cardiovascular mechanics 3

Question 1

describe the design of the circulation

Answer 1

in pul circulation blood is oxygenated and loses CO2
in systemic circulation it is pumped to the body
L and r ventricles - separate but coupled pumps ie same organ
the heart as a pump creates a pressure gradient, blood flow from high - low pressure
flow to capillaries for a short diffusion distance

Question 2

structure of artery

Answer 2

3 layers of muscle: adventitia, media, intima

Question 3

capillary structure

Answer 3

small, thin wall, largest SA

Question 4

venuole and vein structure

Answer 4

less muscular, valve for unidirectional flow

Question 5

pressue through bv

Answer 5

drop in arterioles

small decline in capillaries

Question 6

proportion of systemic blood in vessel

Answer 6

related to pressure in bv
and compliance
more in veins - capitance vessel - can decrease blood storage I n times of stress

Question 7

why dos blood flow

Answer 7

follows the pressure difference - diffuses against the length of resistance tube
resistance can be altered to change blood perfusion

Question 8

what is darcy’s law

Answer 8

pressure difference can change resistance
Q = flow of blood (volumetric flow)
R = resistance through capillaries

pressure difference = Q*R

Question 9

haemodynamic determinants of blood pressure

Answer 9

MAP = CO - R

MAP stays constant, blood flow modulated by R

Question 10

assumptions for relationship for CO, MAP and R

Answer 10

steady flow of blood
rigid vessels
R atrial pressure negligible

Question 11

describe the pressure in the circulation

Answer 11

drops in arterioles
pressure difference allow flow through capillaries
pressure is built up again in pulmonary circulation

Question 12

describe the resistance to blood flow

Answer 12

depends on viscosity, length of tube, radius
viscosity and length constant
R = 1/R(power of 4)
half radius - decrease flow 16x

Question 13

when does viscosity change

Answer 13

pathophysiology

climb mountain

Question 14

describe distribution of blood flow to organ

Answer 14

at rest CO = 5L/min 
exercise CO= 15L/min 
change flow by innervating vascular beds 
increase heart rate 
decrease storage in veins 
blood to skeletal muscle

Question 15

what is lamina flow

Answer 15

blood flow in linear motion
velocity constant at any 1 point and flows in layers
fastest near centre of lumen
slow near walls - resistance when blood cells hit the wall (adhesive forces with the wall)

Question 16

turbulent flow

Answer 16

flow erratically
form eddys
prone to pooling
pathophysiological changes to endothelial lining of BV

Question 17

describe blood flow and shear stress

Answer 17

adhesive forces between fluid and surface
draw parabolic velocity profile - draw tangent, gradient of vel profile is the shear rate
shear rate * viscosity is the shear stress

Question 18

describe lamina shear stress

Answer 18

high sheer stress
promote endothelial survival and quiescence
cells aligned in direction of flow
secretion promote vasodilation and anticoagulation (secretions are important in the coagulation cascade)

Question 19

describe disturbed shear stress

Answer 19

low shear stress
promote endothelial proliferation, apoptosis and shape change
secretions promote vasoconstriction, coagulation and platelet aggregation - not good, clotting occludes bv
change in shear stress to disturbed is age related in branch near carotid arteries

Question 20

how is bp measured

Answer 20

cuff occlude arterial pressure at 130mmHg
won’t hear anything
decrease to 120mmHg - hear terbulant because partially occluded - taps every heart beat
decrease occlusion more - vessel completely open
diastolic pressure - lamina flow - disappearance of sound

Question 21

calculation for MAP (mean arterial pressure)

Answer 21

MAP = DBP +1/3PP(pulse pressure)

Question 22

why is there a difference in aortic and ventricular pressure

Answer 22

aortic valve close - aortic pressure fall slowly, ventricular pressure fall rapidly
explained by elasticity of aorta - and large arteries which buffer the change in pulse pressure
elasticity of a vessel related to compliance

Question 23

describe the wind kessel effect

Answer 23

water out of tube is pulsatile - add balloon (representative of elastic aorta) flow is less pulsatile
push still pulsatile - flow sustained because expanded aorta - maintain diastolic pressure

Question 24

describe arterial compliance and pulse pressure

Answer 24

blood enter aorta faster than leaves them - 40% SV stored by elastic arteries
recoil of arteries pressure fall slow - diastolic flow
if compliance decreases eg become stiffer with age the windkessel effect is reduced - pulse pressure increases

Question 25

describe the effect of pressure on vessel walls

Answer 25

transmural pressure causes tension that can be described by law of Laplace
T=P*R
Transmural pressure increases because blood flows through vessel cause persistent high circumferential stress = vessel distention
circumferential stress=tension/wall thickness

Question 26

describe aneurysms

Answer 26

vessel walls weaken - balloon like distension
pathological law of Laplace
aneurysm increase radius - for same internal pressure - inward force must also increase
if fibres weak - force needed cannot be produced - aneurysm expand until ruptured
same process for formation of diverticuli in gut - pocket form so gut can contract less
cure for aneurysm - surgery - put mesh around to maintain vessel continuity
ecophysiological and cardiological ways to detect them

Question 27

what is compliance and what does it depend on

Answer 27

the relationship between transmural pressure and vessel volume
depend on elasticity

Question 28

compare venous and arterial compliance

Answer 28

venous 10-20x higher at low pressure

store more blood

Question 29

how do you change volume stored in veins

Answer 29

increase smooth muscle contraction and synthetic drive, decrease radius, increase pressure
small changes distend veins - increase volume stored in them

Question 30

how does gravity affect blood flow

Answer 30

different transmural pressure in different body parts
the extend that gravity increases the increases hydrostatic pressure varies with height - approx. 100mmHg
standing increase hydrostatic pressure in legs as a result of gravity
blood transiently pool in veins - high compliance - without compensation this reduced CO and blood pressure - hypotension - faint (syncope)

Question 31

mechanisms to cope with gravity

Answer 31

stimulate skeletal muscle pump - more blood returns to heart
valves for unidrirectional flow
respiratory pump - ease blood back to the heart as quickly as possible - diaphragm, intrathoracic pressure

Question 32

what happens if you have incompetent valves

Answer 32

dilated superficial veins in the leg, pool of blood in legs - varicose veins

Question 33

what happens with prolonged elevation of venous pressure

Answer 33

oedema

even with intact compensatory mechanisms