Exam 7 - Biophysics / Vessels Flashcards
1
Q
Basic principles of circulatory function
A
- Rate of blood flow to each tissue is controlled based on need
~ local control by arterioles
~ CNS and hormones can control in emergencies
~ if metabolic need increases…blood flow increases - CO is controlled by sum of all local tissue flows
~ Venous return determines CO automatically (starlings curve)
~ CNS can help in emergencies - Art. pressure regulation is independent of local blood flow and CO
~ this allows to change flow in localized regions
~ controlled by sensor feedback systems and kidneys
~ If pressure falls: Increase contractility
Constrict large veins (move volume to arteries)
Constrict arterioles (hold more volume in arteries)
Kidneys hold onto more volume…increase CO
(First 3 happen quickly…kidneys take time)
2
Q
Ohm’s law
A
- dP = Q x R
- Flow is same for vessels in series
- Pressure drop determined by change in resistance
- Smaller the vessel…higher the velocity
- Smaller the vessel….higher the pressure drop
3
Q
Reynold’s number
A
- tendency for turbulence to occur
- velocity in vessel is faster in center….no flow at boundary
- Shear Stress: force on wall by moving blood…wants to pull wall w/ it
~goes up with viscosity / flow
~goes down increase in radius by factor of 3 - turbulent flow increases resistance and damage to cells
- AS or AI can create turbulent flow (each have unique murmur)
- Re = (velocity x diameter x density) / (viscosity)
- Turbulence in straight tube at 2000….side branches at 200-400
- decrease due to radius and venturi effect - will get turbulence in aorta….very seldom in smaller arteries
4
Q
Poiseuille’s Law
A
- Shows factors that affect resistance to flow in system
- diameter has greatest effect on flow (factor of 4)
- arterioles can cause BIG changes in flow with SMALL changes in d
5
Q
Vessels in parallel
A
- Flow in = Flow out
- Flow doesn’t have to be same through each vessel
- Total R across network is smaller than R for any one vessel
6
Q
Bruits
A
- vibration you can feel caused by flow
7
Q
Murmur
A
- sound caused by flow
8
Q
What can change viscosity of blood
A
- Temperature (inverse)
- [ Plasma protein ] (direct)
- [ RBC ] (direct)
- Shear stress (direct)
- Blood flow (inverse)
- Blood is 3x more viscous than water
- Can be a problem in capillaries… capillary sludging…especially cold
9
Q
Viscosity on bypass
A
- dilute plasma proteins (V goes down)
- Dilute RBC (V goes down)
- Cool patient (V goes up)
- Give vasoconstrictor (V goes up potentially) (careful at cool temps)
10
Q
Systemic circulation
A
- Peripheral circulation
- maintains constant internal environment in 3rd space
- sophisticated irrigation system
~ gets nutrients and removes wastes when needed
11
Q
Pulmonary circulation
A
- Brings blood flow in contact w/ resp mem of lungs
12
Q
Arteries
A
- transport blood at high pressure
- elastic / strong walls
- not muscular
13
Q
Arterioles
A
- controlled by ANS
- meta arterioles and pre cap sphincters really control local flow
- control flow through capillary bed
- strong / muscular walls….can contract all the way closed
- can dilate with 7x increase in radius
14
Q
Capillaries
A
- all exchange here
- very thin with gaps between cells (cap pores)
~ pores very permeable to water / Na / K / Cl / glucose - O2 / CO2 / ethanol move directly across cells
- proteins stay inside
15
Q
Endothelial cells
A
- line entire CV system including heart and valves
- control transcapillary solute and water exchange
- active tissue: alive / interact / respond
~ aid/inhibit coagulation
~ affect function of platelets and neutrophils
~ major role in perfusion injury
~ interact w/ plasma proteins and activate them
16
Q
Transcapillary fluid movement
A
- Filtarion = out of capillary / more at arterial end
- absorption = in / more at venous end
- overall net filtration
- Hydrostatic Cap pressure (push out) = 20-25
- Hydrostatic interstitial pressure (push in) = -3
- Osmotic Cap pressure (pull in) = 28
- Osmotic interstitial pressure (pull out) = 8
17
Q
Lymphatic system
A
- path for excess i fluid and proteins to return to circ system
- flushes bacteria and other foreigners out of i fluid into nodes
- same size / more porous than capillaries / less numerous
- one way valves
- return to blood near right side of heart
- 2.5 L returned each day
18
Q
Venules
A
- collect blood from capillaries
- direct blood to veins
- capacitance vessel (store blood)
19
Q
Veins
A
- transport blood at low pressure
- thin walls / valves
- velocity greater than caps but lower than arteries
- shift blood to arteries when needed (capacitance vessel)
- Peripheral veins: veins outside thorax
- Central veins: major veins in thorax
~ affected by thoracic pressure
~ lowest pressure in vascular system
~ determine ventricular filling
20
Q
Aorta specs
A
ID = 2.5 cm Thick = 2 mm # = 1 X-sectional = 4.5 cm^2
21
Q
Arterioles specs
A
ID = 30 um Thick = 20 um # = 50,000,000 or 5x10^7 X-sectional = 400 cm^2
22
Q
Capillaries specs
A
ID = 5 um Thick = 1 um # = 10^10 X-sectional = 4500 cm^2
23
Q
Vena CAva specs
A
ID = 3 cm Thick = 1.5 mm # = 2 X-sectional = 18 cm^2
24
Q
Blood volume distribution
A
Arteries - 13%
Arterioles/Caps - 7%
Veins/venules/sinus - 64%
- Systemic Circ = 84%
- Heart = 7%
- Pulmonary Circ = 9%
25
Circ system facts
- Flow highest in Arteries/arterioles (500 mm/s)
- Flow lowest in Caps (0.5 mm/s)
- Most blood volume in veins and venules (64%)
- Pressure highest in Arts/arterioles (mean 100) (pulsatile flow)
- Pressure lowest in Caps (25) (stop pulsatile flow)
- Highest resistance in arterioles
- Pulmonary pressure much lower than systemic pressure
26
Mean Arterial Pressure
- constant even if pulse pressure widens
- not changed by over/under dampening
MAP = (COxTPR) + CVP
- any change in CO or SVR will change MAP
Or MAP = PD + (1/3 x Pulse pressure)
- MAP is closer to PD than PS i normal conditions
- If HR goes up....MAP closer to PS
- MAP goes up with age: Decrease in distensibility
Increase in SVR
Changes in control mechanisms
27
Relationship of CO / Pre-load / Venous return
- Increase in VR increases the rest
- Changing diameter of artery/vein does not change SVR/Flow
~ they are elastic / dispensable / compliant
- Vein elasticity helps move blood in/out of arteries (VR)
- Artery elasticity helps with ejection of blood into aorta
~ Arterioles are what change flow/SVR
28
Distensibility
= (dV) / (dP x original V)
- % change in vol. per 1 mmHg change in pressure
- Veins 8x more distensible than arteries (so thin)
~same increase in pressure would lead to 8x increase in volume
- Pulmonary arteries 6x more distensible than systemic arteries
- Pulmonary and systemic veins are the same (8x more than syst art)
29
Compliance
= dV / dP
- Distensibility x initial volume
- systemic veins 24x more compliant than systemic arteries
~ 8x more distensible / hold 3x the volume
- Volume-pressure curves show compliance
30
Volume-Pressure Curves
- Inverse of line slope is Compliance
- High compliance is good / Low is bad
- Arterial: Normal compliance = 2 ml/mmHg
Normal 700 ml = 100 mmHg mean pressure
Drop to 400 ml = 0 mmHg
Small change in volume = big change in pressure
- Arteries help heart generate pressure
- Venous: Normal compliance = 100 ml/mmHg
Normal volumes = 2000-3500 mls
Normal pressure = 0-20 mmHg
Large change in volume = small change in pressure
- Sympathetic tone shifts curves up and left - bigger slopes
- decreased compliance
- shifts volume from one compartment to another
- increases venous return
- Decrease sympathetic tone - dilates...pressure drops
- increased compliance
- holds volume in compartment
31
Stress-Relaxation of vessels
- Response to volume changes
- No ANS innervation.....all innate to vessels
- Vessels will dilate/constrict to keep BP normal
- sometimes can't 100% compensate
- increase vol cause relax....decrease vol cause constrict
- hemorrhage is example (will cause constriction)
32
Arterial pulse
- Distensibility allows aorta to accept ejected blood w/o huge increase in pressure
- Energy put into stretching aorta is given back in diastole to push blood through vascular tree....w/o stretch...pressure would be 0 once ejection ends
- Pressure pulse is faster than flow pulse due to inertia in aorta
- flow must overcome inertia of blood already in aorta
- Compliance goes down as you move down tree (rate goes up)
- higher compliance = lower transmission rate
- In aorta...pressure wave is 15x faster than actual flow of blood
33
Normal SV
60-100 mls
34
Pulse Pressre
= Ps - Pd
= SV / arterial compliance (if all SV stay in aorta during ejection)
- widens as you move down tree... lower comp
- Stronger contractions will increase pulse pressure
- Pp increases with age due to big drop in arterial compliance
35
Interpretation of blood pressure
- systolic and diastolic pressure alone not good estimators
- systolic and diastolic are affected by more than just SVR
- HR / SV / PP
- Better to look at MAP and arterial pulse pressure
36
Right atrial pressure (CVP)
- normally 0 (range: -5 to +30)
- Balance of ability of R heart to pump AND blood return to RA
- Decreased by: increase contractility (more blood pumped out)
Decrease venous return
- low volume/low venous tone/constrict arterioles
- Increased by: decrease contractility / high VR
- Normally heart can compensate for VR and CVP change is minimal
37
Venous resistance
- Periph venous pressure usually 4-6 mmHg higher than CVP
- due to collapse of veins entering thorax
- CVP must rise this amount before you see increase in peripheral venous pressure
- Intra-abdominal pressure can rise to 15-30 if:
- pregnant / tumors / obesity / ascites (fluid build up)
38
Effect of gravity on venous pressure
- When standing, CVP is close to 0 because heart pumps out excess blood
- Everything below heart is higher
- Pressure in feet 90 mmHg IF standing still
- movement helps keep this lower (usually around 20 if standing)
- can lose 10-20% of CBV in 15-30 min if standing still
- Neck is 0 because atmospheric pressure collapses veins
- Theoretical 10 mmHg lower in brain due to gravity
- One way valves help fight gravity too
39
Blood reservoirs
- some organs can hold onto blood and put into CBV if needed
- Spleen: 100 mls
- Liver: several hundred mls
- Abdominal veins: 300 mls
- Venous plexus: several hundred mls
- Heart: 50-100 mls (drops in sympathetic stimulation)
- Lungs: 100-200 mls
