Lec 10 Hemodynamics Flashcards
4 Hemodynamic principles
- pressure
- flow
- resistance
- capicitance
What primarily determines resistance of blood vessel?
radius
What does connecting blood vessels in series do to overall system resistance?
increase resistance
What does connecting blood vessels in parallel do to overall system resistance?
decrease resistance
What does Q stand for?
flow
what does C stand for?
vessel compliance
Does blood flow up or down pressure gradients? What does this mean for vascular pressure [in aorta vs arterioles vs capillaries vs venules vs veins]
- blood flows down pressure gradients
- pressure must decrease through circulation
- aorta»_space; arteries»_space; arterioles»_space; capillaries»_space; venules»_space; veins»_space; vena cava
What are 4 examples in body of flow down gradients?
- ions cross cell membrane to create action potential
- blood moving through circulatory system
- plasma crossing capillary wall
- solutes reabsorbed in kidney
What is ohm’s law?
Q = (P[final] - P [initial]) / R = delta P /R
Q = flow P = hydrostatic pressure R = resistance
What is relationship between velocity and vessel area?
- velocity is proportional to flow, inversely to area
Q = vA
Q = flow A = cross sectional area v = blood velocity
What is definition of flow vs velocity?
- flow = how many RBCs pass a particular point
- velocity = how fast does a single RBC move
What is poiseuille’s equation?
Determines blood vessel resistance
R = 8ηl/πr^4
R = vessel resistance l = vessel length η = blood viscosity r = vessel radius
What is significance of poiseuille’s equation – what type of vessels have biggest resistance?
longer vessels, smaller radius, more blood viscosity
Do shorter or longer vessels have more resistance?
longer vessels
does more or less blood viscosity cause more resistance?
more blood viscosity
Does large or smaller vessel radius cause more resistance?
smaller vessel radius
Does blood viscosity increase or decrease with hematocrit?
increases
What is viscosity?
How easy for fluid to move
if large force required to move fluid = high viscosity
What is compliance [definition, equation]
C = V/P –> compliance = volume/ pressure
low compliance = stiff, difficult to fill with fluid
high compliance = loose, easy to fill with fluid
How can you find compliance in a graph of pressure vs Volume % increase?
slope!
higher slope = higher V/P so higher C
Is compliance of veins or arteries higher?
veins have high compliance
arteries have low compliance
Do veins or arteries hold most of the blood? Why?
Veins because they have high compliance which means they are loose and easy to fill with fluid
How does flow change between vessels in series?
flow must be identical
How to calculate flow of vessels in parallel?
- total flow is divided into parallel vessels
Q tot = Q1 + Q2 + Q3
Are pressure drop and flow same or different between parallel vessels
- pressure drop through parallel vessels is the same
- flow through parallel vessels can be different [total flow is sum of parallel flows]
How to calculate resistance in series?
- overall resistance is sum of individuals
R tot = R1 + R2 + R3
if R2»_space; R2 and R3 then R tot = R2
How to calculate resistance in parallel?
Overall resistance is less than each individual
1/Rtot = 1/R1 + 1/R2 + 1/R3
Do capillaries have high or low resistance – individually? as a system?
Capillaries each have high resistance
BUT body has 3 billion capillaries in parallel, so v. low overall resistance
Which section of vasculature has greatest resistance? How can you calculate?
arterioles
Q = deltaP/R so –> R = delta P /Q
THUS: since same Q [flow] same for all parts of vasculature [in series], arterioles have highest delta P so highest R
Is blood flow through capillaries slow or fast [v]? Why?
Very slow flow in each capillary Vcap = Q total/A total Qtot = overall CO Atot = overall cross sectional area since Atot is very big --> v must be small
What is radius of capillary?
3.5 x 10 e -6 m [micro m]
What is flow through single capillary?
CO / 3x10^9 [since theres 3 billion capillaries in parallel]
How does body control flow to different regions?
- if resistance increased in one region/organ system –> divert flow from this region and increase flow to other organs
What is the TPR?
total peripheral resistance
What is significance of smooth muscle in arterioles?
- means resistance can be regulated [in capillary one cell thick so can’t do anything to make individual capillary greater or smaller]
