Haemodynamics Flashcards
what is haemodynamics?
physical factors that control blood flow
what does blood consist of ?
Blood is a fluid.
Consists of cells and plasma (fluid that contains proteins and electrolytes)
what is the difference between plasma and serum?
serum is plasma without clotting factors
Name some diseases that can affect whole blood viscosity
polycythaemia
thromobocythaemia
leukaemia
what is C-reactive protein a clinical indicator of?
inflammation
what is flow?
vol transferred per unit time (ml/min)
what is pressure?
force per unit area (mmHg)
what is vascular resistance?
resistance to flow in blood vessels
features of laminar flow
adjacent layers of fluid slide over each other
‘streamline’
silent
flow is fastest in central layers
features of turbulent flow
disorganised
noisy
when is there turbulent flow
when the pressure increases but the flow can’t match it.
critical Reynolds number exceeded
e.g changing direction of vessels(branching), in stenosed arteries, stenotic heart valves
factors affecting resistance to flow
diameter
length
viscosity
diameter is most important as length doesn’t change and viscosity is regulated
where is resistance highest and lowest?
low in aorta as is has a large diameter and is short
high in smallest arteries and arterioles
what is velocity
distance blood moves in given time (cm /s)
why is velocity at capillary level slow
capillary brings oxygenated blood to tissues so enables exchange
what is pulse pressure
systolic bp - diastolic bp
what is pulse
shock wave that arrives slightly before blood itself
what can cause a strong pulse ( increasing pulse pressure)
heart block-bradycardia
vasodilation-decrease in peripheral resistance -hot bath, pregnancy
elite athletes - systolic increased and diastolic decreases
theory behind measuring arterial bp
normally blood flow is laminar so silent
if pressure in cuff is inflated above systolic pressure there is no blood flow (no sound)
as the cuff is deflated below systolic pressure blood will begin to flow but artery is partially compressed so flow is turbulent and you will hear kortokoff sounds.
cuff deflates more and when it passes below diastolic pressure there is no sound as now there is laminar flow
what happens to flow in a stenosed vessel
velocity increases through the stenosis and turbulence occurs beyond it.
a thrill is felt
bruit is heard
what happens if cuff is too small/big
small-overestimate bp
big-underestimate bp
how does the effect of gravity maintain pressure gradient
pressure above heart is greater and below heart if lower.
when GPE is considered it increases the pressure at the feet so there is a slight gradient allowing blood flow.
what is postural hypotension and what causes it
dizziness upon standing
low stroke vol as there is pooling at feet creating hypotension
what is normal bp
s- less than 120
d- less than 80
mean arterial pressure equation
mean arterial pressure =DBP + (SBP-DBP)/3
CARDIAC OUTPUT EQUATION
CARDIAC OUTPUT=HR X SV
mean arterial pressure equation
cardiac output x total peripheral resistance
