Cardiovascular Response to Exercise (S1W2) Flashcards
1
Q
Which of these factors are responsive to exercise training?
a. maximum heart rate
b. heart size
c. blood volume
d. haematocirt
A
- heart size
- blood volume
- haematocrit
max heart rate isn’t trainable
haematocrit doesn’t respond that much to training
2
Q
Why does the cardiovascular system adapt to exercise? Acutely
A
- To increase O2 delivery to working muscles by increasing blood flow to the muscles and reducing delivery to low activity tissues
3
Q
Why does the cardiovascular system adapt to exercise? Chronically
A
- To deliver more O2 to active muscle mass: more effective O2 delivery during sub-maximal exercise and increase maximum O2 consumption (VO2 Max)
4
Q
What cardiovascular factors influence oxygen uptake and VO2 max?
A
- Cardiac (heart) structure and function
- Blood (plasma) volume
- Blood flow and distribution
- O2 extraction (arterio-venous difference)
5
Q
What is arterio-venous difference?
A
- The difference in the oxygen content of the blood between the arterial blood and the venous blood
- An indication of how much oxygen is removed from the blood in capillaries as the blood circulates in the body
6
Q
(What factors influence oxygen uptake and VO2 max?) Explain how oxygen extraction is done.
A
- Needle going into an artery - measures the O2 content in the artery (O2 content in blood as it leaves the heart)
- Puncture a vein coming back from the tissue of interest (e.g. leg)
- Any difference between the O2 content tells us how much O2 has been taken up by the muscle
7
Q
Fick equation
A
- VO2 = HR x SV x (a-v)O2 difference
- HR –> heart rate
- SV –> stroke volume
- a-v –> arterio-mixed venous
- Q –> cardiac output (HR x SV)
8
Q
Explain the relevance of stroke volume in the Fick equation
A
- If arterio-mixed venous difference is multiplied by the heart rate and stroke volume, it will tell you how much O2 uptake there is in the whole body
9
Q
How is stroke volume measured?
A
- SV measured with an ultrasound (check dimension of the heart)
10
Q
Adapting to exercise training: How is ventricular mass relevant?
A
- A good indicator of training status
- Untrained = lighter heart
11
Q
Heart structure: key descriptors
A
- Left ventricular mass (muscle bulk of the left ventricle)
- Septum - provides muscle mass
- Left ventricular volume (how much blood fits in the ventricle)
- Left ventricular wall thickness - provides muscle mass
12
Q
True or False? Endurance athletes have larger hearts than controls
A
True
13
Q
True or False? Power athletes have more muscular hearts than endurance athletes
A
True
14
Q
True or False? Endurance athletes have smaller hearts than power athletes
A
False
15
Q
True or False? Endurance athletes have more muscular hearts than controls
A
True but not by much, power athletes vary more from controls in terms of how muscular their hearts are.
16
Q
Explain what preload is
A
- The amount of blood in the ventricle before contraction (end diastolic volume)
- This determines cardiac muscle length before contraction
- The most important determining factor for preload is venous return
17
Q
Preload: aortic and pulmonary valves
A
- Aortic valve goes into periphery and the pulmonary valve goes into the lungs
- If these valves are closed, the heart is being filled (associated with pre-load - how much blood can fit into the heart) (diastole)
18
Q
Preload: mitral and tricuspid valves
A
- If mitral and tricuspid valves are closed, the filling is complete and the aortic and pulmonary valves open, so blood can go into lungs and periphery (systole)
19
Q
Explain what afterload is
A
- The pressure against which the heart must contract (vascular resistance, aortic mean pressure)
- The higher the afterload, the less blood will be ejected per beat
20
Q
What is contractility?
A
- the force that the heart creates
21
Q
Contractility: Explain what the Frank-Starling mechanism is
A
- Based on the length-tension relationship within the ventricle (the greater the stretch, the greater the contraction)
- If ventricular end diastolic volume (preload) is increased, the ventricular fibre length is also increased, resulting in an increased tension of the muscle
- The more full the heart is, the harder it can contract
- The longer the muscle fibre is, the more it can contract
22
Q
What is an athlete’s heart like?
A
- Left ventricular mass is heavier in all athletes
- Left ventricular volume is larger in endurance athletes
- Posterior wall thickness and septal thickness is larger in resistance athletes
23
Q
Endurance athlete’s hearts: why do they have larger stroke volumes?
A
- High preload and eccentric hypertrophy leads to larger stroke volumes (larger chamber) in endurance athletes
- For every heartbeat, the heart muscles are passively extended (eccentric contraction)
- Eccentric hypertrophy leads to larger stroke volumes
24
Q
Resistance/power athletes hearts
A
- Have more muscular walls
- If you contract the muscles, the heart will have to work against higher resistances
- Afterload is high, SV is low, and contractility is high
- The forces come together when the heart constricts
- Concentric hypertrophy and high afterload leads to lower stroke volume because the heart is constricted in resistance/power athletes
25
What 3 factors determine stroke volume?
- preload
- afterload
- contractility
- cardiac output is therefore directly related to venous return and vascular resistance
26
Explaining high blood pressure with smoking
- Explained with afterload - afterload is increased because the vascular system become less compliant, making it tougher to get the blood out into the system
- As a result, contractility has to increase - so blood pressure will be higher (associated with smoking)
27
Endurance training adaptations: stroke volume (SV)
- Best trained = biggest stroke volume
- Larger hearts with training
- Maximum stroke volumes are different
- Preload is higher with endurance training
Stroke volume: Frank Starling
- Large stroke volume = slower heart beat
- Diastolic filling time is longer because the heart is bigger (Frank Starling - the more extended the heart fibres, the higher the contractility - ultimately allows for a higher maximum stroke volume)
28
Endurance training adaptations: heart rate (HR)
- At the same exercise intensity, the person with a high stroke volume will have the lowest heart rate (sub-maximal exercise)
- Maximum heart rate doesn't respond/change with training
29
Endurance training adaptations: cardiac output (Q)
- Similar at the same exercise intensity across all groups
- Closely related to VO2 max (maximum amount of O2 we can utilise during exercise)
- The best trained group have a lower cardiac output at sub-maximum intensity (less blood required - have more efficient muscles that can extract more oxygen)
- Efficiency
○ Training adaptation at sub-maximal exercise
○ Have more efficient muscles - don't need as much blood to reach the muscle to satisfy its requirement
Ability of the muscle to extract O2 is increased so less blood is required
30
Training the heart through increases in blood volume: RBCs and plasma after training
- RBC increases
- Plasma volume increases - increases in plasma proteins, mainly albumin (osmotic effect)
- Ratio of RBC to blood (haematocrit) lowers in better trained people (not a good indicator of training status)
31
Training the heart through increases in blood volume: water and haemoglobin mass after training
- Increase in total body water via alterations in kidney function (results in reduced urine output and increased water retention)
- Increase in haemoglobin mass - increases VO2Max
32
Blood volume changes
- Cross sectional - higher blood volume in trained athletes
- Longitudinal - early changes = plasma volume increases first (in 10 days) then RBCs increase (months) (Haemoglobin concentration and the haematocrit remain more or less the same, but the ABSOLUTE plasma volume and red blood cell number increase)
33
What is blood doping?
- Taking blood, storing it and producing more blood in the body, then re-injecting the old blood so that you have a greater HB mass
- own blood - autologous
- another person's blood - homologous
34
What is EPO?
- erythropoietin
| - induces production of red blood cells
35
Acute blood redistribution
- During rest, the intestines get lots of the cardiac output (~25%), kidneys receive around 20%, as do the muscles
- During heavy exercise, blood is redistributed to where it is required (muscles and skin (cooling))
36
Acute blood redistribution: Regulation via metabolic regulation and temperature
- Muscles detect low pH (during muscle contraction)
- Protons and lactate concentrations increase, O2 concentration decreases, CO2 increases, temperature increases
- Dilates a blood vessel so more blood can arrive at the muscle
37
Acute blood redistribution: Myogenic contraction
- Blood vessel with low pressure opens to allow more blood through it
- Constricts during high pressure to allow blood distribution to other muscles that might not be receiving much
38
Acute blood redistribution: Endothelium
- Innermost wall excretes nitric oxide (vasodilator) - allows us to dilate the blood vessels
- Beetroot juice is high in nitric oxide - can be used to increase endurance capacity
39
Acute blood redistribution: Sympathetic activity
- More stressed = more blood directed to muscles (can run away etc)
- Less blood goes to tissues (fight or flight response)
40
Summary of this lecture
- The concepts of preload and afterload help explain cardiac adaptations to exercise
- "Athlete's heart":
- heavier, with greater capacity to pump blood
- adaptations are sport (exercise) specific. Increases in stroke volume, cardiac output lead to increased VO2 max (also affected by (a-v) O2 difference)
- blood volume: trainable; mainly due to changes in plasma volume
- blood flow: acute and chronic adaptations to exercise
