Pressure and Flow in Arteries and Veins Flashcards
How can arterial pressure be measured?
Ausculatation of Kortokoff sounds using sphygmomanometer and stethoscope
What is the order of sounds that should be heard when measuring arterial pressure?
- Silence
- Tapping
- Thumping
- Muffled
- Silence
What sound is an indication of systolic pressure?
Start of the tapping sound
What sound is an indication of diastolic pressure?
Disappearance of sound
What are the disadvantages of using a stethoscope and sphygmomanometer to measure arterial pressure?
- Tends to underestimate
- Can’t get a second by second reading which means a continuous reading cannot be obtained
- Takes practice
What are the advantages of using a stethoscope and sphygmomanometer to measure arterial pressure?
- Non-invasive
- Cheap
What vessels act as pressure reservoirs?
Elastic arteries
What do elastic arteries do?
Damps down pressure variations
What can elastic energy stored during filling of vessels be used for?
To push blood into smaller vessels
What is the pressure wave affected by?
- Stroke volume
- Velocity of ejection
- Elasticity of arteries
- Total peripheral resistance
What is ‘normal’ arterial pressure?
120/80 mmHg
How does age affect arterial pressure?
Increases
Where is the systemic filling pressure found?
In the venules and veins
How does pressure vary across the components of the CV system?
Decreases from
- Left ventricle
- Arteries
- Arterioles
- Capillaries
- Venules/veins
- Right atrium
What happens to pressure throughout the vascular tree?
It falls
What is velocity related to?
Total cross section
How does velocity differ across components of the CV system?
- Fastest in the aorta and vena cava
- Slowest in the capillaries
What is the pressure drop in through the arteries?
- Small drop
- 95 to 90 mmHg
- Low resistance conduit
What is the pressure drop in through the arterioles?
- Large drop
- 90 to 40 mmHg
- Resistance vessels
Why is it good that the pressure is already low in the capillaries?
They are thin walled
What is the pressure difference pushing blood back through the veins?
- Small change
- 20 to 5 mmHg
- Systemic filling pressure
How does the pulmonary circulation pressure compare to that of the systemic circulation?
1/5th of the systemic
What does the low pressure in veins mean?
The change in pressure driving blood back to the heart is low
What does the fact that vessels are distensible and collapsible mean?
External influences affect flow
What external influences affect flow?
- Gravity
- Skeletal muscle pumping
- Respiratory pump
- Venomotor tone
- Systemic filling pressure
What does gravity not affect?
Driving pressure from arteries to veins
What are the effects of venous distension in the legs caused by gravity?
- Decreased EDV
- Decreased preload
- Decreased SV
- Decreased CO
- Decreased MAP
- Can cause orthostatic hypotension
What can venous collapse in the neck caused by gravity be used to estimate?
Central venous pressure
What happens to pressures during inhalation?
Negative pressure created in the lungs and a positive pressure in the abdomen
What is the skeletal muscle pump significant in?
- Rhythmic vs static exercise
- Hot guardsmen
- Deep vein thrombosis
- Varicose veins
What is venometer tone?
State of contraction of the smooth muscle surrounding the venules and veins
What does the venometer tone do?
Mobilises capacitance
What is the systemic filling pressure?
Pressure created by ventricles and transmitted through vascular tree to the veins
