Pressure and Flow in Arteries and Veins Flashcards
How is arterial pressure measured
Auscultation of Korotkoff sounds using sphygmomanometer and stethoscope
Systolic pressure sound
Tapping
Diastolic pressure sound
Silence
Order of pressure sounds from high cuff pressure to lower
Silence, tapping, thumping, muffled, silence
Disadvantages of measuring by Korotkoff sounds
Low accuracy
Discontinuous
Needs care
Advantages of measuring by Korotkoff sounds
Non-invasive
Cheap
Energy changes in aorta during systole and diastole
Absorb energy during systole and release energy during diastole
Elastic arteries act as
Pressure reservoir
Pressure wave of arteries is affected by
Stroke volume and velocity of ejection - rising phase
Elasticity of arteries - both
Total peripheral resistance - falling phase
Normal arterial pressure
120/80mmHg
Effect of age on arterial pressure
Increases
Pressure from arteries to veins
Decreases
Pressure drop in arteries
Small = 95 to 90 mmHg
Pressure drop in arterioles
Large = 90 to 40 mmHg
Pressure drop in veins
Small = 20 to 5 mmHg
Velocity is related to
Total cross section
Velocity is greatest in
Aorta and vena cava
Velocity is lowest in
Capillaries
Veins are
Distensible and collapsible
External influences that affect flow in veins
Gravity Skeletal muscle pump Respiratory pump Venomotor tone Systemic filling pressure (main)
Pressure in body due to gravity
Low pressure at head and high pressure at feet
Gravity does not affect
Pressure from arteries to veins
Gravity causes
Venous distension in legs and neck
Effects of venous distension in legs
Decrease EDV, preload, stroke volume, cardiac output and main arterial pressure
Orthostatic (postural) hypotension
Venous collapse in neck can be used to
Estimate central venous pressure
What causes jugular vein to collapse
Pressure outside vein being greater than pressure inside vein
Skeletal muscle pump
Contracts around vein squashing the blood inside upwards towards heart as blood can’t flow backwards - increases venous return
Things of significance to skeletal muscle pump
Rhythmic (good) vs static (bad) exercise
Heat
Deep vein thrombosis
Varicose veins (swollen)
Respiratory pump
With each inhalation pressure in the thorax decreases which increases the pressure gradient resulting in more venous return
Venomotor tone
State of contraction of the smooth muscle surrounding the venules and veins - mobilises capacitance
Systemic filling pressure
Pressure created by ventricle and transmitted through vascular tree to the veins (usually 5mmHg)
Clotting involves
Formation of platelet plug and fibrin clot
How is fibrin made
Made from fibrinogen by the action of thrombin
Blood flow is so slow in capillaries that it is in danger of
Clotting
Effect of stopping blood from contacting collagen
No platelet aggregation
Prostacyclin and NO
Inhibit platelet aggregation
Tissue factor pathway inhibitor (TFPI)
Stops thrombin production
Thrombomodulin
Binds to thrombin and inactivates it
Heparin
Inactivates thrombin
Plasminogen activator
Digests clot
What exhibits anti-clotting mechanisms
Endothelium
