Echo physics Flashcards
What is the other name for frank-starling principle?
Length tension relationship
What is the frank-starling principle? 3
- The degree of stretch of the cells in the ventricular wall is determined by the volume of blood within the chamber
- Force of contraction is greater when the LV muscle is stretched prior to contraction by increased preload
- More blood to the heart (preload), greater tension, greater force generated during systole»_space;> greater SV
According to the Frank starling law, the normal heart adapts to different preloads how?
By pumping the volume of blood delivered to it
According to the frank starling law, a increase of blood entering the heart results in what?
Increase in the force of contraction
this is due to greater stretch of the myocardial muscle fibers, similar to a elastic band
What is stroke volume?
The amount of blood ejected with each beat of the heart
What are the two ways Stroke volume can be calculated?
- 2D
- Doppler
What is the 2D calculation of Stroke volume?
SV = EDV - ESV
What is the doppler calculation for stroke volume?
SV = CSA X VTI
(cross sectional area x Velocity time integral)
What is the normal stroke volume at rest?
50-100ml/beat
IF we know the SV and the heart rate, we can figure out what in terms of Stroke volume/ Cardiac output?
How much blood is pumped out of the heart in one minute
What is Cardiac output?
The amount of blood pumped out of the heart in one minute
What is the cardiac output formula?
CO = SV X HR
What is the Normal CO
4-6 L/min
What is cardiac index?
The cardiac output indexed to accommodate for body surface area
Is Cardiac index normally used?
Less commonly
What is the formula for cardiac index?
CI = CO/BSA
What is chronotropic force?
Heart rate
Based on the Cardiac output formula, more beats per minute would affect cardiac output how?
Increase our cardiac output
What does the sympathetic nervous system do?
Increases chronotropic force (and inotropic force)
When would the Sympathetic nervous system Increase chronotropic force? 3
- Times of stress
- Physical (exercise, fever)
- Emotional (fear, worry, anxiety, anger, excitement, frustration)
If SNS increases what happens to HR?
It would increase
What does the parasympathetic nervous system do?
Decreases chronotropic force
How does the parasympathetic nervous system decrease chronotropic force? 4
- Rest
- Beta blockers/ calcium channel blocker medications
- Being fit
- Meditation / relaxation techniques
If PNS increases what happens to HR?
It decreases
What is preload?
The amount of blood in the ventricle at end diastole. The volume load delivered to the ventricle
What is the formula for preload?
Increase in preload = Increase EDV/SV/CO
What factors directly affects preload? 2
- Filling time
- Venous return
What directly affects venous return for preload?
Blood volume and venous pressure
What inversely affects venous return for preload?
Intrathoracic pressure
The longest phase of the cardiac cycle is what?
Diastole: the filling phase
When the heart rate increases there is what? 3
- Less time for ventricular filling
- Decrease in preload
- Decrease in stroke volume (as a result of decreased preload)
If HR increases what happens to stroke volume?
It decreases
*when no other factors are applied to the SV, such as during tachycardia)
What happens in terms of diastole time, filling time, and preload when there is an decrease in heart rate?
- Increase diastole time
- Increase filling time
- Increase preload
What happens in terms of diastole time, filling time, and preload when there is a increase in heart rate?
- Decrease in diastole time
- Decrease in filling time
- Decrease in preload
When there is an increase in venous return what happens to preload?
It also increases
extra blood entering RA continues on to enter LV
Why would increase in blood volume increase venous return?
More blood in the entire system means more blood filling LV
Why would an increase in venous pressure increase venous return?
Blood naturally moves from higher to lower pressure
Why would decrease in intrathoracic pressure increase venous return? 2
- During inhalation diaphragm moves down, which results in less pressure in the thoracic cavity.
- Since there is higher pressure in Abd veins blood moves towards the heart.
inspiration does what to venous return?
Increase Venous return to the right heart
What does expiration do to the Venous return of the heart?
Decrease VR to the right heart
What does standing do to Venous return?
Decreases because gravity pulls blood down towards your legs
What does squatting do to venous return?
It increases venous return, because squats squeeze blood in veins towards the heart
What does the valsalva maneuver do to venous return and stroke volumes?
It decreases venous return and stroke volume. This is because valsalva increase intrathoracic pressure
What is afterload?
Resistance to ventricular emptying
Increase to afterload does what to stroke volume and cardiac output?
Increase in Afterload = Decrease in Stroke volume and Cardiac output
What affects afterload? 4
- Hypertension
- Viscosity of blood
- Valvular stenosis
- Vascular geometry
What does hypertension from after load lead to?
Enlarged Left heart muscle
What are other names for contractibility? 2
- Inotropic force
- Force velocity relationship
Contractibility is the force of what?
Contraction at a given preload and afterload
Contractibility is not related to what?
Frank starling mechanism
An increase in the force of contraction affects stroke volume how?
It increases it
SNS does what to contractility?
It increases it
What are negative inotropic responses? 2
- Structural disorganization (disease) = hypoxic, ischemic, infarcted, fibrosed or infiltrated muscle tissue
- LV cannot contract enough
What is positive inotropic response?
- Medications can make it easier for the heart to contract altering the sympathetic nervous system
How does Exercise increase cardiac output and stroke volume?
During exercise, inotropic force is the greater variable, and the SV and CO increase
What is the Continuity principle?
Flow rate at any given point must remain constant
So how would we apply the continuity principle to a narrowing in a blood vessel?
Velocities at a narrowing are greater than the velocities before and after the narrowing. (The blood speeds up through then returns to normal)
So how do we translate flow rate to flow rate in terms of the continuity principle?
- Stroke volume must remain constant at any two parts in the heart
- All four valves should have the same SV in the absence of a shunt or regurgitation
The stroke volume through any valve in the heart can be calculated using what?
CSA of the valve annulus and the PW VTI of the flow through the valve
What is the formula for CSA?
CSA = 0.785 x diameter^2
What measurements do we take for the continuity principle and AVA? 3
- LVOTd
- AV trace (spectral)
- LVOT trace (spectral)
What is the formula for AVA?
