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The cardiovascular system during exercise college
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Exercise physiology college
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The cardiovascular system during exerciseblock 2.3
The sinus node of the heart determines the HR. The stroke volume is determined by the contractile
force and the arterial pressure (afterload the lower, the higher the stroke volume).
Venous return: the heart can only pump out what it gets in. It stretches the right atrium sinus node
is stimulated HR increases.
Venous blood that stretches the ventricles Frank Starling mechanism: myosin actin act better
contractile force increases.
intrinsic regulation.
Extrinsic regulation: para/ortho sympathic activation:
- Beta adrenergic stimulation and plasma adrenaline increase of sinus node rate, and increase of
contractile force.
- Down side: alpha adrenergic stimulation increases the arterial pressure increase of afterload.
Heart rate is higher when you are standing, stroke volume is higher when yore lying (because of the
increased venous return).
The cardiac ouput increases when you go exercising because of:
- mainly increase of HR.
- Also because of increase stroke volume: but smaller.
Your heart rate is already increased before the race, because of anticipation: stress factors.
Age decreases the maximal heart rate. There is a rule: the maximum heart rate is 220 – age. Its an
approximation, not exactly true, but there is a decrease of heart rate. You have to take this in mind
when someone is doing a maximal bicycle test for example: when we are having a HR of 160 we can
go further, but a person of 50-60 year cant.
The maximal oxygen yptake also decreases with age, but not as much as the HR, because the stroke
volume isn’t decreasing that much.
Factors mediating venous return
The pressure in the venous system is low: no pressure driving the blood to the heart.
- Muscle contraction. Large and smaller veins in the muscles. The larger veins have valves one
directional blood flow. The muscle contraction squeezes blood and lymphe out of the muscle towards
the heart.
- Alpha-adrenergic constriction in veins, and this mobilizes about 10% of blood. About 70% of the
blood volume is distributed in the veins: alpha adrenergic constriction was bad for the arteries, but
good for the veins.
- Lymphatic system:being squeezed by muscle contraction.
- Ventilation: inspiration causes a negative pressure , deeper ventilation: suction pressure sucks the
blood out of your abdomen towards your heart.
PV – loop: starts at point B. Heart is filled passively. Ventricles start to contract, Eject the blood, than
again relaxation. The area under the loop is the work done by the ventricle: the stroke volume.
During exercise the loop becomes bigger:
- Blood pressure is higher.
- Stroke volume is higher.
, The steepness of the line shows an increase of the contractile force of the ventricle that’s the
effect of adrenaline.
Also the filling of the heart is larger: some exercise the filling is bigger. In that case the loop will also
be bigger on the right side.
Sympathatic stimulation is important.
- Para sympathic part: n. vagus to the heart. This starts at the brain stem and goes to the sinal node.
- Sympathetic part: exit from the thoracic levels. These give adrenaline.
Dwarslesie at a high level: vagal nerve still intact, but sympathetic stimulation is disturbed; heart rate
and contractility can not increase as much.
Proces of the contraction of the heart on cellular level
Action potential arrives. Calcium channel opens: enters the cell. This triggers calcium to come out of
the sarcoplasmic reticulum. This goes to the myofibrils and causes the contraction. If you want to
relax: get away all the calcium. In the sarcoplasmic reticulum, there are ATP pumps, that pump in de
Ca back in the Ca stores.Besides calcium is being pomped out via the ca na pomp, caused by the Na K
pomp.
Adrenaline increases the contractility of the cell: The beta receptor stimulation are releasing cAMP
leads to phosphorylation of:
- calcium channels
- troponin.
- SR-Ca2+-ATPase
- Na-K-ATPase
adrenergic stimulation causes proceses by phosphorylation. Leads to more calcium that is coming
faster ,so contraction is coming faster. Also the removal is going faster: peaks are quicker and higher,
and the contractility can increase.
The lines are showing the venous return: the cardiac output increases when there is more
sympathetic stimulation.
Watching soccer:
- HR is 180
- Venous return is less: no muscle contraction.
CO is only about 10, instead of 25. Difference is the venous return which is very important!
Beta blockers lower heart rate. It blocks the increase in heart rate with the duration of exercise.
Normally: stroke volume decreases with increased duration of the exercise: but with beta blockade,
the stroke volume doesn’t decrease that much.
Although there is no sympathic stimulation because of the blockade: you can still exercise! Even with
beta blockers you can still exercise reasonably well.
You block your sympathetic stimulation, but you increase the filling: CO remains on the same level.
Distribution of CO in rest and exercise
CO in rest = 5L/min. CO in exercise = 25 L/min, The most important organ during exercise is the
muscle: 70-85% goes to the muscle. 4-5% goes to the heart muscle. The skin needs more blood
during exercise, dependent on the temperature: 5-20%. The other organs get much less blood. It is
important that you are able to regulate this.
You are able to regulate this by: metabolic (auto) regulation and sympathetic constriction.
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