pressure and flow in arteries and veins

Question 1

how is arterial pressure measured

Answer 1

auscultation of Korotkoff sounds using sphygmomanometer and stethoscope

Question 2

what are the sounds heard when measuring arterial pressure

Answer 2

silence
tapping - systolic pressure 
thumping - longer pumping sounds 
muffled - continuous sound, rarely heard
silence - diastolic pressure

Question 3

pros and cons of measuring arterial pressure

Answer 3

cons:
accuracy - underestimates pressure by 5-10mmHg discontinuous - can only take a measurement every few mins
needs care - hard to hear sounds if there is background noise

pros:
non-invasive
cheap

Question 4

what is the role of elastic arteries

Answer 4

act as pressure reservoir
dampen down pressure variations
energy is absorbed by the elastic walls

Question 5

what affects the pressure wave

Answer 5

stroke volume
velocity of ejection
elasticity of arteries
TPR

Question 6

what is normal arterial pressure

Answer 6

120/80mmHg
arterial pressure (especially pulse pressure) increases with age
arteries become less elastic with age –> hypertension

Question 7

what affects the rising phase of blood pressire

Answer 7

stroke volume
velocity of ejection - less time to absorb elastic pressure

strength of contraction affects peak systolic pressure
both rising and falling affected by elasticity
TPR affects mainly falling phase and diastolic pressure

Question 8

pressure and flow from arteries to veins

Answer 8

pressure falls throughout the vascular tree
small drop through the arteries from ~95 to 90mmHg (low resistance conduit)
large drop through arterioles from ~90 to 40mmHg (resistance vessels)
pressure is already low when blood gets to capillaries (needs to be as they are thin walled)
leaves a small pressure difference pushing blood back through the veins from ~20 to 5mmHg (the systemic filling pressure)

Question 9

pulmonary circulation pressure

Answer 9

~1/5th of systemic but follows the same pattern

Question 10

what is velocity of blood related to

Answer 10

total cross section

fastest in aorta and vena cava, slowest in capillaries

Question 11

pressure and flow in veins

Answer 11

low pressure - pressure difference driving blood back to the heart is low
vessels are distensible and collapsible - external influences affect flow (they can expand and accomodate lots of blood, blood can also be squashed out of them)

Question 12

external influences on flow in veins

Answer 12

gravity
substracts ~40mmHg from head and adds ~80mmHg in the feet
change in pressure doesnt have an effect on arteries as pressure gradient stays the same

Question 13

what affect does gravity have on the legs

Answer 13

venous distension
thin walled and can’t withstand the pressure - blood pools in the venules and veins in feet and legs
reduced EDV, reduced preload, reduced SV, reduced CO, reduced MAP
orthostatic postural hypotension

Question 14

what effect does gravity have on veins in the neck

Answer 14

causes venous collapse in the neck

can be used to estimate CVP

Question 15

how is jugular collapse used to estimate CVP

Answer 15

height of jugular collapse can be used to estimate CVP
higher pressure inside the central vein = higher height of collapse
(normally isnt visible as it is below the clavicle)
high jugular vein indicates high CVP

Question 16

skeletal muscle pump significance

Answer 16

significance re:
rhythmic vs static exercise - only occurs during rhythmic exercise due to repeated contraction and relaxation of the muscle, sustained muscular contraction is bad for the heart
standing still in the heat - lots of peripheral vasodilation, blood pools in veins in legs and feet, faint
DVT - compression socks mimic skeletal muscle pump to push the blood back
varicose veins

Question 17

what is the skeletal muscle pump

Answer 17

venules and veins passing through the skeletal muscle back to the heart
when they contract the vessels inside are squashed and blood is pushed back up to the heart

Question 18

what is the respiratory pump

Answer 18

inhalation reduces pressure in the thorax and increases pressure in the abdomen, these pressures are transmitted through to the blood vessels in these areas
increased venous return during inhalation - breathe faster and deeper, increased EDV

Question 19

what is venomotor tone

Answer 19

state of contraction of the smooth muscle surrounding the venules and veins
mobilises capacitance

• activate symp NS, contraction of smooth muscle around vessels, blood expelled back to the heart, increased EDV

Question 20

what is systemic filling pressure

Answer 20

pressure created by ventricles and transmitted through the vascular tree to the veins

Question 21

what is the main thing pushing blood from venules and veins back to the heart

Answer 21

systemic filling pressure

Question 22

what is involved in clotting

Answer 22

formation of a platelet plug and a fibrin clot

Question 23

what is fibrinogen

Answer 23

inactive precursor protein that is already present, converted into fibrin by thrombin

Question 24

what are the 6 anti-clotting mechanisms of the endothelium

Answer 24

stop blood contacting collagen 
production of prostacyclin and NO
production of TFPI
expression of thrombomodulin
expression of heparin 
secretion of t-PA

Question 25

how does stopping the blood contacting the collagen inhibit clotting

Answer 25

no platelet aggregation

physical barrier between blood and BM

Question 26

how does prostacyclin and NO inhibit clotting

Answer 26

both inhibit platelet aggregation

Question 27

how does TFPI inhibit clotting

Answer 27

tissue factor pathway inhibitor
stops thrombin production
fibrinogen isn’t converted into fibrin

Question 28

how does thrombomodulin inhibit clotting

Answer 28

binds thrombin and inactivates it

Question 29

how does heparin inhibit clotting

Answer 29

inactivates thrombin

Question 30

how does t-PA inhibit clotting

Answer 30

tissue plasminogen activator

plasminogen –> plasmin which then digests the clot