pressure and flow in arteries and veins Flashcards
what are the positives and the negative of arterial lines?
Arterial lines are continuous and accurate but are invasive, so for patients in AE and ICU
how do we listen to Korotkoff sounds?
sounds using a sphygmomanometer and stethoscope
how are the Korotkoff sounds described in theory?
point at which taps are first heard is systolic BP, point at which they disappear is diastolic
what are the advantages and disadvantages of using a blood pressure cuff?
discontinuous, accuracy (size of cuff affects accuracy), needs care and skill
non-invasive, cheap, quick and easy to use once you get the hang of it (so useful for hypertensive patients)
Manual monitoring is subjective as each clinician may hear the Korotkoff sounds differently at different times
how do automatic BP machines measure BP?
they pick up oscillations (vibrations) from the turbulent blood flow. highest peak on the graph is mean arterial pressure and it predicts diastolic and systolic
what happens to the aorta during systole?
when ventricles contract during systole, blood flows into the aorta and it acts as a pressure reservoir
when ventricles relax during diastole, elastic recoil of aorta pushes out the remaining blood and shuts the aortic valve, so blood is still pumped during relaxation (explains notch/blip on the pressure wave)
what factors affect the pressure wave?
Stroke volume
Velocity of ejection (most crucial)
Elasticity of arteries
Total peripheral resistance (Graph will be more gradual at the falling phase if constricted arterioles as more time and energy needs taken to get it through, vice versa for dilation)
describe the cross-sectional area and the velocity in the aorta compared to capillaries?
aorta - area lowest but velocity highest
capillaries - area greatest but the velocity is lowest (look over the spaghetti analogy in the silverthorn book)
think of ‘still waters run deep’, rivers narrower and more velocity but lochs wider but less velocity
what are the important qualities of veins which make them good for their job?
pressure is low and thin walls means vessels are distensible and collapsible
what does clotting involve?
formation of a platelet plug and then a formation of a fibrin clot (can think of platelets being bricks and fibrin the mortar)
fibrinogen is turned into fibrin by the enzyme thrombin
what are the anti clotting mechanisms?
Stops blood contacting collagen - no platelet aggregation
produces prostacyclin and NO - both inhibit platelet aggregation
produces tissue factor pathway inhibitor (TFPI) -stops thrombin production
expresses thrombomodulin - binds thrombin and inactivates it
expresses heparin - also inactivates thrombin
secretes tissue plasminogen activator (t-PA) - plasminogen - plasmin and digests clot
