Ch 9 Arterial Physiology Flashcards
What is inertia?
Tendency of body at rest to stay at rest
or
Tendency of body in motion to stay in motion
What is kinetic energy?
-Aka energy of work or motion
-Represented by velocity of blood flow
What is potential energy?
-Aka stored/resting energy
-It is the intravascular pressure, which distends vessels
-Pressure is supplied by the contraction of the heart
What is the bernoulli principle?
When fluid flows w/o change in velocity from 1 point to another, there is no frictional losses
What is ohm law?
Flow through 2 points is directly proportional to the potential difference across the 2 points, and inversely proportional to the resistance b/w them
What does capacitance mean?
-Measure of a blood vessels ability to increase the volume of blood it holds w/o a large increase in BP
-Ability of a vessel to store energy
The total energy of a system is made up of ___ + ___ energy?
Potential + kinetic
Blood will move from an area of ___ energy/pressure to an area of ___ energy/pressure?
High, lower
The highest pressure in the vascular system occurs where?
LV of heart, approx 120 mm Hg
The lowest pressure in the vascular system occurs where?
RA of heart, approx 2-6 mm Hg
What is gravitational potential energy?
-Potential for doing work, related to the force of gravity
-Ex. if blood is positioned above the RA, it has the ability to do work b/c gravity will act on the blood to move it downward
When would gravitational potential energy be reduced?
In dependent parts of the body (below RA)
What is hydrostatic pressure?
Pressure within vessels related to the reference point of the RA
When would hydrostatic pressure increase?
Increases in the lower portions of the body, the farther below the RA = the greater it is
Does gravitational potential energy + hydrostatic pressure cancel each other out?
Yes - b/c both formulas are the same but with an opposite sign
In the vascular system, energy is almost all dissipated in the form of ___ b/c of friction?
Heat
How does the bernoulli principle relate to pressure?
High pressure = low velocity
Low pressure = high velocity
(inverse of each other)
What is the most important influence on blood viscosity?
Hematocrit (concentration of RBCs)
Blood viscosity increases with an increase in ___?
Hematocrit
When would inertial loss occur?
Whenever blood is forced to change direction or velocity
(depends on the density + velocity of blood flow)
Velocity + flow are related by the following equation:
V = Q/A
(V = velocity, Q = blood flow, A = area)
Does velocity go faster or slower in a more narrow orifice?
Faster
(velocity + area are inversely related)
Which vessel has the largest cross-sectional area?
Capillaries (600x greater than the Ao, due to their large number)
(increases from Ao, arteries, arterioles, capillaries)
Which law describes flow as “steady laminar flow”?
Poiseuille’s law (although flow is actually pulsatile + does not tend to move in a laminar fashion)
What causes an increase + decrease in flow according to poiseuille’s law?
Increase:
-increase in pressure difference
-increase in radius
Decrease:
-increase in viscosity
-increase in vessel length
What factor has the greatest impact on flow?
The radius
Hemodynamic resistance is described by which law?
Ohm’s law: R = P/Q
(R = resistance, P = pressure difference, Q = flow)
The combination of poiseuille’s law + ohm’s law creates what equation?
R = 8nl/3.14r^4
(n = viscosity, l = length, r = radius)
Changes in resistance is virtually all because of variations in ___?
Radius
List the formula for resistance in series?
Rt = R1 + R2 + R3
List the formula for resistance in parallel?
1/Rt = 1/R1 + 1/R2 + 1/R3
(the more parallel = the lower the overall resistance)
Low resistance flow profiles have what type of flow?
Antegrade - feeds regions with constant high demand (ex. the brain)
(ICA, vertebral, celiac, splenic, hepatic + renal arteries)
High resistance flow profiles have what type of flow?
Antegrade + retrograde - does not feed regions with constant high demand (ex. face)
(ECA, subclavian, distal Ao, iliac, fasting superior mesenteric + resting peripheral arteries)
When would high resistance tissue beds change into low resistance beds?
-With extremity arteries after exercise
-With the SMA after eating
Turbulent flow is defined by ___ number?
Reynolds number
Re < 2000 = laminar
Re > 2000 = turbulent
What is hydraulic filtering?
It converts pulsatile output of the heart to a steady flow through the capillaries via elastic conduits + high resistance terminals
Capacitance increases or decreases with age?
Decreases b/c walls get rigid
(greater pressure during systole, reduced pressure during diastole)
Atherosclerotic changes begin with what?
A lipid streak that consists of subintimal deposits of fat
SF of fibrous + complicated plaque?
Fibrous:
-smooth surface
-composed of smooth muscle + fibrous tissue
-no calcification
Complicated:
-irregular surface
-loss of normal endothelium
-calcifications
What 2 spots does atherosclerosis typically develop in?
Branch points + bifurcations
Define what a critical hemodynamically significant stenosis is?
-A degree of narrowing at which pressure + flow are affected
-When cross sectional area is reduced by 75%
Is stenosis in a low or high resistance system more critical?
Low resistance systems (ex. carotid arteries) can become more critical with a less severe degree of narrowing compared to low flow/high resistance systems (ex. leg arteries)
What are collateral vessels?
-Pre-existing pathways that enlarge with a stenosis or occlusion
-A main mechanism to compensate for stenosis
Collateral arteries can be divided into what 3 categories?
-Stem arteries (large branches)
-Midzone collaterals (small intramuscular branches)
-Reentry arteries (vessels that rejoin a major artery, distal to the area of stenosis/occlusion)
