Pressure and flow in arteries and veins*** Flashcards
How is arterial pressure physically measured
auscultation using stethoscope which is applied to the brachial artery (biggest brachial artery) distal to the cuff of a sphygmomanometer (blood pressure cuff) that change in pressure measuring and listening for the systolic and diastolic blood pressure which represents the arterial pressure
Why can no sound be originally heard in auscultation
As there is no blood flow due to high pressure
when pressure is gradually reduced what kind of sound can be heard, and why is this
A tapping sound, caused by the turbulence of blood now able to pus past due to reduced pressure
What does the tapping heard represent
systolic pressure
What is the next sound heard on the auscultation
A Thumping sound after tapping
What is the sound heard in the next stage which represent diastolic pressure
A Muffled sound
What is arterial pressure measured with
Auscultation of Korotkoff sounds using sphygmomanometer
& stethoscope
What is the disadvantages of measuring arterial pressure
Variation of around 10mmHg -quite alot
Can get a continuous read of pressure changing
can cut out the background sound in auscultation
What is the advantage of measuring arterial pressure
Non invasive
cheap
What is normal systolic and diastolic pressure
120mmHg
80mmHg
What do the elastic arteries act as
pressure reservoirs
What does the filling stage caused by systolic depend on
the elasticity of the arteriole wall
What affects the pressure wave of the filling stage into the arterioles from there arteries
- stroke volume
- velocity of ejection
- elasticity of arteries
- total peripheral resistance
What causes a change in normal arterial pressure
ageing as arteries become less elastic
What is a benefit of the pressure fall when blood flows from arterioles to venules
prevents blood being expelled backwards
Where does the pressure always remain high in the blood vessels
in the elastic arteries
What is the pressure change from elastic to muscular arteries
small pressure drop of 95-90mmHg
Why is there a massive pressure change in the blood from the arteries to the arterioles (e.g. roughly 90mmHg-40mmHg)
As the arterioles are resistance vessels
What happens to pressure passing down vascular tree
a continual decrease
The small pressure difference pushing blood back through the veins is called what
a systemic filling pressure
What is the drop in pressure for the systemic filling pressure
20-5mmHg
How much of pulmonary circulation pressure makes up systemic circulation pressure
1/5th
What happens to the velocity as the total cross section of BV increases
The velocity proportionally decreases
Where is velocity the quickest
the aorta,
Vena cava
What has the biggest cross section therefore the slowest velocity
the capillaries
Why does the velocity increase for BV of smaller cross section
as must increase in speed to maintain the same flow rate of those BV with bigger cross section
(which means more blood is moving at a pace, so smaller must increase space to make up for lack of volume moving)
What does the low pressure in the veins allow
the pressure difference to drive blood back to the heart
What is the two characteristics of veins that allow external influences to affect the flow
Veins are distensible & collapsible
What is external forces that affects veins flow rate
Gravity skeletal muscle pump respiratory pump venomotor tone systemic filling pressure
What condition can the effects of gravity cause
orthostatic postural hypotension
venous distension - swelling of legs
venous collapse
What affect does gravity have on the pressures of your body as you stand up
Pressure in the legs increases (20+80=100mmHg) as the pressure in your head decreases 20-40= -20mmHg)
How does orthostatic postural hypotension lead to you fainting
The increased pressure swelling in legs results in a decreased venous return which decreases EDV, therefore reducing the preload, then the stroke volume, and further cardiac output and mean arterial pressure , the decreased pressure to the brain and lack of oxygen due to decreased cardiac output propels you to faint
How does gravity cause venous collapse (jugular vein)
Due to the decrease mean arterial pressure, pressure becomes sub atmospheric, therefore pressure outside is higher than inside so results in a collapse
How can CVP be measured from jugular vein
as the jugular vein will become visible if CVP increase above sub atmospheric e.g. 20mmHg is high
What does a bulging jugular vein indicate
raised blood pressure e.g. angry
What is the importance of the skeletal muscle pump
each time skelteal msucle contract its squeezes the vein directing the blood back to the heart and increasing venous return
What affect does static exercise have on the ability of the skeletal muscle pump and cardiac out put
Means there is a long contraction of muscle, so there is cut off of blood flow due to compression on the vein, meaning less venous return by skeletal pump and less preload so decreased cardiac output
What is the affect of rhymic exercise on the skeletal pump and the cardaic output
The contractions are periodic, so in only compressed for short periods of time therefore skeletal pump maintains venous return and preload
What is the venmotor tone
state of contraction of smooth muscle surrounding veules and veins
What does a venmotor tone enable
mobile capacitance - giving veins the ability contract and push blood back to the heart (increasing EDV)
What happens to the systemic filling pressure during exercise
It increases
What is the affect of deep vein thrombosis on the pressure and flow in the veins
Deep vein thrombosis causes a pooling of blood in the veins - blood clot - which prevents the flow of blood and causes an increase pressure in the legs
What causes deep vein thrombosis
Immobility
What is the affect of varicose veins on blood flow and pressure on the veins
Stops blood flowing properly due to the formation of enlarged (dilated) sections of veins - this can result in an increase in pressure
What does the respiratory pump aid the flow of blood in the veins
The harder and the more frequent you breath, increases the venous return to the heart maintaining preload
