Fluid Dynamics Flashcards
What does the slope indicate on a graph where stress is on the y-axis and strain is on the x-axis?
What is this equation?
What are the two types of stress that strain can exert?
- Stress = y axis
- strain = x axis
- slope = E = stiffness = change in pressure/ change in volume = reciprocal of compliance
- strain can exert elastic or viscoelastic stress
What type of material exerts a linear stress-strain curve? What does this indicate about energy expenditure?
elastic tissue
energy put in and energy put out are equal
What does changing slopes on a stress-strain curve indicate?
changing stiffness
changing elastance
What is a viscouselastic material?
the material has both viscous and elastic properties
some of the energy that got put into the system was stored within the system
What is stiffness dependent on?
initial strain
What concept explains the volume-pressure relationship of a chamber, vessel, tube, and is the measure of how easily a structure can be stretched?
What is the equation?
compliance
change in volume/change in pressure = compliance = reciprocal of stiffness
what does the slope of a graph with volume on the y and pressure on the x tell us?
What changes as the curve is shifted up?
it is a curve of compliance
an upward shift = material is more stretchable = more compliant = less stiff
What is potential energy stored in a column of fluid?
What is this equation?
hydrostatic pressure = (density) x (gravity) x (height)
the pressure we are measuring is the pressure agains the walls of the chamber, and the highest pressure will be at the bottom of the column
What is the equation for pressure?
force/area = pressure (N/m^2)
the impact of internal and external (surround) pressure on distensible structure
wall tension (T)
What is transmural pressure?
How can you increase transmural pressure?
what is the magnitude of this change proportional to?
the difference between internal and external pressure
Pi-Pe = T
increasing Pi (stretching a distensible tube) will increase T
the magnitude of the change in pressure is directly related to compliance
The factors influence wall tension?
What is the equation for wall tension?
Wall tension is a reflectin of the radius and the pressure of the tube in relation to what is outside
Wall tension = Law of Laplace = P * r/2h
P = transmural pressure
r = radius
h = wall thickness
so, if we make the wall thicker, the wall tension will decrease
What is Ohm’s law?
How can this be changed to match physiologic conditions?
E = IR
E= voltage ; I= current; R= resistance
change in P = QR
P= pressure; Q= flow/minute; R= resistance
What is the pressure gradient?
change in P = change in x^-1
driving force that moves biological fluids
Hydrostatic pressure from standing up affects what property when comparing pressure above and below the heart when lying down? What remains the same?
- The heart is made 0 – why we measure blood pressure at the level of the heart
- so, absolute pressure is decreased above the head, but the gradient is maintained
- below the heart, the absolute pressure has increased, but the gradient is the same
- since gradient is maintained, blood flow is not impacted
- Since pressure inside the vessels is impacted, wall tension impacted as well
- above the heart wall tension decreases
- below the heart wall tension increases
What does it mean that blood flow is laminar?
When energy is applied it deforms into layers (lamina) and moves in a streamlined pattern in layers
As you apply prressure to a volume of blood, the layber of blood closest to the wall will not move, due to friction & adhesive forces; the next layer will move a little more/faster and this continues until you get to the center
What is the impact of laminar flow on small capillaries
the red blood cells run together in the central lamina while the plasm all runs together in an outer lamina
Red blood cells also have to deform their shape to fit through the capilaries
Velocity is inversely proportional to what property of blood vessels?
What constants are true for blood flow?
velocity is proportional to cross sectional area (V=Q/A)
- closed system
- conservation of mass
- constant flow (5L/min)
What factors influence if blood is at risk for becoming turbulant?
Reynolds number of greater than what indicates turbulant flow?
- directly
- fluid velocity
- fluid density
- vessel diameter
- inversely related
- viscosity
- Reynolds number > 2000
What factor mainly determines viscosity?
hematocrit
Describe the properties of viscosity, velosity and turbulance risk on the continuum from anemia to polycythemia?
Why can obstructions, rouch surfaces or sharp turns lead to turbulance?
they can lead to increased shear, which increases the change for turbulant flow
How doe RBC deformity and temperature influence the probability of turbulant flow?
- if RBC cannot deform, this increases the viscosity and can impeded transport through cells
- low velocity = RBC aggregation = increases viscosity
- high velocity = RBC ‘elongate’ = decreased viscosity
- increased temperature decreases viscosity
What is the problem with turbulant flow?
it looks like resistance so need a higher profusion pressure to keep blood going
since blood flow is regulated, need higher blood pressure to meet physiological function
What three signs indicate turbulant flow?
- murmurs
- cardia valve lesions
- vessel stenosis
- vessel shunts
- bruit
- diseased arteries
- anemia
- thrills (intense turbulance)
What is the loss of energy as a fluid flows around a vessel? Include the equation
Resistance
R = change in P/Q
R= resistance; P= pressure; Q= blood flow
Resistance will determine which 2 factors of fluid flow?
What is the name for the inverse of resistance?
What are the 3 levels of resistance physicans talk about?
volume and distribution
1/resistance = conductance
tissue, organ and systemic
What is a starling resistor?
flow through colapsable tubes and external compression
Explain the oscilating flow that results from an initial situation of Ps>Pin>Pout
Provide an example of this type of flow
Since the surface pressure is greater than both the Pin and Pout, the tube will collapse. Howeve, since there is no flow moving through the tube, pressure will build up as fluid accumulates in the Pin. Eventually, the build-up will be greater than the Ps, and flow will occur through the tube. Once the flow is restored, the pressure Pin pressure will again decrease to less than the Ps, and the tube will again collapse and flow will cease.
This occurs during muscle contractions
Resistance is influenced by what 3 factors?
- vessel characteristic
- fluid medium
- circuit characteristics
Vessel radius will have a HUGE effect on resistance (inversely) smaller the vessel=higher resistance
Length and viscosity will have a direct effect on resistance
What factors influence vessel cross sectional area?
- vascular tone; contractile state of smooth muscle
- wall compliance
- internal pressure
What determines series vs. parallel circuit in the body?
arrangement of organs relative to pressure sourece (heart)
organs = resistors
When you add resistors to a circuit in series waht happens to the total resistace, flow, and pressure?
Where are the 2 places this happens in the body?
adding resistance in series increases total resistance
flow decreases
if you need to maintain blood flow, then pressure has to go up
Q = change in P/R
- inferior hypophysis
- liver
The cardiovascular system is a parallel circuit. What happens when you add a resistor?
When you add a resistor in parallel, total resistance decreases (resistors are added as reciprocals)
since conductance is 1/R, conductances can simply be added
The input/output pressure remains the same (pressure gradient)
this allows us to keep our blood pressure constant
To keep blood flow constant, as resistance decreases, pressure must decrease as well
Q = change in P/R
