Arteries and Veins Flashcards
What are the advantages and disadvantages of measuring blood pressure?
Non-invasive and cheap.
Discontinuous, inaccurate, and requires care and skill.
What is an oscillatory BP measurement?
Turbulent blood flow creates oscillations in the blood vessel wall, which is measured by a transducer. An algorithm estimates systolic and diastolic pressures.
What occurs in the aorta and arteries in ventricular contraction and relaxation?
Contraction - aortic and pulmonary valves open, blood enters and causes expansion of the aorta and arteries.
Relaxation - aortic and pulmonary valves close, arteries recoil and send blood forward.
How do arteries change pressure?
Acts as a pressure reservoir.
Damps down pressure variations.
Increases with age.
What is the pressure wave affected by?
SV and TPR.
Velocity of ejection.
Elasticity of arteries.
How does pressure change throughout the vascular tree?
Small drop through arteries - 95 to 90.
Large drop through arterioles - 90 to 40.
Pressure is low in capillaries.
How is blood pushed back into the veins?
A small pressure difference - the systemic filling pressure (20 to 5).
How is the velocity of blood related to the total cross-sectional area?
Fastest in aorta and vena cava.
Slowest in capillaries.
Higher velocity = lower cross-sectional area.
Why do external influences affect flow in veins?
They are distensible and collapsible.
How does gravity affect venous flow?
No effect on driving pressure from arteries to veins.
Caused by orthostatic hypotension.
Causes venous distension in the legs and venous collapse in the neck.
Decreases EDV, preload, SV, CO and MAP.
How does the skeletal muscle pump affect venous flow?
Rhythmic contraction increases VR and EDV.
Significant in DVT and exercise.
How does the respiratory pump affect venous flow?
Increased RR and depth increases VR and EDV.
Inspiration creates a larger pressure gradient.
How does venomotor tone affect venous flow?
The state of contraction of the smooth muscles surrounding the venules and veins.
Mobilises capacitance and increases EDV.
How does systemic filling pressure affect venous flow?
Pressure is created by ventricles and transmitted through the vascular tree to the veins.
What are the anti-clotting mechanisms of a fibrin clot?
Prevents blood contacting collagen, production of NO - inhibits platelet aggregation.
Production of TFPI - stops thrombin production.
Expresses thrombomodulin and heparin - inactivates thrombin.
Secretes t-PA - plasminogen forms plasmin and digests clots.
