Hemodynamics Flashcards
Factors that affect Blood flow volume?
Pressure Gradient, Tube Radius, Tube Length, & Blood Viscosity
The factors that affect Blood flow volume are expressed how?
Poiseuille’s Law
Poiseuille’s Law
States that flow volume varies directly with the pressure gradient and the 4th power of the radius of the tube, & flow varies inversely with the length of the tube & viscosity of the fluid
As pressure gradient increases
flow volume increases
As tube diameter or radius increases
flow volume increases
As length of the tube increases
flow volume decreases
As fluid viscosity increases
flow volume decreases
What has the greatest effect or influence on the flow volume and flow resistance?
Tube diameter or radius, because it is to the 4th power
What will increase resistance of flow?
An increase in Fluid viscosity and or tube length
What determines how blood moves in the heart?
Blood moves from an area of high pressure to area of low pressure
Average pressures in each chamber(diastole/systole)
RA:5/5, RV:5/25,
LA:10/10, LV:10/120,
PA:10/25, AO:80/120
Pressure Gradient
Difference in pressure on either side of a valve
Describe the normal PG between atria & ventricle during diastole? During systole?
Low PG during diastole.
High PG during systole.
Describe the normal PG between great arteries and ventricles during systole? During diastole?
Low PG during systole.
High PG during diastole.
What does low PG do?
Allow blood flow
What does high PG do?
Keeps valves shut
Five types of steady flow?
Inlet(Plug), Laminar, Parabolic, Disturbed, Turbulent
What is Inlet(plug) flow?
All velocities are equal at all radical distances from the center of the tube. usually located at the entrance of a great vessel(AOV or PV)
What is Laminar flow?
When fluid particle motion becomes smooth and parallel to each other. Fully developed laminar flow becomes parabolic in shape.
What is Disturbed flow?
Occurs at an area of stenosis or vessel bifurcation where fluid particles still flow in a forward direction but have been disturbed
What are the types of laminar flow?
Inlet(plug), parabolic, and disturbed flow
What is Turbulent flow?
Occurs when fluid particles move in multiple directions and different velocities and is considered abnormal flow. Turbulent flow net direction of flow is forward.
What is a Vortices?
Fluid with whirling or circular motion and may develop where blood becomes turbulent
What is a Eddi flow?
small circular currents may develop where blood becomes turbulent
What predicts Turbulent flow?
Reynolds number greater than 2000
When turbulent flow is present what happens to the PG?
It increases rapidly
Bernoulli equation states what?
There will be an increase in velocity(kinetic energy) with a decrease in pressure(potential energy) at the site of an obstruction to flow. An inverse relationship
Bernoulli based on what?
Conservation of energy principle which says that if there is a change in one of these energies, potential(pressure), kinetic(velolcity), or gravitational energy there will be a change in the other energies to maintain the same level of total energy.
Simplified Bernoulli equation?
P=4(Vsquared)
In clinical imaging ultrasound
proximal velocity, flow acceleration and viscous friction are ignored
Pitfalls of Bernoulli equation?
- If proximal velocity is greater than 1.0m/s (PG may be overestimated)
- Stenosis in a series (coronary artery disease, or tunnel like stenosis (coarctation,prosthetic heart valves),=PG will be too low due to ignoring viscous friction
Why do you estimate PG from transvalvular velocity?
To assess severity of stenosis
Echo is?
Non-invasive, low risk, reproducible, lower cost than heart cath and the method of choice in evaluation of valvular heart diseases
Heart Catherization
Gold Standard
Valvular Stenosis
Causes a reduced orifice
How do we evaluate valvular stenosis?
2D, color flow, and spectral doppler
Valvular Stenosis causes a pressure overload where?
Chamber proximal to the obstruction and turbulent flow distal to it.
AS/PS Where does pressure increase?
Ventricles
MS/TS Where does pressure increase?
Atrias
AS/PS What is the effect on velocity through the valve?
Increases with abnormal flow, and will have lower pressure
AS/PS What is the effect on the chamber?
Hypertrophy, enlarged & thickened like a larger muscle, pressure has increased with the abnormal flow, and will have a lower velocity
MS/TS What is effect on the velocity through the valve?
Increases with abnormal flow, will have lower pressure
MS/TS What is the effect on the chamber?
Atria dilate and stretch (like a balloon) because of increased pressure. Pressure lowers at stenosis, and normalizes distal to stenosis
Which part of the stenosis is the velocity the highest?
The narrowest part of the stenosis, pressure lower
Which part of the stenosis is the pressure the highest?
Proximal to the stenosis
With regurgitation, the abnormal flow (turbulent flow) results will be?
Volume overload, chamber dilation, can have pressure overload and volume overload together
