Arterial system and haemodynamics Flashcards
Where is arterial blood pressure determined?
In the elastic arteries
Where will you find pulsatile pressure?
In the aorta and large arteries
What does the aorta do to pulsatile pressure? And why?
Dampens pulsatile pressure
Ensure continuous flow into the circulation
Ensures blood pressure is maintained during diastole
How do you calculate pulse pressure?
Systolic pressure - diastolic pressure
How do you calculate mean arterial blood pressure?
(SP-DP)/3 + DP
What happens to the elastic wall during systole?
It distends
Energy is stored
What happens to the elastic wall during diastole?
It recoils
Blood propelled forwards
What limits how fast blood can move through arteries?
Systemic vascular resistance
Where is pressure lowest?
In the veins
What 3 factors determine resistance to blood flow in a single vessel?
Vessel length
Blood viscosity
Radius
What determines the viscosity of blood?
The hematocrit
What is the hematocrit?
The ratio of red blood cells to volume of blood
What could alter the hematocrit?
Anaemia
Altitude
Dehydration
Pregnancy
Describe laminar flow
Flow in straight line
Normal pattern of flow
Highly efficient
Follows Poiseuille’s Law
Where does blood flow fastest?
In the middle
Describe turbulent flow
Occurs where flow velocity is high
Inefficient
Cannot apply Poiseuille’s law
What might cause turbulent flow?
Large artery branches Pregnancy Exercise Valve defects Arterial stenosis
How does arterial stenosis lead to turbulent flow?
Arterial stenosis reduces area of valve
Blood is ejected at a higher velocity
What two things determine arterial blood pressure?
Blood volume in the arterial system (cardiac output)
Resistance to blood flow (total peripheral resistance
How do you calculate arterial blood pressure?
Cardiac output x total peripheral resistance
What determines systolic pressure?
Stroke volume
Aortic/arterial distensibility
Ejection velocity
Diastolic pressure of previous beat
What determines diastolic pressure?
Arteriolar resistance
Very high heart rate
What affect does ageing have on blood pressure?
Older persons vessels have lost elasticity
Loss of elastin
No distension so pressure increases during systole
No recoil during diastole so diastolic pressure decreases
Widened pulse pressure
What affect does vasodilation have on flow?
Increases flow
What affect does vasoconstriction have on flow?
Decreases flow
What is normal tone of blood vessels?
Slightly constricted
What controls vasoconstriction and vasodilation?
Endothelial factors
Local mechanisms
Central neural mechanisms
Hormonal mechanisms
What does constriction of arterioles to one organ result in?
Decreases flow to that organ only
What does constriction of arterioles to multiple organs result in?
An increase in total peripheral resistance
Therefore an increase arterial blood pressure
When might constriction of arterioles to multiple organs be necessary?
Standing
Haemorrhage
Give examples of local factors that control flow
Metabolic mechanisms
Myogenic mechanisms
Autoregulation (both the above)
What nervous system is responsible for vasomotor tone?
Sympathetic nervous system
What does an increase in sympathetic nervous activity result in?
Vasoconstriction
