12 control of cardiac output Flashcards
What is P in an electrocardiogram?
atrial systole
What is QRS in an electrocardiogram?
spread of electrical impulses through the ventricles through bundle of his –> purkinje fibres –> ventricular systole and atrial diastole
What is T in an electrocardiogram?
ventricular diastole
What is QT in an electrocardiogram?
Time between depolarisation if ventricles and relaxation
What are the factors effecting cardiac output?
- stroke volume
- heart rate
What is cardiac output?
the amount of blood ejected per ventricle per minute
What is stroke volume?
volume of blood ejected per ventricle per minute
CO of an athlete vs. non athlete
rest: A-5.5 NA - 5
after exercise: A-30 NA-20
L/MIN
SV of an athlete vs. non athlete
rest: A-100 NA-65
After exercise: A-165 NA-105
HR of an athlete vs. non athlete
Rest: A-55 NA-75
After exercise: A-180 NA-190
Heart weight of an athlete vs. non athlete
500 vs 300g
What is stroke volume governed by?
-End diastolic volume
-End systolic volume
(mainly diastolic coz what enters the heart must leave the heart)
How is the heart rate slowed down?
The vaygus nerve which acts on the SAN and releases acetylcholine
How is the heart rate increased?
The accelerator nerve which acts on the SAN and releases norepinephrine/noradrenaline
What is a positive chonotropic effect?
Increases the heart rate
Name 4 things that have a positive chonotropic effect on the heart
- norepinephrine
- adrenaline
- glucagon
- thyroid hormones
What part of the brain is responsible for the heart
pons?
where does adrenaline/ noradrenaline come from?
Adrenal gland
sympathetic nerves
kidneys
How do positive chonotopic substances work?
they cause a faster inflow of sodium and calcium ions which causes the threshold to be reached much faster. reduced repolarisation (below the line) so there can be more depolarisation
How does acetylcholine work on the heart?
It causes K to leave the cell faster and so causes slower depolarisation. its all about what happens before threshold potential is reached - after that its all the same
-the membrane becomes more hyper polarised
acts on the muscarininc K channels (more neg)
What is the HR if you cut the vaygus nerve?
110
What happens to HR if you inhibit ACH
it increases from 70 to 110
What is fast heart rate called?
Tachycardia
What is a slow heart rate called?
Bradycardia
Why do some people have a lower heart rate? (e.g. athletes)
Increased vaygal tone –> more ACH acting on SAN
What is the the preload?
The pressure exerted on the ventricles by the filling of blood. can be measured using the EDV. the amount of blood entering the ventricles/atria
How do you work out stroke volume?
EDV-ESV
What is the afterload?
the end load against which the heart contracts to eject blood from the ventricles
What effects the afterload
- preload volume
- aortic pressure (^=^)
- vasoconstriction
What is contractility?
The energy of contraction regulated by SNS and adrenaline
