Pressure and Flow in Arteries and Veins Flashcards
What is the main method used for measurement of arterial pressure?
Auscultation of Karotkoff sounds using spygomanometer and stethoscope.
What sound is heart when cuff pressure is just less than systolic pressue?
tapping
What sound is heard when cuff pressure is between diastolic and systolic pressure?
a thumping sound
What sound is heard when cuff pressure is the same as diastolic pressure?
a muffled sound, often inaudible though
What are the advantages of auscultation of Korotkoff sounds using sphygomomanometer and stephoscope? (2)
Non-invasive
Cheap
What are disadvantages of auscultation of Korotkoff sounds using sphymomanometer and stephoscope? (3)
Accuracy
Discontinuous
Needs care
What do elastic arteries act as?
Pressure reservoirs that damp down pressure variants.
prevents pressure getting too high in systole and too low in diastole
What factors affect the pressure wave for blood in arteries? (4)
Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance
What is normal arteriolar pressure?
120/80mmHg
How does normal arteriolar pressure change with age?
It increases, as blood vessels lose elasticity.
The aorta _______ energy during systole and ________ energy during diastole.
absorbs
releases
Which factors affect the rising phase of the pressure wave?
- velocity of projection
- SV
- HR
- strength of contraction
Which factors affect the falling phase of the pressure wave?
- elasticity of arteries
- TPR
What happens at the dicrotic notch in the pressure wave?
- isovolumetric relaxation
- small and brief increase in arterial pressure due to closing of aortic valve.
In one word, what happens to pressure in blood vessels moving from the arteries all the way through to the veins?
it decreases
Between which two types of vessels is the decrease in pressure the greatest?
Explain this.
Arteries to arterioles.
Arterioles, the resistance vessels, have smaller diameters and overall larger surface area which reduces the pressure force.
Pulse pressure = ______ - ________
systolic pressure - diastolic pressure
There is a _______ _______ in pressure through arteries (from about __ to __ mmHg).
small decrease
95 to 90
There is a _____ drop through arterioles (from about __ to __ mmHg)
- the _________ vessels
large
90 to 40
resistance
How would you describe pressure in the capillaries?
Why is this good?
low, 20-40 mmHg
Because capillaries are extremely thin walled and fine.
Leaving the capillaries, a ______ pressure difference remains pushing blood back through the ______ (from around __ to __ mmHg).
This is known as the _______ ________ pressure, which returns blood to the ______ ______ of the heart.
small
veins
20 to 5
systemic filling
right side
Why is there only a small drop in pressure through arteries?
Low resistance conduit, elasticity releases energy
How does pulmonary circulation pressure compare to systemic circulation?
1/5th the size, same curve
What is the velocity of blood flow related to?
Which vessels is it fastest/slowest in?
Total cross sectional area
Fastest in aorta/arteries, slowest in capillaries.
How does velocity of blood flow relate to total cross sectional area?
Greater the total cross sectional area, the smaller the velocity.
What is the systemic filling pressure?
The pressure of blood exiting the circulatory system.
Which of the two ventricles has the lower pressure?
Why?
RV
Less pressure required to push blood through the pulmonary circulation.
Why do external influences affect flow in veins?
Due to their thin walls, they are distensible and collapse.
What effect does gravity not have on pressure and flow between arteries and veins?
It does not affect the pressure gradient, as it is acting on both arteries and veins.
Where is venous distension caused by gravity most likely to happen?
What is the clinical term for this?
What effect does this have on the heart?
Legs
Orthostatic hypotension
- decreased EDV
- decreased preload
- decreased SV
- decreased CO
- decreased MAP/afterload
The height of jugular collapse can be used to estimate ______.
Central venous pressure
If there is a high CVP, the jugular vein collapse will happen ______.
higher
Explain the concept of jugular venous collapse.
- jugular vein height increase = decrease in pressure
- pressure becomes sub-atmospheric
- venous distension
- High CVP, collapse occurs higher in neck
What are examples of external factors that affect flow in veins? (5)
Which of these is the main driving force for venous return to the heart?
- Gravity
- Skeletal muscle pump
- Respiratory pump
- Venomotor tone
- Systemic filling pressure
Systemic filling pressure
What can gravity cause in terms of flow through veins?
Venous distension in legs
Venous collapse in neck
How does the skeletal muscle pump work?
Skeletal muscle contracting in a rhythmic fashion helps pump blood back from the peripheries, as valves prevent blood moving away from the heart.
What are examples of skeletal muscle pump impacting venous flow?
Rhythmic vs static exercise
Hot guardsmen
Deep vein thrombosis
Varicose veins
How does venomotor tone affect pressure and flow in veins?
Contraction of smooth muscle round the veins helps to mobilise capacitance and increase EDV.
Describe how the respiratory pump changes the flow in veins?
- Inspiration = negative pressure in thorax/positive pressure in abdomen
What does clotting involve?
Formation of a platelet plug.
Formation of a fibrin clot.
What are the anti-clotting mechanisms of the endothelium aiming to do?
- prevent platelet plug
- prevent fibrin clot
- break down developed clots
Outline the anti-clotting mechanisms of the endothelium.
- physical barrier (no platelet aggregation)
- prostacyclin and NO production
- produces TF pathway inhibitor
- expresses thrombomodulin
- expresses heparin
- secretes tissue plasminogen activator.
What do prostacyclin and NO do?
inhibit platelet aggregation
What does TFPI do?
stops thrombin production
What does thrombomodulin do?
binds thrombin & inactivates it.
What does heparin do?
also inactivates thrombin
What does tissue plasminogen activator do?
Catalyses the reaction of plasminogen to plasmin, and plasmin digests the clot.
What is converted into fibrin and what carries this out?
fibrinogen
thrombin
