Pressure & Flow in Arteries and Veins Flashcards
What is systolic pressure?
The pressure of the blood during the heart contraction (systole).
When left ventricle contracts and pushes blood into the aorta.
What is diastolic pressure?
The pressure of the blood when the heart is at rest between heart beats (diastole).
What is the difference between systolic and diastolic blood pressure?
The pulse pressure
How can blood pressure be calculated
Flow x Resistance
What factors increase systolic pressure
Increased cardiac output
Reduced blood vessel compliance
Increased pulse pressure - increases w atherosclerosis
What are korotkoff sounds?
Sounds that medical personnel listen for when they are taking blood pressure using a non-invasive procedure
What is the effect of high diastolic pressure on the aorta?
There is a higher total peripheral resistance so the aorta finds it harder to release blood
What is the effect of elastic vessels on pressure variations?
Dampens them down
What happens to the aorta during ventricular contraction?
- Ventricle contracts
- Semilunar valves open. Blood pours from ventricles flow into the arteries.
- Aorta and arteries expand and store pressure in elastic arteries
STRETCH
What happens to the aorta during ventricular relaxation?
- Ventricular relaxation
- Semilunar valve shuts, preventing flow back into ventricle
- Elastic recoil of arteries sends blood forward into rest of circulatory system
RECOIL
What is pressure wave effected by?
Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance
What is the dicrotic notch?
Low point after closure of the aortic valves and precedes the secondary dicrotic wave.
The notch is frequently used as a marker for the end of the ventricular ejection period.
What feature of arteries allows maintainance of high pressure during high systolic pressure?
Elastic fibres
How does pressure change from arteries - arterioles - capillaries - venules?
Aka through the vascular tree
Decreases
Drops in vascular tree with numbers
Small drop through arteries (95 to 90mmHg)
Large drop through arterioles (90 to 40mmHg)
Pressure is low when reach capillaries which is good bc they are thin walled
Leaves a small pressure difference pushing blood back through veins (from 20 to 5mmHg)
What is name given to the blood pressure left to bring the blood back to the heart?
Systemic filling pressure
What is the pulmonary circulation pressure?
1/5th of systemic
What is velocity related to?
Cross sectional area
Fastest in aorta and vena cava, slowest in capillaries
Vessels of veins are distensible and collapsable what does this mean?
External influences affect flow
Does gravity affect driving pressure from arteries to veins?
NO
What is the effect of gravity in venous blood in the leg?
Causes venous distension - Decreased end diastolic volume, decreased preload, decreased stroke volume, decreased cardiac output and decreased mean arterial blood pressure (orthostatic hypotension)
What is the effect of gravity in the neck?
Causes venous collapse in the neck - can be used to estimate central venous pressure
Where in the body has -20 mmHg?
Head and neck
Where in the body is +100 mmHg?
Feet
If pressure in the arteries always remains constant what does this mean for the driving force of the blood?
Always remains the same
What can impact pressure and flow in veins?
Gravity
Skeletal muscle pump
Resp pump
Ventricular tone
Systemic filling phase
What are veins in legs surrounded by and what is their impact?
Skeletal muscle
When that muscle contracts, as you can see here, it shortens, as you know, but it also becomes fatter.
Squeezes on veins and venules, push blood in both directions.
So blood is going to be pushed up back towards the heart, but it’s also going to be pushed down towards the feet.
What is the significance of skeletal muscle in veins in legs?
The significance of this is that during exercise, skeletal muscle will contract and squeeze spare capacitance back to the heart, increase venous return and increase end diastolic volume.
That’s important because at high heart rates you have that decreased filling time and decreased end diastolic volume.
Can also casue DVT due to ncreased venous pooling in the veins and venules in their leg and static blood is more likely to clot
What is the impact of the respiratory pump?
Increase resp rate and depth increase venous return and EDV
Expiration - small pressure gradient
Inspiration - larger pressure gradient, increased venous return
What is venomotor tone?
State of contarction of smooth muscle surrounding veins
What is the impact of venomotor tone?
Mobilises capacitance and increases EVD
What is systemic filling pressure?
Pressure created by ventricles and transmitted through vascular tree to the veins
How can systemic pressure change in exercise
Systemic filling pressure can change. For example, during exercise, it can increase.
During exercise you have increased sympathetic tone and that can increase contractility.That will cause the mean arterial pressure to increase.
How can total peripheral resistance change during exercise?
Decreased total peripheral resistance.
Arterioles are more dilated, it’s therefore easier to push blood from the arteries into the arterioles
So here you would get a smaller decrease in the pressure as the blood moves
By the time blood gets down to the veins and venules, there’s going to be higher pressure here and you’re going to have a bigger driving force pushing blood from the veins and venules back to the right atrium.
What does clotting involve?
Fomration of platelet plug and fibrin clot
What is the basement membrane made from?
Collagen
What happens when blood vessels are damaged?
Platelets have access to the collagen in that basement membrane of blood vessel.
Platelets become activated and they’ll stick to it, platelet plug forms.
Platelet plug is weak so needs fibrin clot to make it more solid.
What is fibrin?
Large insoluble protein and it forms mesh over the top of the platelet plug.
How is fibrin formed?
Fibrin is formed from its precursor fibrinogen, and the enzyme that converts fibrinogen into fibrin is called thrombin.
What prevents inappropiate clotting?
Endothelium has developed a number of different anti-clotting mechanisms.
How does the endothelium prevent inappropriate clotting?
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 and inactivates it
* Expresses heparin
Inactivates thrombin
* Secretes tissue plasminogen activator (t-PA) *
* Plasminogen → plasmin and digests clot
