Haemodynamics Flashcards
how do you define pulse pressure?
systolic pressure - Diastolic pressure
how do you define the mean pressure?
diastolic pressure + 1/3 pulse pressure
*mean pressure only applis to the peripheries not the atriums/ventricles*
how do you calculate flow (Q) ?
flow is volume movement per unit time
Q= pressure/peripheral resistance
how do we apply ohms law to circulation?
Ohms law is
V= IR
when applied to blood pressure
BP= Cardiac output x peripheral resistance
why do we hear murmers?
it is an indication of non-laminar flow/ tubulent flow causes by valve incompetence/stenosis
Why might you not hear a murmer with a mitral valve regurgitation?
left atrium is a low pressure chamber, if mitral valve incompetance is chronic you might see an enlargement of the Left atrium -
in really sick patient with a low systemic pressure, there might not be a real difference in pressure between the left atrium and the left ventricle - therefore you don’ hear a murmer?
It’s all about the difference in pressures
What is the major determinant of blood viscosity?
haematocrit - main determinant
blood with normal viscosity is xc more viscous than water
what are the other determinants of blood viscosity?
blood vessel diameter
velocity of blood flow
what is Laplaces law?
tension is related to transmural pressure and radius =
where does the majority of blood sit in our body at any particular time?
64% is in our veins
how do we calculate the velocity of blood?
V= flow/area -
it is fastest in the aorta and slowest in the capillaries
how do we increase cardiac output?
increase HR, reduce end systolic volume and increase end diastolic volume
how do we measure blood flow?
ultrasound doppler studies
how do you calculate the cardiac output knowing the stroke rate and volume?
cardiac output = L/min
stroke volume= Liters
Stroke rate = min
therfore cardiac output = Sv/Sr
