Cardiac Function Curves + Pressure-Volume Loops Quiz 6. Flashcards
What does the Pressure-Volume Loop Tell us?
It shows the pressure-volume relationship in the left ventricle during one cardiac cycle - one systole and one diastole. It provides an assessment of the systolic and diastolic functions as well as the integrity of the cardiac valves. It does not measure heart rate or linear time.
What are the 3 functions of veins?
- Conduits for return of blood to the heart
- Reservoir for the cardiovascular system (70% of total blood volume)
- Maintain cardiovascular stability through changes in capacitance (through sympathetic-mediated smooth muscle tone)
What is venous return?
The amount of blood returned back to the right atrium via the venous system over the course of a minute.
What is the cardiac function curve?
Frank Starling Curve
It demonstrates the Frank-Starling Relationship.
How do venous compliance changes affect the venous return curve?
Increasing resistance to venous return decreases the slope of the venous return curve.
How does Contractility affect Cardiac Function Curve?
↑Contractility = Up and Left
↓Contractility = Down and Right
What is the venous return curve?
describes the inverse relationship between venous pressure and cardiac output
How does afterload affect Cardiac Function Curve?
↑Afterload = Down and Right
↓Afterload = Up and Left
Why does the venous return curve plateau as RA pressure becomes negative?
At negative RAP, veins collapse as they enter thorax and restricts venous return
How do blood volume changes affect Venous Return Curve?
↑TBV =
↑Venous Return
↑RAP
↑MCFP
How do venous compliance changes affect Venous Return Curve?
↓Compliance =
↑Venous Return
↑RAP
↑MCFP
Mean Circulatory Filling Pressure
Circulatory Pressure when heart is stopped and there is no flow
Arterial Pressure falls & Venous Pressures rise until equal
MCFP = 8 mmHg
What factors affect MCFP?
TBV & Compliance
Venous Compliance will have most impact
Does CO = Venous Return?
It should according to Frank Starling
What is thought to be the mechanism behind Frank Starling Relationship?
Optimization of Myosin & Actin - more Ca+ to bind to cardiac muscles
Factors that Effect Cardiac Function Curve
Afterload & Contractility
Blood Reservoirs (6)
Spleen
Liver
Large Abdominal Veins
Venous Plexus under Skin
Heart & Lungs
What is Unstressed Volume?
Amt of blood in the vein before pressure is generated
When are different Venous Curves parallel?
Changes in Blood Volume or Venous Compliance
How do resistance changes effect Venous Return Curve?
↑SVR = Down and Left
↓SVR = Up and Right
No MCFP Change
Curves Unparallel
Are pressure generated loops made in a counterclockwise fasion?
Yes
What is the point of Intercept between the Starling Curve and Venous Return Curve?
Equilibrium point where
Cardiac Output = Venous Return
What happens to the Starling Curve & Venous Return curve during exercise?
Sympathetic stimulation & Small ↑CO & Venous Return
then
Big ↑CO, Venous Return, MCFP
What is the Y-axis on Pressure-Volume Loop
Pressure
What is the X-axis on the Pressure Volume Loop
Volume
What is time’s role in Pressure Volume Loops?
Time plays no role
List 1-4
1: Filling
2: Isovolumic Contraction
3: Ejection
4: Isovolumic Relaxation
List 1-4
1: Mitral Valve Open
2: Mitral Valve Close
3: Aortic Valve Open
4: Aortic Valve Close
List 1-2
1: End-Diastole
2: End-Systole
What is the Red Line?
End-Systolic Pressure-Volume Relationship
(ESPVR)
End Systolic Pressure Volume Relationship Changes
Change of Intercept Point = ΔAfterload
Change in Slope = ΔContractility
What is this showing?
End-Diastolic Pressure-Volume Relationship
Ventricular Compliance
Red line indicates stiff ventricle & higher filling pressure
Whats happening here?
Increased Afterload
⬇️ cardiac muscle shortening ⬇️ stroke volume (⬇️ chamber emptying and ⬆️ end-systolic volume).
The loop gets narrower, taller and shifts the ESV to the right.
Whats happening Here?
Increased Contractility
⬆️ cardiac muscle shortening
⬆️ stroke volume (⬆️ chamber emptying > ⬇️ end-systolic volume).
The loop gets wider, taller and shifts to the left.
Whats happening here?
Increased Preload
(⬆️ End-diastolic volume)
⬆️ Cardiac Muscle shortening and ⬆️ Stroke volume
The loop gets wider but returns to the orginal end-systolic volume.
How are changes in stroke volume demonstrated by a pressure-volume loop?
SV = EDV - ESV
The width of the loop represents the difference between EDV and ESV, which is SV.
