Hemodynamics Flashcards
What is hemodynamics? What else does it refer to?
Study of blood flow in the circulatory system and refers to both power and blood
The circulatory is a closed circuit system that comprised of what? 4
- Heart
- Arteries,
- Capillaries
- Veins
Contracting muscles in the circulatory do what?
Act as the pump to get the blood back to the heart, sometimes called the venous heart
In the study of blood flow it is helpful to understand what? 3 (make up)
- Plasma consists (water and protein) of 55%
- Erythrocytes consists (RBC) of 45%
- Leukocytes and platelets <1%
What is hematocrit?
Perectage of blood that is red blood cell. Defined as the mass per unit volume or the resistance of an object to accelerate.
How much of the blood volume is referred to as hematocrits?
45%
In terms of hematocrits what is viscosity? What does this mean for velocity?
- Resistance to flow.
- The more viscous the blood the slower the velocity
The greatest amount of blood is where?
In the veins, it accounts for about 65%
Capillaries have an area of what? Compared to other vessels?
600-100X
What is the volume and velocity in the capillaries?
Relatively low
What do we need for any fluid to flow?
A pressure difference
How can a pressure difference be made created in the body?
Heart or gravity
For hemodynamics, an increase in pressure results in what?
Increased flow rate
Blood flowing in a vessel is synonymous with what?
Current flowing through a wire
What is the formula for ohm’s law?
Current = voltage/ resistance
In the body, the voltage is what?
The pressure gradient
What is the current in terms of hemodynamics?
Volume flow rate
What is pressure gradient?
The pressure difference divided by the distance between two pressure locations
What is the pressure gradient formula?
P gradient = (p1-p2)/L
What is volume flow rate (Q)?
The volume of blood passing a point per unit time
The total adult blood flow rate is what?
~ 5000 ml/min and is called the cardiac output
What is poiseuilles law for resistance? (Formula)
R = (8 x length x viscosity/ pie x radius^4)
What is poiseuilles law work on
Straight tubes only
When blood flows through vessels it can have different flow patterns depending on what? 4
- Diameter
- Tortuously
- Bifurcations
- Anastomoses
What are the different types of flow patterns 5
- Plug
- Laminar (parabolic)
- Jet
- Disturbed
- Turbulent
What is plug flow?
Seen at the opening of large vessels like the aorta and has almost all RBCs travelling at the same velocity
What is laminar parabolic flow?
The RBC’s move in concentric layers with the ones in the Center moving faster than the ones near the wall.
What is the most common of flow pattern in the body
Laminar parabolic flow
What is Jet Flow?
The velocities within narrow openings are much faster then the rest
Where do we see Jet flow?
When there is a significant reduction in the diameter of a vessel
What is disturbed flow?
Occur naturally in the presences of vessels tapering, curvatures, bifurcations. Similar to laminar but not straight and has many different variations
Where is an example of disturbed flow location?
Carotid bulbs
What is turbulent flow?
Flow velocities are greatly varied as are flow directions and can be described as chaotic.
Where do we usually see turbulent flow?
Past a stenosis, and is unusual in the body except in and near the heart
What is Reynolds’s number (RN)?
Can predict the onset of turbulence in a vessel and is calculated from the following formula. 2000.
What happens if RN is above 2000
Turbulence results
What is the continuity rule?
In the presence of a stenosis the volume of flow must remain constant proximal to, at and distal to the stenosis
How do we achieve the continuity rule?
The velocity of blood increases in a stenosis to keep the volume flow constant
If the diameter of the stenosis is 1/2 of the normal vessel then what happens?
Velocity is doubled through stenosis to maintain the volume flow
Bernoulli’s principles establishing a relationship between what?
Kinetic energy, gravitational potential energy and pressure in a frictionless fluid system
How does Bernoulli’s system affect flow rate?
The volume rate is maintained and the energy within a fluid system is kept in balance as well
Total fluid energy (E) is comprised of what?
Both potential energy and kinetic energy
Potential energy is what in terms of Bernoulli’s principles?
The intramuscular pressure plus the gravitational potential energy
In terms of Bernoulli’s principle pressure is produced by what? 3
- The contraction of the heart
- The hydrostatic pressure
- The static filling pressure
At the stenosis there is what? And why is it necessary?
There is a pressure drop which is necessary for the fluid to accelerate through the stenosis and decelerate past the stenosis
Pressure or potential energy is converted to what?
Kinetic energy (flow) on entry and back to pressure energy on exit
The drop in pressure, in a stenosis, can be what?
Calculated using velocity of blood flow in the Jet with its simplified formula
What is the formula for bernoullis principle
P = 4(V2)^2
The velocity before the stenosis is small compared to what?
Jet and can be ignored
Where do we use bernoullis Principle formula?
Echo for stenoitic heart valve
What is tarsus parvus?
After a stenosis there is a drop in the acceleration time and peak systolic velocity of arterial flow
What is the Windkessel Effect?
The windkessel effect is the continued forward flow in the aorta during diastole as a result of the elasticity of the vessel walls contracting back to their original diameter
During the Windkessel effect, the flow can’t reverse back to the heart because of what?
The aortic valve has closed
The pressure wave along the walls of the vessel travels what?
Faster then the blood travelling within
When the wave reaches the end of the arterial system what happens?
There is a reflected wave that causes the vessel wall to expand and contract against the flow of blood
If there is a increased pressure down stream and the heart is in diastole what happens?
Blood is reversed back towards the heart
What part of the body is known as the venous heart?
Calf muscles
The pressure wave velocity and blood flow velocity are related how?
Inversely
