Pressure and Flow in Veins Flashcards
How do you measure Korotkoff sounds?
Sphygmomanometer and stethoscope
What are the disadvantages and advantages of using a sphygmomanometer?
Discontinuous, accuracy, needs care and skill
Non-invasive and cheap
What causes Korotkoff sounds?
Turbulent blood flow
Silence above systolic and under diastolic
What sounds are heard on stethoscope?
Silence, tapping, thumping, muffled and then silence again
How does an oscillatory blood pressure measurement calculate arterial pressure?
Vibrations from turbulent blood flow are measured
Peak of vibrations at MAP
Transducer measures this
Explain ventricular contraction on aorta and arteries?
Ventricle contracts, Semilunar valve open and blood ejected from ventricle to arteries and then aorta expands so can store pressure in elastic walls
Explain ventricular relaxation on aorta and arteries?
Isovolumic ventricular relaxation, semilunar valves shut so prevents backflow of blood and then elastic recoil sends blood forward into circulatory system
How does elastic arteries act as pressure reservoir?
Damps down pressure vibrations
What is pressure wave affected by?
Stroke volume, Velocity of ejection, Elasticity of arteries and TPR
Describe pressure and flow from arteries to veins?
Pressure falls throughout vascular tree and velocity is related to total cross-sectional area
What causes small drop in pressure through arteries?
Low resistance conduit
around 95 to 90 mmHg
What causes larger drop in pressure through arterioles?
Resistance vessels
Around 90 - 40mmHg
Describe the pressure in capillaries?
Low which is good as thin walled
Describe pressure in veins?
Small pressure difference pushing blood back through veins as systemic filling pressure
From 20 - 5 mmHg
What is pulmonary circulation pressure?
1/5 th of systemic circulation pressure as need to be low
Describe velocity and cross-sectional area
Fastest in aorta and vena cava as small total cross-sectional area
Slowest in capillaries as have high cross-sectional area
How does external influences affect flow?
Vessels are distensible and collapsible
Does gravity affect driving pressure from arterioles to veins?
No
What effect does gravity have on flow and pressure in veins?
Venous distension in legs
Decreases EDV, preload, SV, CO and MAP
Can get orthostatic hypotension which causes venous collapse in neck
What causes orthostatic hypotension?
Veins and venules are thin walled so increase in pressure causes them to distend (expand) so blood pulls here and less blood gets to heart
Explain negative pressure on pressure and flow in veins?
Negative pressure means pressure inside vessel is lower than outside so causes vessels to become squished and collapse
What happens if venous pressure increases?
The point of collapse will move further up and can be visible
Can rise due to stress
Can look for point of collapse in internal jugular vein
Very prominent and full of blood
What can raised JVP cause?
Can show right sided heart failure
How does the skeletal muscle pump affect the pressure and flow in veins?
Rhythmic contraction increases venous return and EDV
If muscle contracts it can squeeze on veins and venules so blood squeezed in both directions
How does compression socks help?
Compress vessels in legs so blood can get back to heart quicker
Describe the respiratory pump on pressure and flow in veins?
Increased respiratory rate and depth increases venous return and EDV
How does inspiration lead to larger pressure gradient and increased venous return?
Diaphragm moves down and caused negative pressure in thorax and positive below
Causes larger pressure difference so blood is pushed back to heart and therefore causes increased venous return
How does venomotor tone affect pressure and flow in veins?
Is a state of contraction of smooth muscle surrounding the venules and veins
Mobilises capacitance and increases EDV
What is the systemic filling pressure?
Pressure created by ventricles and transmitted through vascular tree to veins
What does clotting involve?
Formation of platelet plug and fibrin clot
Platelets are exposed to collagen and also send chemical signals to other platelets
How is fibrin made?
Fibrinogen is converted to insoluble fibrin by thrombin
What are some endothelium mechanisms for to stop platelet aggregation?
Stops blood contacting collagen
Produces prostacyclin and NO which inhibits platelet aggregation
What endothelium mechanism stops thrombin production?
Produces tissue factor pathway inhibitor (TFPI)
What endothelium mechanism inactivates thrombin?
Expresses thrombomodulin
Expresses heparin
What endothelium mechanism causes plasmin production?
Secretes tissue plasminogen activator so plasminogen can convert to plasmin and digest clot
