Regulation of arteriolar resistance Flashcards
What is the main way of assessing someones blood pressure/resistance?
Auscultation of Korotkoff sounds
Using Shphygmomanometer & stethoscope
This is used in General practice and in hospital settings
How does Ausculation of Korotkoff sounds work?
Cuff around the arm gets very tight, and releases pressure gradually
At different parts of the cardiac cycle, blood will be able to ‘overcome and push through’ the pressure exerted by the cuff
The sounds that are heard, indicate the pressure at which blood can overcome the pressure, thus give an indication of BP
What sounds can be heard during Korotkoff testing, and what causes each sound?
Silence:
- pressure exerted by the cuff is higher than any part of the cycle ∴ no flow ∴ no noise
Tapping:
- pressure in cuff is only overcome during strongest part of systole ∴ flow only permitted for V short period
Thumping:
- Large part of the cycle overcomes cuff’s pressure ∴ longer period of flow ∴ more thumpy than tappy
Muffled:
- Pretty much all the cycle exerts pressure > cuff so only short periods when there is no flow
Silence 2:
- Whole cycle overcomes the cuff ∴ no gaps in the noise ∴ effectively silent
What are the advantages of Korotkoff auscultation?
Non-invasive
Cheap
Quick
What are the dis-advantages of Korotkoff auscultation?
Not very accurate
Discontinuous
Needs care
How do elastic arteries contribute to smooth blood flow?
They stretch & recoil with heart contraction
This makes them act as a pressure reservoir
∴ they dampen down pressure variations
When are elastic arteries most stretched?
Ventricular systole (contraction)
Pressure is highest ∴ they expand outwards
What other feature in the CVS means elastic arteries can maintain higher blood pressure/flow during diastole?
Valves
These prevent back-flow when the elastic arteries recoil, so they squeeze the blood in the ‘forward’ direction
Although elastic arteries dampen pressure variations, the pressure curve/wave is affected by various factors
What factors affect the arterial pressure curve?
- stroke volume
- velocity of ejection
- total peripheral resistance
(+ elasticity of the arteries - as mentioned previously)
What is normal arterial pressure?
120/80 mmHg
How does arterial pressure change as you get older?
Increases with age
Systolic (pulse) pressure increases especially
Describe the shape of the pressure wave/curve
Kinda bell shaped
- Rising side is steeper than the falling side
- Small upwards blip on falling (right) side due to AORTIC VALVE CLOSING
“The maximum point on the arterial pressure wave gives ________”
Systolic pressure
“The minimum point on the arterial pressure wave gives __________”
Diastolic pressure
What is MAP?
Is it useful?
Mean arterial pressure
Useful in general indications of health, however it is useful to give systolic / diastolic instead as you can identify specific problems
At what time of the day is arterial pressure lowest?
Night (when asleep)
What can cause arterial pressure to naturally rise?
Pain
Stress
Exercise
Shaggin
Stimulant drugs
Where in the body is highest average blood pressure achieved?
Main (elastic) Arteries
Where in the body is the maximum blood pressure achieved?
Left ventricle during systole
highly variable ∴ not highest on average
Where is average blood pressure lowest?
Veins & venules
Where is the lowest blood pressure achieved?
Right atrium during diastole
How does pressure decrease through the vascular tree?
Small drop through arteries (95-90 mmHg)
Large drop through arterioles (90-40 mmHg)
- “Resistance vessels”
In capillary bed (40-20 mmHg)
In returning venules & veins (20-5 mmHg)
How is the pulmonary circulation pressure different to the systemic in terms of pressure?
Pulmonary circ is about 1/5th of the systemic’s pressure
“Blood velocity is related to _____________ and is highest in ___________ and lowest in _________”
Cross sectional area of vessel’s lumen
Highest velocity in Aorta & vena cava
Lowest velocity in Capillaries
Why does gravity affect venous flow so much?
Low pressure
Vessels are distensible, collapsable and just a bit floppy really
How does gravity affect the pressure values in veins in different parts of the body?
Subtracts about 40 mmHg in pressure from the head area:
- Lying down = 10 mmHg
- Standing = -30 mmHg
Adds about 80 mmHg to pressure at the feet:
- Lying down = 10 mmHg
- Standing up = 90 mmHg
Summarise the effect of gravity on the CVS, and describe how this is clinically useful
Does not affect driving pressure from arteries to veins
Causes venous distension in legs:
- Decreases EDV, preload, SV, CO, MAP
- orthostatic (postural) hypotension
Causes venous collapse in neck:
- Height of venous collapse can be used to estimate central venous pressure
Why is it important to flex your thigh and calf muscles if you are static and upright for long periods of time?
Low blood flow to head can cause syncope (hot guardsmen)
Risk of deep vein thrombosis
Risk of varicose vein development
Flexing skeletal muscle ‘pumps’ the blood so this is avoided
Summarise what factors affect blood flow in veins
Gravity
Skeletal muscle pump
Respiratory pump
Venomotor tone
Systemic filling pressure
Highlight the 2 main stages in clotting
Formation of platelet plug
Formation of fibrin clot
What chemical is central in converting fibrinogen to fibrin?
Thrombin
How does the epithelium prevent clot formation?
Stops blood contacting collagen
- no platelet aggregation
Produces prostacyclin and NO
- both inhibit platelet aggregation
Produces tissue factor pathway inhibitor (TFPI)
- stops thrombin production
Expresses thrombomodulin
- binds thrombin & inactivates it
Expresses heparin
- also inactivates thrombin
Secretes tissue plasminogen activator (t-PA)
- plasminogen plasmin & digests clot
What does Kortokoff tapping tell you?
Systolic pressure
What does Kortokoff silence (2) tell you?
Diastolic pressure
