Week 1 - Pressure and Flow in Arteries and Veins Flashcards
How do we measure arterial pressure? (3 ways)
arterial line, sphygmomanometer and oscillatory blood pressure machines (both upper arm korotkoff)
What does an arterial line measure and how good is it?
continuously measures arterial pressure with catheter in radial or brachial artery. invasive but accurate.
What does a sphygmomanometer measure? benefits and negatives?
use stethascope and listen to when you hear sounds and when they stop. non-invasive and cheap but discontinuous and needs accuracy and skill
What does an oscillatory blood pressure machine measure?
vibrations generated from turbulent blood flow. measures vibrations when vessel is open until its so open that flow is laminar. non-invasive and cheap but discontinuous and needs accuracy and skill
What is the issue with cuffs?
need to be right size. if you use a too large one, you’ll underestimate blood pressure.
What affects pressure in arteries? (4)
- stroke volume - higher is more pressure
- velocity of ejection - higher is more pressure
- elasticity of arteries - more = less pressure. ageing reduces elasticity, increases systolic pressure and decreasing diastolic pressure
- total peripheral resistance - more resistance in arterioles means lower diastolic pressure
Why does blood pressure rise as we age?
less elastic tissue. causes high systolic and lower diastolic.
How does blood pressure change from aorta to veins?
- 120mmHG in aorta
- 90mmHg in arteries. low resistance means easy for blood to flow through to pressure change isn’t large
- 40mmHg in arterioles - resistance.
- 20mmHg to in veins and venules to 5mmHg when reaches atrium
How does blood pressure change in the pulmonary circulation? what’s the pressure?
graph will look the same, but values will be much lower as less pressure is needed to move blood through. 25/10mmHg
How does velocity change throughout the vessels?
highest in aorta as lowest cross sectional area (only 1 aorta) - lowest in capillaries as highest cross sectional area. decreases in arteries and arterioles. increases in veins and vena cava as there are less and they have a lower cross sectional area
What affects the velocity of blood flow?
cross sectional area of vessels. low = high velocity and vice versa
What 5 factors affect pressure and flow in the veins?
gravity, skeletal muscle pump, respiratory pump, venomotor tone, systemic filling pressure
How does gravity effect venous pressure and flow?
when you stand, pressure becomes more positive in your legs and more negative in your head. these cancel eachother out
What can standing up too quickly cause?
blood can pool in legs., reducing venous return, reducing EDV and preload, reducing stroke volume, thus reducing cardiac output. this can lead to lack of blood in brain and thus lightheadedness
How is raised JVP caused by pressure changes in veins?
negative pressure in head veins. pressure outside may cause them to collapse, leading to increased JVP to try and get all the blood back to the heart. also caused by heart failure
How does skeletal muscle pump impact flow/pressure in veins?
veins and venules are surrounded by skeletal muscle. when this contracts, vessels are constricted and blood is pushed back up and also towards heart. valves prevent backflow. but when running, walking, cycling, this increases pressure of blood back to heart, increasing EDV and preload. counteracts effects of high heart rate decreasing preload.
How does the respiratory pump effect venous flow and pressure?
on inspiration, diaphragm moves down, causing negative pressure in thorax and positive pressure below, which is transmitted to vessels, increasing pressure and EDV.
How does venomotor tone effect venous flow and pressure?
tone is activity of smooth muscles. sympathetic NS releases noradrenaline, binding to b2 receptors on smooth muscle of vessels, causing contraction and more blood back to heart.
How does systemic filling pressure effect venous flow and pressure?
this is the main factor - other 4 factors are on top of this. this is pressure created by ventricles which pushes blood out and all the way around back through veins to the heart
How does heart failure cause raised JVP?
heart is not efficiently pumping the amount of blood it has, so jugular vein is evident and has high pressure to try and push blood through, and due to pooling.
What is the mean arterial pressure?
average pressure in the arteries throughout the cardiac cycle
