Pressure and flow in arteries in veins Flashcards
What is systolic pressure?
Ventricles contracting
Maximum during one heart beat
What is diastolic pressure?
Heart refilling with blood
Minimum pressure while heart at rest
What is pulse pressure?
Difference between systole and diastole
What are the Korotkoff sounds?
Turbulent flow in the blood
Explain the Korotkoff sounds
The tappy sound is systolic pressure. Some blood is able to pass though when the pressure in the artery is in systole
The thumping sound is because the artery pressure keeps rising above and dropping below the cuff pressure
Silence is diastole because the cuff no longer provides any restriction to blood flow
Why would diastolic pressure increase?
High TPR
Constricted arterioles
How do systolic and diastolic pressure vary in exercise?
Systolic pressure increases
Diastolic pressure decreases due to blood flowing to skeletal muscle
How do elastic arteries manage the pressure wave?
They act as a pressure reservoir
Damps down pressure variations
What is the pressure wave affected by?
Stroke volume
Velocity ejection
Elasticity of arteries
Total peripheral resistance
What is ‘normal’ arterial pressure?
120/80 mmHg
How does arterial pressure change with age?
Increases, especially pulse pressure
What happens to pressure throughout the vascular tree?
Pressure falls throughout
What happens to pressure as it goes through the arteries?
Small drop
From ~95 mmHg to ~90 mmHg
It’s a low resistance conduit
What happens to pressure as it goes through arterioles?
Large drop
From ~90 to 40 mmHg
They’re resistance vessels
What happens to pressure as it goes though capillaries?
It’s already low
They’re thin walled so pressure needs to be low
What is the pressure difference pushing blood back through the veins? What is the term for this?
~20 to 5 mmHg
Systemic filling pressure
What is the approx pulmonary circulation pressure in relation to systemic pressure?
~1/5 of systemic pressure
What is the velocity relationship from aorta to capillaries?
It’s related to cross-section
Fastest in aorta and vena cava
Slowest in capillaries
Why is there a velocity relationship from aorta to capillaries?
Flow remains the same throughout
TOTAL cross-sectional area increases
Means velocity has to drop
What factors affect pressure and flow in veins?
- Gravity
- Skeletal muscle pump
- Respiratory pump
- Venemotor tone
- Systemic filling pressure
Why are veins affected by external influences?
They’re distensible and collapsible
How does gravity affect venous flow?
- Distension in legs, blood pools in venules in feet due to thin, floppy walls, increases pressure in venules and veins -> lower EDV, lower preload, lower SV, lower CO, lower MAP
- Orthostatic hypertension ->if you’re super tall
- Causes venous collapse in neck -> if you can see jugular collapse then there’s been an increase in CVP
How does the skeletal muscle pump affect venous flow?
- Rhythmic vs. static exercise -> in rhythmic exercise, you get periodic contraction -> in static exercise there is sustained muscle contraction -> weightlifting can stop blood getting back to the heart
- Hot guardsman -> blood pooling as they’re not contracting their muscles
- DVT -> static blood pooling
- Varicose veins -> valves not working well, greater column of blood
How does the respiratory pump affect venous flow?
- Negative pressure in thorax
- Positive pressure in the abdomen so the harder and more frequently you breathe, the more bloods gets back to the heart
How does venemotor tone affect venous flow?
- State of contraction of the smooth muscle surrounding venules and veins
- Mobilises capacitance
How does systemic filling pressure affect venous flow?
Pressure created by ventricles and transmitted through vascular tree to the veins
