Cardiac biophysics Flashcards
Blood is a _____ and ____ fluid
complex and incompressible
Pressure is a ____ force always present
compressive
Velocity is high in ____ vessels
large
Increase in volume increases the stress on the walls of a vessel which increases the ____
pressure.
Arterial pressure is _____ over the atmospheric pressure
120 mmHg
Total blood coming into a system must be ___ to the total blood coming out
equal
Flow rate (Q) formula
Q = Δ V / Δ t
Q = V x A
How would we find the Q?
V1 x A1 = V3 [A3 x n3]
When you increase the total cross sectional area what happens with velocity?
Velocity decreases
What happens with Q if the radius within the same system changes (eg: stenosis)
Q = V x A
Smaller radius = Higher velocity, to compensate and keep Q constant.
In a vertical tube with constant radius the velocity must be equal on the top and bottom. How is the Q maintain constant?
If kinetic energy is constant then the Q depends on the pressure and the potential energy.
(Bernoulli equation)
If potential energy is higher at the top then pressure must compensate, therefore pressure is greater on the bottom
What does the Bernoulli equation represent ?
The mechanical energy in a fluid
Bernoulli equation:
P + 1/2 ρ v2 + ρgh = cte in a fluid
1/2 ρ v2 = kinetic energy
ρgh = potential energy
If a radius is constant through out a horizontal tube then velocity is constant as well, what does this mean in terms of pressure?
If velocity is constant then acceleration is 0 so the total force must be 0. Making Pressure constant as well (P = F / A)
The bernoulli equation is not valid when ____ is present because ______ energy will decrease.
- friction
- mechanical
In a blood vessel, erythrocytes closest to the wall are ____ than those in the middle because of ___
slower
friction
Friction forces produce a ____ stress
shear
Shear stress appears in a blood vessel because
One layer of the fluid moves slower than the other pulling it back.
Shear stress in a fluid formula:
F / A = Δ V / Δ y x N
Δy = fluid layer separation
μ = viscosity
viscosity ( μ ) units
0.1 Pa x s = 1poise
What is the non-stop (no slip) condition ?
The molecules of the wall are so close to the fluid molecules that they assume the v = 0.
Almost as if the molecules closer to the wall are stuck to it
Wherever there is a velocity difference there is ____
friction.
As mechanical energy decreases what happens to the pressure within one tube with constant radius
Pressure decreases as well
What does this mean?
The velocity is greatest at the center and smallest close to the walls
Poiseuille’s flow
Δ P = ((8 μ L) / ( π r4 )) Q
Similar to electric V= IR
Hydraulic resistance
((8 μ L) / ( π r4 ))
If the radius increases what happens to the flow rate?
It increases too
If viscosity increases what happens to the flow rate?
It decreases
If the length of the pipe increase what happens to the flow rate?
It decreases.
Explain the graph
The pressure along the pipe decreases with friction because mechanical energy is lost as heat, and if mechanical energy decreases, so does pressure
A decrease in radius (stenosis) does what to the hydraulic resistance?
It increases the hydraulic resistance
What happens to the ΔP if hydraulic resistance increase?
It increases too, so does the flow rate
Q = (( π r4 ) / (8 μ L) ) represents
conductance (vascular)
Effect of more than one vessel in series to the vascular resistance
ΔP T = (r1 x r2 x rn ) Q
Increase of resistance is directly proportional to the number of vessels
Effect of more than one vessel in parallel to the vascular resistance
Vascular resistance = resistance of each vessel / number of vessels
Resistance is inversely proportional to the number of vessels.
Vascular resistance is _____ proportional to conductance
inversely
Friction is more relevant in arterioles than in capillaries because___
There are more capillaries than arterioles.
Analogy to the generation 5-15 in bronchioles
Turbulent flow causes
increase in velocity due to decrease area
Reynolds number
Re (kinetic energy / friction stress)
Low Re numbers =
High Re numbers =
Low = laminar regime (<1000) High = turbulent regime (> 1500)(jet > 2000)
Neutonian fluids have a ____
viscosity
