SM 111a - Pressure-Volume Loops and the Cardiac Cycle Flashcards
Which event of the cardiac cycle occurs at #4?
The mitral valve opens
Which law explains why LV thickening is an adaptation to chronic hypertension?
Laplace’s law
Thickening of the LV is a response to increased pressure that will keep the wall stress on each individual myocyte constant
Between which two numbers does isovolumic relaxation occur?
What is happening physiologically?
Betwen #3 and #4 (F and A)
The LV is in diastole. It is relaxing, but pressure has not yet fallen below LA pressure. Both the aortic and mitral valves are closed
During which phases is blood flowing from the right atrium to the right ventricle?
From the beginning of the y descent (marked by v) to the closure of the tricuspid valve (end of atrial systole)
Which curve represents heart failure?
2
Lower stroke volume at every end diastolic pressure
What is wall stress?
How is it calculated?
Wall stress is the circumfrential force per unit area that must be exerted to maintain a particular pressure inside the left ventricle
A myocyte will fail above a certain level of stress; therefore, thickening of the LV (increasing h) is an adaptive mechanism that decreases the stress on each individual myocyte
Which event of the cardiac cycle occurs at #3?
The aortic valve closes
What event happens at #1?
The mitral valve closes
What does the a wave represent?
Right atrial systole, latter part of ventricular filling
What event happens at #4?
The mitral valve opens
Between which numbers does isovolumic contraction occur?
What is happening physiologically?
Between #1 and #2 (C and D)
The left ventricle is in systole; it is contracting, but pressure in the LV has not yet overcome the aortic pressure. Both the mitral and aortic valves are closed
Which event of the cardiac cycle occurs at #1?
Mitral valve closes
What is the physiologic basis of a split S2?
When are we most likely to hear it?
Split S2 results when the aortic valve closes slightly before the pulmonary valve
We are most likely to hear it upon inspiration. Inspiration creates negative pressure in the lungs, futher decreasing the pressure in the pulmonary trunk (compared to pressure in the aorta)
What is Laplace’s Law?
Give the equation and explain
Laplace’s law gives the equation for wall stress
Wall stress is proportional to pressure and radius, and inversely proportional to the thickness of the wall (h)
This explains why LV hypertropy is an adaptive mechanism to chronic hypertension
At which number/letter would we hear S1?
1/C
The mitral valve closes
What does the v wave respresent?
Right atrial filling
Which event of the cardiac cycle occurs at #2?
The aortic valve opens
Isovolumic contraction happens between which two numbers?
1 and 2
When is the left ventricle in systole?
From just before #1 through just before #3
The mitral valve closes (#1) when the LV pressure becomes greater than the LA pressure, due to LV contraction (systole)
The aortic valve closes when the LV pressure drops below the aortic pressure, due to LV relaxation (diastole)
How does increasing preload affect the cardiac cycle?
Increased preload ->
- Increased LV end diastolic volume (actually, increasing EDV usually results in increased preload)
- Increased stroke volume
- May be a small increase in LV end diastolic pressure
At which number should we hear S1?
At which nubmer should we hear S2?
S1: At #1, when the mitral valve closes
S2: at #3, when the aortic valve closes
How does increasing contractility affect the cardiac cycle?
Increased contractility ->
- Increased maximum systolic pressure
- Longer ejection time
- Increased stroke volume
- Due to decreased end systolic volume (more blood is squeezed out)
- No change in end diastolic volume
Isovolumic relaxation happens between which two numbers?
3 and 4
What does the y descent represent?
The y descent begins wehn pressure in the RA exceeds that of the RV
The tricuspid valve opens, and blood flows from the RA to the RV. The y descent ends when the RA contracts to squeeze the last bit of blood into the RV
Which valves are open betwen D and F?
The aortic valve is open
The mitral valve is closed
Purple = normal pressure-volume loop
Which of the follwing changes created the red pressure-volume loop?
a) Increased contractility
b) Increased preload
c) Increased afterload
c) Increased afterload
What is the physologic basis of S1?
The tricuspid and bicuspid valves closing
What is the physiologic or pathologic basis of S3?
S3 occurs due to rapid deceleration of blood against a distended or incompliant left ventricle
This happens
Physiologic basis: Athletes and young children. Left ventricle fills almost to its maximum, and it cannot streth further to accomodate a “soft landing” of inflowing blood
Pathologic basis: Enlarged or weak heart
What value is represented by #5?
Stroke volume
Between which numbers/letters is the LV in systole?
Just before #1 (C) to just before #3 (F)
At which number/letter woudl we hear S2?
3/F
The aortic valve closes
When in the cardiac cycle are we likely to hear S4, if it is present?
Late in diastole, right before S1
What is the Frank-Starling relationship?
Increased myocyte stretch -> Stronger contraction
The LV pressure increase resulting from increased end diastolic volume and therefore increased preload, results in increased contractile force generated by the heart, and increased systolic blood pressure
Which valves are open between A and C?
The mitral valve is open
The aortic valve is closed
Purple = normal pressure-volume loop
Which of the follwing changes created the red pressure-volume loop?
a) Increased contractility
b) Increased preload
c) Increased afterload
b) Increased preload
When in the cardiac cycle are we likely to hear S3, if it is present?
Early in diastole, after the aortic and pulmonary valves close
Which curve represents increased intropy?
1
Increased intropy = increased contractility
Greater stroke volume for every end distolic volume
What event happens at #3?
The aortic valve closes
When is the left ventricle in diastole?
From just before #3 to just before #1
LV relaxation causes the aortic valve to close (3)
When it begins to contract at the end of systole, the mitral valve closes (1) in response
How does increasing afterload affect the cardiac cycle?
Increased afterload ->
- Increased maximum systolic pressure
- Decreased stroke volume
- Due to increased end systolic volume
- No change in end diastolic volume
Between which numbers/letters is the LV in diasole?
From just before #3 (F) to just before #1 (C)
What event happens at #2?
The aortic valve opens
What factors will increase myocardial O2 consumption?
Anything that causes the heart to work harder (ex: pumping more blood or overcoming some pathology), will increase myocardial O2 consumption
- Increased preload
- Increased afterload
- Increased contractility
- Increased HR
- Decreased pulmonary vascular resistance
- More return to LA, which goes to LV, which LV has to pump out
- Increased time in systole
What is the physiologic or pathologic basis of S4?
S4 is always pathologic
Occurs when forceful atrial contraction ejects blood into a stiff left ventricle
What does the x wave represent?
What interrupts the x wave?
The x wave represents relaxation of the atrium after atrial systole
It is interrupted by the c wave, when the tricuspid closes to create a brief pressure increase in right atrial pressure
Purple = normal pressure-volume loop
Which of the follwing changes created the red pressure-volume loop?
a) Increased contractility
b) Increased preload
c) Increased afterload
a) Increased contractility
What is the physiologic basis of S2?
The aortic and pulmonary valves closing
Note: it is normal for the aortic valve to close slightly beofore the pulmonary valve, causing a split S2
