Arterial system and haemodynamics
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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