Fluid Dynamics Flashcards
What drives blood flow along a blood vessel?
Hydrostatic pressure gradients (pressure exerted by fluids - blood)
What is the pressure of the aorta and vena cava?
The force generated by ventricular ejection raises aortic BP to around 100mmHg
The pressure in the vena cava is about atmospheric around 0mmHg
What drives blood flow?
Difference in the pressure of the flow of blood
Why is arterial pressure pulsatile?
Due to the intermittent blood ejection pressure which varies between successive ejection
What is the typical peak systolic and diastolic pressure?
120mmHg systolic
80mmHg diastolic
What is typical pulmonary pressure?
25/10mmHg
What is resistance of a vessel?
The measure of friction that impedes flow (How difficult is it for blood to flow between two points at any given pressure)
What is Darcy’s Law?
change in P = dqR
P - Change in P is pressure difference between two points
Q - Flow is the rate of transfer of volume of fluid
R - resistance to flow
What are the 3 main factors which determines resistance?
1) Viscosity of fluid
2) Vessel Length
3) Vessel diameter
What equation describes fluid dynamics?
Poiseulle’s equation
R = (128/pi )((nL)/d^4)
R is inversely proportional to nL/d^4
R = resistance to flow n = fluid viscosity L = length of tube d = diameter of tube
What is the biggest factor affecting the resistance?
Lumen size
Diameter to the power of 4 in Poiseuille’s equation
What are the reasons why poisuelle’s equation doesn’t hold for resistance blood vessels all the time?
Entrance flow continues 1m down aorta
Blood isn’t water and viscosity changes due to cellular components
Heart rate is pulsed so not smooth poiseuille flow
Acccording to the poiseuille equation, which vessels should have the greatest resistance? Why do they not?
Cappillaries
- They are extremely short and run in parallel (effectively increasing diameter)
Hence, the greatest resistance is in the next smallest vessels: arterioles . This affects total peripheral resistance
