12. Pressure and Flow in Arteries and Veins Flashcards
What sounds are measured during the measurement of arterial pressure?
auscultation of Korotkoff sounds
What 2 pieces of equipment are used to measure arterial pressure for auscultation of Korotkoff sounds?
- sphygmomanometer (around arm)
2. stethoscope
Which artery is the stethoscope placed over to hear Korotkoff sounds?
over brachial artery (in the antecubital fossa) just below the cuff
What are the 5 stages of Korotkoff sounds?
(silence)
- tapping
- soft swishing
- thumping (crisp)
- muffled (blowing)
- silence
What do the first tapping sound heard indicate?
systolic pressure
What does it indicate if tapping sounds cease?
diastolic pressure (last audible sound)
What phase is systolic pressure usually heard at?
phase 1
What phase is diastolic pressure usually heard at?
phase 4/5
What blood vessels act as pressure reservoirs? What do they do?
elastic arteries; they damp down pressure variations
What is a pressure wave affected by? (4)
- stroke volume
- velocity of ejection
- elasticity of arteries
- total peripheral resistance (TPR)
What is a “normal” arterial pressure?
120/80 mmHg
What does arterial pressure (esp. pulse pressure) increase with naturally?
increases with age
Define MAP.
- mean arterial pressure in arteries over one cardiac cycle
Define pulse pressure.
- systolic pressure-diastolic pressure
- determined by stroke volume and arterial compliance
What happens to pressure as blood travels through a vascular tree?
pressure decreases gradually
What is the pressure drop like in arteries?
- small drop in arteries (from ~95 to 90mmHg)
What is the resistance conduit like in arteries?
low resistance conduit
What is the pressure drop like in arterioles?
- large drop in arterioles (from ~90 to 40mmHg)
What is another name for arterioles?
resistance vessels (high resistance)
What is the pressure like when blood gets to capillaries?
Already low (it’s low in arterioles so lower in capillaries) which is good because they are thin-walled
What is the pressure difference/drop in veins?
- small pressure difference/drop (from ~20 to 5mmg)
Where is systemic filling pressure found?
pressure in venules and veins draining into r.atrium
What is velocity of flow directly related to?
related to total cross section of vessel (fastest velocity in aorta with small cross section and vena cava and slowest velocity in capillaries with high cross section)
Which vessels have the highest cross sectional area?
capillaries
Which vessels have the lowest cross sectional area?
aorta and vena cava
Which vessels have the highest velocity of blood flow?
aorta and vena cava
Which vessels have the lowest velocity of blood flow?
capillaries
What is the pressure which drives blood back to the heart like?
low pressure
Why do external influences affect flow of blood?
because vessels are distensible (can be dilated) and collapsible
Does gravity affect driving pressure from arteries to veins?
NO, it doesn’t affect it
What effect does gravity have on the legs?
causes venous distension in the legs which can lead to orthostatic (postural) hypotension
What is venous distension caused as a result of? (consider: EDV, preload, SV, CO, MAP)
EDV: decreases preload: decreases stroke volume: decreases cardiac output: decreases MAP: decreases venous return decreases overall
What additional effect does gravity have on the body?
causes venous collapse in the neck which can be used to estimate central venous pressure
Height of jugular collapse can be used to estimate what value?
can be used to estimate CVP (central venous pressure)
What are pros for measuring BP with a sphygmomanometer? (2)
- cheap
- non-invsive
What are cons for measuring BP with a sphygmomanometer? (2)
- discontinous
- inaccurate and takes care
How does higher ejection velocity affect the arterial pressure wave?
A higher ejection velocity means arteries have less time to react and stretch so higher peak is measured
How does the fall of TPR affect pressures?
it makes all other pressures fall ( MAP=CO xTPR)
Why does pressure in arterioles and after? (in the capillaries)
They have a high resistance which you would think would increase pressure (Pressure = flow x resistance)
However this resistance decreases flow so so each consecutive section of arteriole and the following vessels has a lower flow and therfore pressure.
What do we call the pressure difference pushing pressure difference driving blood back through veins?
Systemic filling pressure (5-20mmHg); quite small
How does skeletal muscle pump affect pressure and flow in veins? (the examples) (3)
- rhythmic and static exercise
- deep vein thrombosis
- varicose veins
How does venomotor tone affect pressure and flow in veins?
State of contraction of the smooth muscle surrounding the venules and veins; mobilises capacitance (elasticity)
What is systemic filling pressure?
pressure created by ventricles and transmitted through vascular tree to the veins (main force pushing blood to heart at rest)
What pressure can Korotkoff sounds measure?
arterial pressure
What can be estimated by jugular collapse?
central venous pressure
What is venous pressure affected by? (5)
- gravity
- skeletal muscle pump
- respiratory pump
- venomotor tone
- systemic filling pressure
Why doesn’t gravity affect the pressure driving blood from arteries to veins?
because it evenly affects veins and arteries so pressure difference is unchanged
What does venous distension cause in terms of pressure values below and above the heart?
- pressure in veins above heart can become subatmospheric
- pressure in veins below heart in the legs can become as high as 80mmHg
How does skeletal muscle pump work?
- every time a leg is moved and muscle contracted, it squashes the vein pushing blood towards the heart
- it’s an important mechanism in legs to counter venous distension
Who is at risk of having venous distension due to lack of skeletal muscle pump?
people who stand in one position for a long time (e.g. guards) as they have little leg movement to fight against venous distension
What effect do rythmic vs static exercise have on the veins?
Rythmic exercises: involves lots of contractions so lots of blood is pumped through the veins by the skeletal muscle pump.
Static exercise; e.g. weight lifting involves a sustained contraction which lets blood flow through the veins
What are guards or people who are standing for long periods of time at risk for?
deep vein thrombosis
What is the respiratory pump?
Every time you inhale you increase abdominal presure and decrease thoracic presssure.
This pushes and pulls (respectively) blood through veins from the abdomen into the heart.
The deeper the breath the more blood flow.
How does exercise affect venomotor tone?
It increases during exercise or flight/flight so the muscle contracts and pushes blood back to the heart
How do the veins themselves affect the next systemic filling pressure?
Very dilated veins pump less blood to heart
Therefore theres a smaller CO and a lower pressure produced
This means the systemic filling pressure gets lower.
What is the approximate systemic filling pressure in mmHg?
20mmHg
