Cardiac Physiology Flashcards
What is the end systolic volume (ESV)?
The ESV is the volume of blood in the heart after systole or a contraction - this is also the point where diastole or relaxation of the heart muscle is about to begin.
What is the end diastolic volume (EDV)?
The EDV is the volume of blood in the heart and the end of diastole or the “filling” stage of the cardiac cycle - this is also the point where systole (or contraction) is about to begin.
What is the stroke volume?
Stroke volume is the difference between EDV and ESV
or amount of blood pushed out of the heart per heart beat SV= EDV - ESV
What is the ejection fraction?
Ejection fraction (EF) is the stroke volume divided by the EDV. It is the proportion of blood (when at maximum blood filling) that is ejected into systemic circulation. EF = SV/EDV
What is (under normal circumstances) a normal EF?
55-60% - the heart does not normally eject all of the blood in the heart.
What is cardiac output?
Cardiac output is the volume of blood that the heart is ejecting per unit of time.
CO = HR x SV
What is venous return?
Venous return is the amount of blood returned to the heart via the venous system.
Since the circulatory system is a closed system, which value should the venous return be equal to?
The cardiac output - the amount of blood returned to the heart should be equal to amount of blood leaving the heart.
What is the total peripheral resistance (TPR)?
The total peripheral resistance is the resistance to blood flow from peripheral structures (like the organs and arteries of the body).
Would vasoconstriction lead to an increase or decrease in TPR?
An increase in total peripheral resistance since the diameter has decreased when the vessel is vasoconstriction.
Would vasodilation lead to a decrease or increase in TPR?
A decrease in TPR since the diameter of the vessels has increased.
During exercise the body aims to maximise blood flow to which areas?
The heart and skeletal muscles.
What is the trigger for blood divergence to the heart and skeletal muscle during exercise?
Muscle hypoxia - lack of oxygen to skeletal muscle tissue.
As the muscles are contracted ATP is used - this leads to decreased oxygen which results in localised hypoxia of muscle tissue.
What arm of the autonomic NS mediates the body’s response to exercise?
Sympathetic NS
Name some mediators released into the blood stream causing vasodilatation as a result of exercise.
Adenosine
Lactate
Carbon dioxide
Potassium
A key physiologic response during exercise is vasodilation. TPR is decreased when there is vasodilation - what would be the benefit of decreasing TPR?
Decreased TPR activates the SNS which allows key changes to take place during exercise (e.g. increased HR, contractility).
A drop in TPR (associated with exercise) leads to activation of what?
The SNS
List the SNS changes associated with exercise.
Increased contractility - increases SV
Increased HR - increases CO
Divergence of flow- decreased to GIT and increased flow to skeletal muscle.
During exercise will the systolic blood pressure rise or fall?
The SBP will rise - this is because the cardiac output is increasing (resulting in more blood in the vessels) and more pressure (more work done by the heart).
During exercise does the diastolic blood pressure stay normal, rise or fall
The DBP will usually decrease slightly or stay normal - this is because of a drop in TPR (localised blood vessels near skeletal muscle will vasodiliate (resulting in a fall in resistance from peripheral structures).
Why does the partial pressure increase during exercise?
The partial pressure rises during exercise because there is a widening of the difference between SBP and DBP - recall the equation for PP= SBP - DBP
Fill in the blanks.
During exercise there is a __________ (decrease/increase) in diastole duration leading to ________ (increased/decreased) coronary filling time.
decrease; decrease
During exercise the HR increases so there is less ventricular filling time - this leads to less blood in the coronary arteries.
In order to combat the decrease in diastole during exercise, the coronary arteries must ___________ to ensure adequate perfusion of heart tissue.
vasodilate
During exercise the heart has increased oxygen demand - what will the heart do in order to increase oxygen supply to the myocardium? A) arterial vasodilation B) increase PaO2 C) vasodilation of coronary vessels D) increase haemoglobin
C) vasodilation of coronary vessels
The heart tissue is already at maximum oxygen extracting capacity - vasodilation will increase amount of blood.
Wrong answers -
A - will not affect myocardial blood supply and is a PNS response.
B - the body is not physically able to increase PaO2!
D- the body cannot change haemoglobin content in the blood
Does preload increase or decrease during exercise?
The preload increases
The increase in venous contraction due to sympathetic innervation causes a rise in _______ and _______.
preload and EDV - this also leads to a rise in cardiac output.
Does the ejection fraction increase or decrease during exercise?
The EF increases - due to more vigorous contractions
The end systolic volume decreases during exercise. Why is this?
The contractility of the heart increases during exercise - less blood is left within the left ventricle and being pumped into the systemic circulation.
The EDV only changes minority during exercise. Why is this?
The HR rises during exercise - there is less ventricular filling time and as such less blood is able to be filled when the heart is relaxed.
Using your knowledge of the changes to EDV and ESV during exercise, why does the EF increase.
The ESV decreases and EDV decreases (minorly) so following the EF equation - EF= EDV-ESV/EDV the major decrease in ESV will cause the EF to rise.
What does Lusitropy mean?
Lusitropy describes myocardial relation (it is essentially the opposite of contractility). - how vigorously the walls of the left ventricle come apart during diastole
During exercise lusitropy does what?
It increases - which results in an increase in preload and CO.
Lusitropy is the rate of myocardial relaxation. What is the name of the key regulatory protein during lusitropy?
Phospholamban
Which enzyme does phospholamban inhibit?
SERCA - sarcoplasmic reticulin calcium - ATPase
What is the function of the enzyme SERCA in cardiac myocytes?
SERCA regulates calcium uptake from the cytosol of cardiac myocytes into the sarcoplasmic reticulum.
SERCA is a pump that transports calcium ions from the cytoplasm into the sarcoplasmic reticulum. Its action can be inhibited by phospholamban. How can the inhibitory effects of phospholamban on SERCA be reversed?
Beta adrenergic stimulation will cause phosphorylation of phospholamban - reversing its inhibitory effects on SERCA
What is the effect of SERCA?
SERCA is an ion channel which allows re-uptake of calcium ions into the sarcoplasmic reticulum.
In the heart, this causes a DECREASE in contractility as calcium ions are stored within the SR.
Describe the concept of auto regulation of organs with changing blood pressure.
Autoregulation describes the changes in blood pressure and flow occurring in the body and how organs combat these changes using local metabolites to determine the degree of vasoconstriction.
What local metabolites does the heart use in auto-regulation?
carbon dioxide
adenosine
nitric oxide
What local metabolites does the brain use in auto-regulation?
carbon dioxide
pH of blood
What local metabolites does the kidneys use in auto-regulation?
blood pressure
NaCl (delivered to the macula densa cells)
How do the lungs control blood pressure through the mechanism of vasoconstriction?
Hypoxia is a trigger for the lungs to vasoconstrict.
What local metabolites does skeletal muscle use in auto-regulation?
Lactate
Adenosine
Potassium
