3.2.2. Hemodynamics Flashcards
How does pressure relate to flow and resistance?
Delta P = Q x R
How does pulmonary resistance compare to that of peripheral resistance?
Pulmonary resistance is a lot lower than peripheral resistance.
What is 1 Peripheral Resistance Unit (PRU)
mmHg/(ml/sec)
How does flow relate to the radius of the vessel?
Q̇ α r4; the radius makes a huge difference in regard to flow
How does flow relate to vessel length?
Q̇ α 1/L
What is Poiseuille’s Law
Q̇ = kr4ΔP/L
What are 4 assumptions of Poiseuille’s Law?
- Flow is laminar
- Flow is through smooth cylindrical rigid tubes
- Velocity does not change
- Viscosity of the fluid is constant
In a vessel, where is the velocity the fastest?
The center.
How would you determine turbulent flow?
Depends on: radius of tube, density and viscosity of fluid
The mean velocity are combined into a dimensionless Reynolds Number (Re)
Allows you to estimate conditions producing turbulent flow
Re = 2r⊽ρ/η
⊽ = mean velocity
η = viscosity
If Re > 2000, turbulence is probable
Why is turbulent flow bad for the heart?
Wastes energy and makes the heart work harder for the same flow.
What qualities of a vessel contradict the assumption that blood flows through smooth cylindrical rigid tubes?
- Arterial plaques disrupt smooth arterial walls
- Diameter changes between diastole and systole
- Vessel diameter changes with pressure
- Branching
What is compliance? Formula?
A property of blood vessel undergoing a change in volume when subjected to an applied pressure.
C = ΔV/ΔP
How does compliance compare among arteries and veins?
The compliance of a systemic vein is ~24 times that of its corresponding artery
How does calcification affect vessel compliance?
Calcification increases wall stiffness and decreases vessel compliance.
How does the sympathetic activity affect compliance?
Stimulation causes decreased compliance. Inhibition causes increased compliance.
How does compliance change with age?
With age, compliance begins to decrease in the normal range of blood pressures
The heart is unable to eject its stroke volume as rapidly into the rigid vascular system.
How does compliance relate to elastance?
Elastance = 1/Compliance
When are Poiseuille’s assumptions better?
As you move further from the heart.
What is a Newtonian fluid?
A fluid with a viscosity that is independent of the forces on it and the velocity of flow. Blood is a Newtonian fluid.
At constant P, L and r, how does viscosity affect flow?
Increases in viscosity decrease flow
The kidneys and GI tract are examples of resistances in…
Series
The cardiovascular system is an example of resistances in …
Parallel
Adding a resistor to resistance in series increases or decreases the total resistance?
Increases.
Adding a resistor to resistance in parallel increases or decreases the total resistance?
Decreases
