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75 terms

Physiology: Heart as a Pump

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What are the two phases of systole?
- isovolumetric ventricular contraction
- ventricular ejection
isovolumetric ventricular contraction
All valves are closed. Ventricles are contracting on a chamber full of blood, increasing the pressure
When does ventricular ejection begin?
Ventricular ejection starts when the pressure in the ventricles becomes greater than that in the outlet vessels (aorta and pulmonary artery).
What are the two phases of diastole?
- isovolumetric relaxation
- ventricular filling
isovolumetric relaxation
All valves are closed. Muscle relaxes, causing rapid fall of pressure
When does ventricular filling begin?
Ventricular filling starts when pressure in the ventricles becomes lower than in the atria resulting in the opening of the mitral and tricuspid valves
How can you determine resting fiber length?
Using any of EDP, EDV or CVP (central venous pressure). Each of these is proportional to resting fiber length
Atrial kick
The contribution of atrial systole to end-diastolic volume (at the very end of diastasis)
When is atrial systole important?
In the presence of very rapid heart rates that markedly shortens the slow filling phase and may even encroach upon the rapid filling phase, atrial systole may make the difference between an adequate and an insufficient cardiac output. May also be important in mitral stenosis or other diseases where resistance to ventricular filling exists. Atrial fibrillation may be very deadly in these patients because ventricles are not filling
Pulmonary Wedge Pressure
left atrial pressure is usually assumed to be nearly equal to the pulmonary wedge pressure (stop-flow pressure in the last branch of the pulmonary artery completely occluded by a catheter threaded along this artery)
What does ventricular dP/dt estimate?
Myocardial contractility
dP/dt = increase in ventricular pressure/time = rate of ventricular filling
End systolic volume
A significant amount of blood remains in the ventricular chamber at the end of systole. Made of Systolic Reserve Volume and ResiduaI Volume
Residual volume
small amount of blood that remains in the ventricle after maximal ejection (the ventricle never empties completely)
Systolic reserve volume
Mobilized upon demand, e.g. during tachycardia
Stroke volume
volume of blood ejected from the ventricle with each beat = end diastolic volume - end systolic volume. Normally ~80ml
Ejection fraction
stroke volume/end diastolic volume. Normally 0.4-0.6
Cardiac Output
stroke volume x heart rate. Normal value ~5 L/min
Why is stroke volume not decreased when diastolic time is decreased?
Because of the rapid filling phase
What is the difference in pressures developed in right vs. left side of heart?
much lower pressures developed in the right ventricle and pulmonary artery as compared to left ventricle and aorta, respectively
Where can the venous pulse be felt?
jugular vein
What does the venous pulse approximate?
atrial pressure curve
How does the right ventricle cause ejection?
During ejection a slight movement of the wall of the right ventricle towards the septum produces a large decrease in ventricular volume. This is further aided by the bulging of the septum towards the right ventricular chamber due to the contraction of the left ventricle.
What are the right ventricle muscular fibers like?
In the right ventricle the fibers run mostly in the longitudinal (base to apex) direction. This does not allow for much change in thickness
What are the left ventricular fibers like?
powerful layer of circular muscle whose contraction is the main pressure generator during systole
What is responsible for the 1st heart sound?
Closing of the mitral and tricuspid valves.
Is S1 normally split?
No, because mitral and tricuspid valves close simultaneously
What is responsible for the 2nd heart sound?
Closing of pulmonary and aortic valves
Is S2 normally split?
Yes because the pulmonic valve closes slightly after the aortic valve
What causes trailing off of 1st heart sound (murmor)
Turbulent flow in the root of the aorta during rapid ejection
Laplace's law
the total force that tends to stretch the ventricle is equal to the ventricular wall forces that oppose the stretch
Pπr^2 = 2σπrd
What is the relationship between mural stress of the ventricular wall and the radius of the ventricular chamber
Proportional
What is the relationship between mural stress of the ventricular wall and the thickness of the ventricular chamber
Inverse
Why does ventricular wall thickness increase when under chronic pressure or volume overload
To reduce stress via the thickness vs. mural stress inverse relationship
What happens in pressure overload hypertrophy
Increase in mural wall thickness because mural stress can be reduced by increased thickness
What happens during volume overload hypertrophy?
Increase in mural wall thickness and ventricular chamber radius
What are the stages in the cardiac cycle
1. Slow filling (diastasis)
2. Isovolumetric contraction
3. Ejection Phase
4. Isovolumetric relaxation
5. V-Rapid filling
Which is the longest phase in the cardiac cycle?
Diastasis (slow-filling)
When does slow filling occur
After they are 2/3 full from rapid filling
What is happening to aortic pressure during diastasis?
Dropping to EDP as blood flows into the peripheral and coronary arteries
What is happening to ventricular volume during diastasis?
1/3 of end-diastolic volume is added. At end of diastasis, atrial systole adds a small volume (atrial kick)
Which valves are open/closed during diastasis?
Mitral valve is open
Aortic valve is closed
What is happening to atrial pressure during diastasis?
It's increasing to its maximum value, remaining above ventricular pressure
What heart sound is heard during diastasis?
The patient may or may not have a 4th heart sound
When is the 4th heart sound heard?
During diastasis
What is happening to ventricular pressure during isovolumetric contraction?
Rising rapidly towards EDP
What is happening to aortic pressure during isovolumetric contraction?
Falls to EDP due to continued efflux of blod to periphery
What happens to ventricular volume during isovolumetric contraction?
No change!!
What happens to atrial pressure during isovolumetric contraction?
There is a brief pressure wave due to mitral valve leaflets bulging into the atrial when ventricular pressure increases. This increases the atrial pressure initially. But then the chorda tendenae pull the valve towards the ventricle. This increases the atrial chamber size and decreasing its pressure, favoring refilling of the atria
When is the 1st heart sound heard?
During isovolumetric contraction
What causes the 1st heart sound?
Due to vibrations form A-V valve closure
What is the ECG like during isovolumetric contraction?
QRS complex
Which valves are open/closed during isovolumetric contraction?
All closed
What happens to ventricular pressure during the ejection phase?
When ventricular pressure is greater than aortic pressure, the aortic valve opens. Ventricular pressure continues to rise though in order to stay above aortic pressure (and keep flow going). It peaks and then starts dropping until it drops lower than the aortic pressure. Blood continues to flow into the aorta despite unfavorable pressure gradient because of the inertial momentum of the blood flow
What happens to aortic pressure during the ejection phase?
Following ventricular pressure basically
What happens to ventricular volume during the ejection phase?
Decreases rapidly during rapid ejection and then slows down when ejection slows (during the momentum-mediated phase of ejection)
What happens to atrial pressure during the ejection phase?
Decreases rapidly (atrium gets stretched towards apex by ventricular contraction) but then increases slowly as atrium fills
What heart sounds are heard during the ejection phase?
None!
What is the ECG like during ejection fraction?
Right after QRS until end of T. T = period of reduced ejection
Which valves are open/closed during ejection fraction?
Aortic valve is open
Mitral valve is closed
What valve opens at the end of isovolumetric relaxation?
Mitral valve
What happens to ventricular pressure during isovolumetric relaxation?
Drops quickly
What happens to aortic pressure during isovolumetric relaxation?
Small pressure wave from aortic valve closing and blood rebounding off as flow reverses. Pressure then falls as blood flow to periphery
What happens to ventricular volume during isovolumetric relaxation?
No change!
What happens to atrial pressure during isovolumetric relaxation?
Slowly rises as the atria fill
Which heart sound is heard during isovolumetric relaxation?
S2
What causes S2?
Vibrations from aortic/pulmonary valves closing. It's a high frequency, lower intensity and shorter duration than 1st sound
What happens on the ECG during isovolumetric relaxation?
Baseline
Which valves are open/closed during isovolumetric relaxation?
All are closed
What happens to ventricular pressure during v-rapid filling?
Decreases as ventricular muscle continues to relax
What happens to aortic pressure during v-rapid falling?
Continues to fall as the aorta empties
What happens to ventricular volume during v-rapid filling?
Rises rapidly to 2/3 of EDV
What happens to atrial pressure during v-rapid filling?
Falls as blood flows into ventricles. Remains above ventricular pressure to force blood.
What heart sound can be heard during v-rapid filling?
Can sometimes hear a 3rd heart sound in apex. Vibrations of ventricular wall due to sudden deceleration of blood flowing into ventricles at end of filling
What happens on the ECG during v-rapid filling
baseline
What is the state of valves during v-rapid filling?
Mitral valve open
Aortic valve closed