Part 2: Cardiovascular Physics Flashcards
Blood flow is proportional to what?
Flow(V) = change in P/R
Adaptation of Ohm’s law
Total fluid energy has 3 components…
Hydrostatic pressure
Gravitational potential energy
Kinetic energy
What is the difference between resistance in parallel and resistance in series?
In series:
R = R1 + R2 + R3 etc
In parallel:
1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc
There addition of further resistance in series will increase resistance whereas addition of a resister in parallel will decrease total resistance
Resistance to flow equation
R = (8 x viscosity x length) / pie x radius power of 4
What is Poiseuille’s equation?
Flow is related to pressure gradient, viscosity, length of tube, radius
note radius to the 4th - therefore small changes in radius have large affect on flow
Describe laminar flow
Flow is most rapid in the centre of lumen and slowest on the edges with parabolic effect.
How does turbulent flow occur?
Critical velocity is reached when Reynolds number is exceeded (ie inertia forces dominant viscous forces). This usually occurs around 40cm/sec in blood
What affects viscosity of blood?
- haematocrit, plasma proteins
- flow - blood is not newtonian and viscosity decreases at slower velocity
Decreased viscosity makes turbulent flow more or less likely?
More likely, in anaemia turbulence is more likely
What is the law of laplace?
Blood vessel transmural pressure = (wall tension x thickness) / radius
Essentially a larger vessel will have greater outward distending force than smaller vessels. A dilated heart therefore must work harder to overcome large tension
What affect does passive stretching have on vessels and flow?
Vessels passively stretch somewhat in response to increase pressure, this causes disproportionate increase in flow as increase radius increases flow.
