20 - Hemodynamics Flashcards
What is laminar blood flow?
- It is blood flow characterized by layering
- The layer at the center of the blood flow travels the fastest
- The layers on the walls of the vessels flow the slowest (kind of sticks to the walls)
What does laminar blood flow provide?
The maximum amount of flow for a given pressure
What is the difference between laminar blood flow and turbulent blood flow?
Laminar blood flow has a parabolic velocity profile while turbulent flow is disarrayed with a squared velocity front
Can turbulent flow be heard with a stethoscope?
Yes
Can laminar flow be heard with a stethoscope?
No
Laminar pressure requires ______ pressure than turbulent flow in order to move
Less
What are Korotkoff sounds?
Korotkoff sounds are sounds that are produced by inducing turbulent flow in a blood vessel in order to measure blood pressure
Describe how Korotkoff sounds are used to measure atrial blood pressure (systolic pressure)
- A blood pressure cuff is inflated PAST the systolic pressure
- This stops blood through the vessel
- As the pressure is slowly released, the blood will rush through the vessel and crash into the blood ahead of it
- This creates turbulent noise that can be heard
- The pressure at which this is first audible is the systolic pressure
Describe how Korotkoff sounds are used to measure atrial blood pressure (diastolic pressure)
- As the pressure is further decreased, turbulence becomes less as the vessel diameter returns to normal
- The turbulent flow soon stops as does the noise
- This point is the diastolic pressure
How does velocity of blood flow affect the tendency of turbulent blood flow?
Increasing velocity increases the tendency of turbulent blood flow
How does the diameter of the vessel affect the tendency of turbulent blood flow?
Increasing the diameter of the vessel increases turbulence
How does the viscosity of the blood affect the tendency of turbulent blood flow?
Increasing the viscosity decreases the tendency toward turbulence
What is hematocrit?
The volume percentage of red blood cells in blood. It is normally 45% for men and 40% for women.
How does the hematocrit affect the viscosity of the blood?
As the hematocrit increases, so does the viscosity of the blood
How is laminar flow characterized by these features of blood flow?
- High viscosity
- Low density
- Small diameter
- Low velocity
What is anomalous viscosity?
As blood flow decreases, viscosity increases
Is this normally a concern for a healthy adult?
No, because flow remains relatively constant
How would this affect a person in shock?
A person in shock is more susceptible to this, so an abnormally high hematocrit is one explanation as the RBCs are concentrated in less plasma
The blood is “thicker”
What is the relationship between the tension in the wall of a blood vessel to the radius and pressure of that blood vessel?
The tension in the wall is proportional to the radius
If the radius is increased, so is the tension in the wall of the vessel
Is this the same for chamber tension and radius and pressure?
Yes - same relationships as seen in vessels
What is the law of LaPlace?
The law states that the tension of a capillary is directly related to the radius, so the small the radius, the less the tension
What does this mean in terms of the structure and function of capillaries?
This law explains the mechanism by which capillaries are able to hold high pressure without having muscular walls
How does the law of LaPlace help to predict the outcome of aneurysms?
We know that as the radius of a vessel increases, so does the tension on its walls
The larger the aneurysm, the more tension is being placed on its walls, and the greater chance that it will rupture
What percentage of blood is in the venous circuit at any given time?
75% of total blood volume
What percentage of blood is in the arterial circuit at any given time?
20% of total blood volume
What percentage of blood is in the capillaries and post capillary venules at any given time?
5% of total blood volume
Where does the flow of blood begin in the vascular system?
The aorta
What happens after the blood enters the aorta?
It is progressively subdivided to the greatest possible number of divisions and eventually enters the capillaries
Does flow remain the same or decrease throughout all of these divisions?
Flow remains the same
What is the flow velocity most dependent upon?
The radius of the vessel
How does the radius effect flow velocity?
Exponentially (to the fourth)
What happens to the flow velocity when the radius of the vessel doubles?
The velocity of the flow increases by 16 times
What happens to the flow velocity when the radius of the vessel is cut in half?
The velocity of the flow will be 1/16 of the initial velocity
What happens as the surface area increases?
Velocity decreases
Why do we see a decrease in velocity when surface area increases?
The same amount of blood is moving through more vessels
What does the surface area consist of?
All the vessels the blood is flowing through
The surface area increases with each division on the arterial side and decreases with subsequent divisions of the venous side
Through which vessels is the surface area increasing?
Aorta –> arteries –> arterioles –> capillaries
Through which vessels is the surface area decreasing?
Capillaries –> venules –> veins –> vena cava
What is the equation for calculating flow?
Flow is equal to the (pressure going into the system - pressure going out of the system) divided by resistance
Flow = (Pi-Po)/Resistance
What information do you need to know to calculate the total peripheral resistance?
TPR
- Inlet pressure (Pi)
- Outlet pressure (Po)
- Cardiac output
What information do you need to know in order to calculate the pulmonary circuit resistance?
PCR
- Pressure of pulmonary artery (inlet)
- Left atrial pressure (outlet)
- Cardiac output
Why is the resistance and pressure of the pulmonary circulation much lower than the systemic circulation?
Because the blood vessels are much shorter
How do we use Poisseulle’s law to determine this?
According to Poisseulle’s law, the flow is inversely proportional to resistance
The short length of the vessel means that the resistance
How do we define resistance?
8nL / (pi)r4
n = viscosity L = length of the vessel r = radius
