Cardiac anatomy regulation of Q, exercise triggers and cardiac response to exercise Flashcards
what is stroke volume?
Preload - afterload
What is Q?
Cardiac output
What is preload?
the amount of blood in the ventricles before contraction (EDV)
what is afterload?
the amount of blood left in the ventricles after contraction (ESV)
what is the ejection fraction?
of the initial starting volume how much was ejected?
What is the equation for EF?
EF = SV/EDV
what is the equation for Q?
Q = HR X SV
approximately what is the ejection fraction at rest?
70%
what is the shortening fraction?
How much does the chamber reduce in size whilst it contracts
Approximately what is the shortening fraction at rest?
35%
How does preload affect cardiac output?
How well does the chamber fill prior to the hear beating?
How big is the chamber?
venous return - we want optimal venous return
How does afterload affect cardiac output?
How strong are the contractions?
How much resistance was there? A lot of resistance, more will remain in the heart
What factor is force directly related to regarding the hearts contractions?
Muscle cross-sectional area (more muscle, stronger contraction)
What system is adrenaline released from?
Sympathetic
What actions does the autonomic nervous system carry out and give examples?
Subconscious actions in the body e.g. breathing, digestion
What actions does the parasympathetic nervous system bring about?
Rest and digest
What system is your heart a part of?
Autonomic system
what does the parasympathetic nervous system do to heart rate?
Decrease it
The PNS is wired from the CNS to where?(3)
SA node
AV node
atrial muscle
What does the sympathetic nervous system do to heart rate?
increase HR
The SNS is wired from the CNS to where?(3)
SA node
AV node
ventricular muscle
Roughly what is a normal heart rate?
~72/min
What is a limiting factor of how much the ventricles can fill?
Pericardium
What did Stray-gundersen, Circ Res, 1986 find when they studied the hearts of dogs?
pericardectomy in dogs allowed a greater SV and Q and peak VO2
what is the frank-starling principle?
increase stretching of myocardial walls will increase strength of contraction
what type of muscle does cardiac muscle have similar length-tension properties to?
skeletal muscle
what is the cardiac muscle length-tension relationship?
increasing ventricular volume stretches the ventricular muscle towards optimum length. if we over stretch the muscle then the contractile strength starts to break away
how does the heart muscle avoid getting to a point where contraction forces decrease
it becomes stiffer
what is the typical blood volume of adults?
5L
what can reduce blood volume in adults
haemorrhage
dehydration
where is blood flow always maintained?
the brain
how much blood resides in the veins at rest
two thirds
How does the body cope with insufficient blood for maximal exercise?
Blood is shunted away from non-working and towards working muscles to support and sustain that exercise
What causes resistance vessels (arterioles) smooth muscle to relax
vasodilators
Give me examples of some vasodilators
Increase nitric oxide Increase bradykinin Increase prostaglandins Increase K+ Increase Co2 Increase lactate Local decrease in PO2
How does an increase in nitric oxide work as a vasodilator?
as we increase the blood flow through the system that will stretch the endothelium and that will stimulate the endothelium to produce nitric oxide which will further allow the vasodilation
how do vasoconstrictors work?
Increase SNS activity release NE (norepinephrine) has an effect on a small amount of vasodilation (against what we are trying to achieve here).
NE acts on alpha-receptors in smooth muscle to cause constriction
What effects are greater? Vasodilation or vasoconstriction?
vasodilation
How much blood resides in the venous system at rest?
70%
How do we increase venous return?
increase SNS activity
constriction of venous smooth muscle
venoconstriction
How much % of blood shunting occurs through venoconstriction?
20%
why do we promote blood flow back to the central circulation?
stop blood pooling
what is the most important way the blood comes back
muscular pump
how do we enhance various return and why ?
moving - veins embedded within the muscle get squeezed and result in the blood being pushed
what happens in the heart after stole has occurred?
the recoil creates a low pressure environment in the ventricles actively sucking blood towards it to promote the filling
Why does the heart twist when it beats?
action facilitates the wringing out of the blood
How does breating out help push blood back towards the heart?
out increase in thoracic pressure then squeeze the vena cava and helps push blood back towards the heart
How does breating in help suck blood back towards the heart?
♣ the pressure drops there is a low pressure in the thorax facilitate blood being sucked up back towards the heart
what effects how much blood is left in the heart at the end of contraction?
volume of blood in atrial circulation
pressure in aorta at onset at onset of ejection
compliance of aorta
size of pulmonary/aorta lumen
inertial component of the ejecting blood column
systemic vascular resistance
where does the pressure have to be lower in order to allow the blood to squirt into the valves?
ventricle
what are the effects on an increased afterload?
increase preload
Stroke volume will be reduced in the acute phase
Reduced velocity of contraction and ejection in acute phase
Marked increase in myocardial O2 consumption
what are mechanoreceptors?
movement changes
what are metaboreceptors?
metabolic changes
what are baroreceptors?
pressure changes
what triggers the CV response? (3)
mechanoreceptors, metaboreceptors, baroreceptors
what are metaboreceptors sensitive to?
Increase lactate
Increase phosphate
Increase prostaglandins
Decrease pH
where are baroreceptors located?
in walls of the carotid sinus and aortic arch are baroreceptors
where are chemoreceptors located?
in the walls of carotid sinus and aortic arch
what do chemoreceptors sense?
high levels of CO2 in the blood
What is the bainbridge reflex?
Increased cardiac filling elicits tachycardia
Increase right atrium filling from increase venous return, Stretch receptors in the right atria and vena cava stretched, Increased firing rate to brain, Brain increases SNS tone, Increase HR and SV
