Hemodynamics

Velocity and Flow

Q (flow) = V (linear velocity) X A (x-sectional area)

Used to estimate aortic valve area and press (velocity)

A₁V₁ = A₂V₂ continuity equation

Velocity and Pressure

v = 100 cm/s 200cm/s 100cm/s

KE=1/2pv² = 3.8mmHg 15mmHg 3.8mmHg

p = density

P_total = P_lateral+ P_KE

with narrowing (stenosis): very hard for ventricle to pump against this Þ angina

Laminar vs Turbulent Flow

laminar flow:

turbulent flow:

Reynold’s number:

turbulence identification

feel or palpate neck for frill (vibration)

can hear as a murmur

Abdominal aortic anyuerysm Þ dilated artery which may produce eddy currents Þ bruit

Pressure and Flow

Hagen – Poiseuille law

blood can change its viscosity while a newtonian fluid maintains its state under variable press. differences

poiseuille’s law applies only to the steady, laminar flow of newtonian fluids thru cylindrical tubes

Resistence to Flow

R = P/Q

Series resistence: R_T = R₁ + R₂ + R₃

Parallel resistence: 1/R_T = 1/R₁ + 1/R₂ + 1/R₃

Decrease flow of coronary arteries = decrease work in heart (coronary atherosclerosis)

Shear Stress: ratio of F:A