Fluid Dynamics Part 1 Flashcards
What are arteries characteristics?
Oxygenated blood to tissues High pressure Start at heart and ends at periphery and organs Thick walled Aorta – largest Driven by the heart
What are veins characteristics?
Return deoxygenated blood to heart Low pressure Start at periphery and ends at right atrium of heart Thin walls IVC – largest Driven by respiration and muscles
What do pulmonary arteries do?
Only pulmonary arteries transport unoxygenated blood from the heart to the lungs
Other characteristics of arteries?
Firm, Non-compressible walls
Pulsatile waveforms
Have differences in resistance of waveforms in different parts of the body
Deliver oxygenated blood from the heart to the rest of the body
Only pulmonary arteries transport unoxygenated blood from the heart to the lungs
Driven by the heart as a pump
High pressure system
What are the three layers of arteries?
intima, media, adventitia
Describe circulation
Increased pressure in LT Ventricle
Aortic valve opens
Blood ejects from LT Ventricle
Waves of energy pass through the vessels
These waves are continuous with the beating of the heart
The arteries hold a reservoir of blood as the energy increases and decreases
What is energy gradiant?
When there is a difference in total fluid energy from one location to another blood will flow
What are forms of energy?
Kinetic
Pressure
Gravitational
What happens when there is a change of energy?
If there is a change in one type of energy the others must change to conserve the total amount of energy
What is pressure energy?
Potential energy
Ability to do work
Pressure in a vessel helps blood to overcome resistance and continue to flow
What is kinetic energy?
Moving objects Depends on Mass of object Speed of object Thus heavy objects with high velocity have more kinetic energy than lighter objects with slow velocity
What is gravitational energy?
Stored or potential energy
Anything that is elevated as stored gravitational energy
Where does blood flow gets its energy from?
contractions of the heart
What are loses of energy?
Viscous Loss
Frictional Loss
Inertial Loss
What is viscosity?
Viscosity is the thickness of any fluid
Syrup has a high viscosity (thick)
Lemonade has a low viscosity (not thick)
What happens to higher viscosity?
the more energy lost
What measures percentage of red blood cells in the blood?
hematocrit
What happens if the hematocrit is low?
If hematocrit is low than the blood has a reduction in viscosity.
What is frictional energy loss?
One object rubs against another
Flow energy is converted to heat energy
What is an example of an frictional energy loss?
Example – blood rubs along the vessel walls causing a frictional energy loss.
What is inertial energy loss?
Inertia – resistance to change velocity
When an object changes its velocity it will lose energy
What are occurrences of inertial energy loss?
Pulsatile flow
Phasic flow
Velocity changes – caused by stenosis, high velocity at stenosis and a reduction in velocity after blood passes through the stenosis
What is hydrostatic pressure?
The weight of blood on the vessels (units of mmHg)
Changes depending on if it is above or below the heart
What happens to the hydrostatic pressure of a standing person?
When taking a person’s blood pressure who is sitting or standing needs to be at the level of the heart to be accurate
Pressures below the heart are too high
Pressures above the heart are too low
What happens to the hydrostatic pressure of a supine person?
When a patient is supine it is considered that all parts of the body are level with the heart and all pressures will be accurate
describe laminar flow
Normal physiologic states
Laminar literally means layered
Layers of blood flow, each traveling at their own individual speeds
What are two types of laminar flow?
Two types
Plug flow
Parabolic flow
Describe parabolic flow
Type of normal/laminar flow
Fluid layers slide over one another – bullet shaped
Occurs further from entrance of tube
Central portion of fluid moves at maximum speed
Flow near vessel wall hardly moves at all
friction with wall
Describe plug flow
Type of normal/laminar flow
Constant fluid speed across tube
Occurs near entrance of flow into tube
What is turbulent flow?
Random & chaotic
Individual particles flow in all directions
Streamlines disappear
What does turbulent flow occur?
Often occurs along with increased velocities beyond obstruction such as plaque on vessel wall causing a significant stenosis
Describe the sounds that can be heard with turbulent flow
Transfer of flow energy into sound and vibration – when heard this is called a murmur or a bruit
When tissue actually vibrates it is called a thrill – can be felt
Hemodynamic factors that affect how blood circulates:?
Pressure (ΔP)
Resistance (R)
Volume Flow (Q)
What if (Pressure Gradient)
Differing pressure (Pressure Gradient) within the vessel is the main force that drives circulation.
What is resistance based on?
Resistance within the vessels, based largely on vessel diameter, has profound impact on flow.
How are pressure and flow and resistance related?
directly
What are other factors that affect pressure other than flow?
η is viscosity
L is the length of the vessel
r is the radius of the vessel
R=8ηL/πr4
What affects resistance more than the other factors?
Diameter affects resistance more than viscosity or vessel length
How is radius and volume flow proportional?
Radius directly proportional to volume flow
What does conservation of energy say?
No matter what happens to radius flow must be maintained (conservation of energy)
Using poiseuilles law, what are the relationships for radius and flow and velocity?
Radius decreases / Flow volume decreases
To maintain flow velocity must increase
This relationship is seen in stenotic vessels
Describe poiseuille law relationships
Length of vessel increases, decrease in flow
Viscosity increases, decrease in flow
Radius of vessel increases, flow increases
What happens at a stenosis?
Narrowing in a vessel
Fluid must speed up in stenosis to maintain constant flow volume
no net gain or loss of flow
Turbulent flow common downstream of stenosis – post stenotic turbulence
Here a bruit may be heard from turbulent flow
What is Bernoulli principle?
Increase in velocity accompanied by decrease in pressure (Bernoulli)
Why does velocity increase at a stenosis?
At a stenosis velocity increases because the vessel tries to maintain the same flow volume
What is Reynolds number?
Predicts whether flow is laminar or turbulent
Flow is forward but chaotic
Reynold’s number for turbulent flow is greater than 2000
Dimensionless Re = Vavg x D x ρ/η
What happens at flow separation?
Areas of geometry change of the vessel
Fills in with color during systole
Either no, low flow or stagnant flow during diastole
Where do you see disturbed flow pattern?
Disrupted flow layers at:
Arterial bifurcations
CCA and bulb
With bernoulli principle what happens with velocity and pressure?
Increase in velocity (stenosis) is accompanied by a decrease in pressure
This comes from the law of conservation of energy
Example – we know the velocity increases at the site of a stenosis, therefore the pressure must be decreasing
What is the relationship between velocity and pressure?
inverse
What happens in the pre-stenosis?
proximal to stenosis Kinetic energy (velocity) low/pressure energy high
What happens at the stenosis with Bernoulli?
Pressure energy low/kinetic energy (velocity) high
What happens post stenosis?
distal to stenosis Kinetic energy (velocity) low/pressure energy high
