normall range between
6 and 20%
At what age does VO2 max reach its peak
between 18 and 25 years of age then declines 1% per year, so by the age of 55 it is on average 25-30% below reported values for a 20-year-old
Reasons for VO2 max difference in sex
- the difference in body composition (males have more muscle and less fat - muscle is metabolically a more active tissue)
- avg male has 10-14% higher hemoglobin concentration
Reasons for VO2 max decline
- decrease in maximum heart rate, stroke volume, and cardiac output
- negative change to oxygen transport systems
- less physically active as aging
Why use a predictive test to predict VO2 max
- less expensive and less specialized equipment required
- test can be submaximal
- some tests can be administered to large groups
- less motivation is required by the subject
Predictions based on heart rate during exercise are based on what assumptions
- linear relationship between heart rate and oxygen uptake (true sometimes, but in heavy work rate VO2 max increases relatively more)
- similar maximum heart rate for all subjects (SD: +-10 beats/min)
- fixed mechanical efficiency is assumed
- Day-to-day variation in heart rate (+-5 beats/min)
Mechanical efficiency on a bike
may vary by 6%
The efficiency of muscular work
percentage of chemical energy converted to mechanical energy with the remainder lost as heat
Computation of mechanical efficiency (%EFF)
Work Performed (kcal) /Energy (kcal)
