Hemodynamics

Velocity and Flow

- Q (flow) = V (linear velocity) X A (x-sectional area)
- As AÝ , Vß or Aß , VÝ
- Used to estimate aortic valve area and press (velocity)
- A
_{1}V_{1}= A_{2}V_{2}continuity equation - with onset of aortic stenosis, area decreased and pressure (velocity) increased

Velocity and Pressure

- v = 100 cm/s 200cm/s 100cm/s
- KE=1/2pv
^{2}= 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__:- quiet, smooth, requires less energy
__turbulent flow__:- high velocity, large diameter, high density, low viscosity
- Reynold’s number:
- Rc = Vdr / h V = vel; d = diamtr; r = dens; h = viscosity
- When > 200, laminar Þ turbulent
- turbulence identification
- feel or palpate neck for frill (vibration)
- can hear as a murmur
- can hear bruit Þ turbulence in neck; why?
- Atherosclerosis Þ narrowing Þ bruit
- Complete obstruction Þ no bruit
- Abdominal aortic anyuerysm Þ dilated artery which may produce eddy currents Þ bruit

Pressure and Flow

- Hagen – Poiseuille law
- D P = 8 l Q h / p r
^{4 } - 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}= R_{1}+ R_{2}+ R_{3} - Parallel resistence: 1/R
_{T}= 1/R_{1}+ 1/R_{2}+ 1/R_{3} - Decrease flow of coronary arteries = decrease work in heart (coronary atherosclerosis)
**Shear Stress**: ratio of F:A