Pressure and flow in arteries and veins Flashcards
How do you measure arterial pressure?
Auscultation of korotkoff sounds using sphygmomanometer
& stethoscope
What is the series of the sounds you should hear as you increase the pressure in the cuff ?
Silence, tapping, thumping, muffled and silence
What is the advantage of sphygmomanometer
& stethoscope
beign used to measure arterial pressure?
Non-invasive and cheap
What is the disadvantage of sphygmomanometer
& stethoscope
being used to measure arterial pressure?
accuracy,
discontinuous
needs care
What do elastic arteries do in the terms of pressure variation?
Elastic arteries act as pressure reservoir
- damps down pressure variations
What is the pressure wave affected by?
- stroke volume
- velocity of ejection
- elasticity of arteries
- total peripheral resistance
What is the average normal arterial pressure?
120/80mmHg
When does the pressure decrease on the pressure wave graph?
When blood goes through arterioles as they are resistance vessels
What is pulse pressure?
Distance between systolic and diastolic pressure
Is there a big or small drop in pressure through arteries?
Small drop through arteries (from ~ 95 to 90 mmHg)
low resistance conduit
Is there a big or small drop in pressure through arterioles?
Large drop through arterioles (from ~ 90 to 40 mmHg)
the resistance vessels
What pushes the blood back through the veins in capillaries?
Leaves a small pressure difference pushing blood back through the veins (from ~ 20 to 5 mmHg)
the systemic filling pressure
What fraction is the pulmonary circulation pressure of the systemic
1/5th
How is velocity related to total cross section
Lower the total cross section, the higher the velocity
fastest in aorta and vena cava, slowest in capillaries
What are examples of external influences and factors that affect vaso pressure and return?
Gravity Skeletal msucle pump Respiratory pump Venomotor tone Systemic filling pressure
How does gravity affect arteries and veins?
Does not affect driving pressure from arteries to veins
Does causes venous distension in legs
Decreases EDV, preload, SV, CO and then MAP
causes orthostatic hypotention
Results in venous collapse in neck and can be used to estimate central venous pressure
What can the venous collapse in the neck estimate?
Central venous pressure
What is the effect of skeletal muscle pump on the pressure and flow in veins?
rhythmic vs static exercise
hot guardsmen
deep vein thrombosis
varicose veins
What is the effect of venomotor tone on pressure and veins?
= state of contraction of the smooth muscle
surrounding the venules and veins
- mobilises capacitance
What is the systemic filling pressure?
pressure created by ventricles and
transmitted through vascular tree to the veins
What does clotting involve?
Formation of platelet plug
Formation of fibrin clot by fibronogen into fibrin by thrombin
What are the anticlotting mechanisms of the endothelium?
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 & inactivates it
Expresses heparin
-also inactivates thrombin
Secretes tissue plasminogen activator (t-PA)
-plasminogen = plasmin & digests clot
