Pressure and Flow in Arteries and Veins Flashcards
When the ventricles contract, what change occurs in the left ventricular internal pressure?
Rises from 0 to 120mmHg (in a normal individual)
As the systolic pressure rises, what happens to the aortic valve?
Aortic valve opens and blood is expelled into the aorta
What is the period of ventricular contraction known as?
Systole
What is the systolic pressure?
The maximal pressure during systole
What does systolic pressure drive?
Drives blood through the aorta, causing it to distend
What occurs when the aortic valve closes?
Left ventricle relaxes so that it can be refilled with blood from the left atrium via the mitral valve
What is the period of ventricular relaxation known as?
Diastole
What happens to blood flow and pressure during diastole?
Blood flow and pressure diminish but do not fall to 0 as the elastic recoil of the aorta continues to exert a diastolic pressure on the blood
What is the minimum level of diastolic pressure in a normal individual?
About 80mmHg
What is the pulse pressure?
The difference between systolic and diastolic pressure
What is the mean arterial blood pressure (MABP)?
The pressure averaged over the entire cardiac cycle
What percentage of the cardiac cycle is spent in diastole?
Approximately 60%
What is the MABP approximately equal to?
Diastolic pressure + 1/3rd of the pulse pressure
What are Korotkoff sounds used for?
To measure the arterial pressure via auscultation of the brachial artery using a sphygmomanometer and a stethoscope
When are there no Korotkoff sounds?
In a normal artery with smooth flow and no turbulence, and in a completely occluded artery with no blood flow
Why does blood flow become turbulent when measuring blood pressure?
The cuff applies pressure to the underlying brachial artery, as the cuff is gradually deflated and pressure decreases flow becomes turbulent until the pressure is completely removed and normal smooth flow resumes
What is the typical progression of Korotkoff sounds when measuring blood pressure?
Silence - smooth flow, artery completely occluded
Tapping
Thumping
Muffled
Silence - pressure completely removed and normal smooth flow resumed
What does the first tapping sound heart represent?
Systolic pressure
What does the point at which the muffled sound stops and artery is silent again represent?
Diastolic pressure
What are the advantages and disadvantages of measuring blood pressure using a cuff, sphygmomanometer and stethoscope?
Advantages
- cheap
- non-invasive
Disadvantages
- accuracy
- discontinuity
What arteries act as a pressure reservoir? How do they achieve this?
Elastic arteries, act to dampen down pressure variations
What is the pressure wave affected by?
Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance
What is the normal arterial pressure?
120/80mmHg
Do changes in pressure mainly affect systolic or diastolic pressure?
Diastolic
Does pressure fall or rise as it moves through the vascular tree?
Falls
Is the blood in the atrium low or high pressure?
Low pressure
What is the drop in blood pressure as blood flows through the arteries?
Drops from around 95 to 90mmHg
What is the drop in blood pressure as blood flows through the arterioles? Why is this?
Drops from around 90 to 40mmHg as these are resistance vessels
Why is low pressure necessary in the blood at the capillaries?
Necessary to allow exchange to occur
Also as capillaries are only one cell thick so could not withstand high pressures
There is a small pressure difference pushing the blood back through the veins, what is this known as?
Systemic filling pressure
What fraction of the systemic filling pressure does the pulmonary circulation pressure account for?
1/5th
What is velocity of blood related to?
Total cross section of the vessels
Why can external influences affect flow, venous pressure and venous return in veins?
As vessels are distensible and collapsible
What external factors can affect venous flow, pressure and return?
Gravity Skeletal muscle pump Respiratory pump Venomotor tone Systemic filling pressure
What effect does gravity have on the veins?
Does not affect the driving pressure from the arteries to the veins but does cause venous distension in the legs
What effect does gravity have on EDV, preload, SV, CO and MAP?
Decreases these
What kind of hypotension can gravity cause?
Orthostatic (postural) hypotension
What can gravity cause in the neck?
Venous collapse
What can the height of the jugular venous pulse be used to estimate?
Central venous pressure
What does a bulging jugular vein in the neck indicate?
The point of collapse and a high central venous pressure
The skeletal muscle pump is significant in relation to what?
Rhythmic vs static exercise
Deep vein thrombosis
Varicose veins
During what kind of exercise does the skeletal muscle pump work?
Rhythmic exercise
What does sustained static exercise result in?
Increase in peripheral vasodilation
What effect will breathing deeper and faster have on the draw of blood back to the heart?
Breathing deeper or faster will draw more blood back to the heart
What is the venomotor tone?
The state of contraction of the smooth muscle surrounding the veins and venules
What does venomotor tone mobilise?
Capacitance
What is the systemic filling pressure?
The pressure created by the ventricles
What is the systemic filling pressure transmitted through?
Through the vascular tree to the veins
