Vascular Ultrasound. Fluid Hemodynamics. Fluid Hemodynamics. Blood flow influenced by Cardiac function Elasticity of the vessel Tone of vascular smooth muscle Dimension, pattern and interconnection of branching vessels. Fluid Hemodynamics.
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Blood flow influenced by
- High energy
- High pressure
- Low energy
- Low pressure
The large volume of blood entering the
arterial reservoir is responsible for the
high energy level.
The function of the heart and blood
vessels is normally regulated to maintain
volume and pressure in the arteries within
the limits required for smooth function.
To achieve this there must be a balance
between the amount of blood that enters
and the amount of blood that leaves the
Flow to all the body tissues is adjusted according to
the tissues’ particular need at that instance.
Main form is Potential Energy
As the hydrostatic pressure increases:
Flow in which blood moves in concentric
Loss of energy during blood flow is:
Describes flow in a cylindrical tube model. The
mean linear velocity of laminar flow is
V α(P1- P2) x r2
V = Mean linear velocity
Q = V x CSA = V x pr2
Q a (P1- P2) x r2 x pr2 = p (P1- P2) x r4
L h 8Lh
8Lh = P1- P2
R = P1- P2
Q = P1- P2
Resistance to flow is influenced by the presence of
numerous interconnected vessels.
Vessels in series:
RT = R1 + R2 + R 3 + …………….. Rn
Vessels in parallel:
1 = 1 + 1 + 1 + ………. 1
RT R1 R2 R3 Rn
Thus the contribution of any single vessel to the total
resistance of a vascular bed, or the effect of a change in
the dimension of a vessel, depends on the presence and
relative size of the other vessels linked in series or
Occurs due to
The factors that affect the development of
turbulence are expressed by the dimensionless
Reynolds number (Re):
Re = vq2r
h = viscosity
q = density
r = radius of the tube
v = velocity
- stroke volume.
- pressure wave.
Cardiac contraction leads to:
The shape and amplitude are affected by
An increase in any of these factors
will lead to an increase in the pulse
amplitude and the systolic pressure
Systolic Amplification is due to
- changes in vessel diameter
- dividing branches
Small and Medium arteries
Minute arteries, arterioles and capillaries
Reversal of flow due to
Pressure gradient between two arteries
changes due to difference in the
of the pressure wave.
Whether a hemodynamic abnormality result
from a stenosis and how severe it may be
Other changes distal to the stenosis include
Blood flow can be normal in the presence
of severe stenosis due to:
Resting blood flow decreases only
The inability for an increase in blood flow during exercise is due to the fact that the sum of the resistances of the obstructions (stenosis, collateral resistance, or both) and the peripheral resistance prevent a normal increase in flow.
Proximal to the stenosis
At to the stenosis
Distal to the stenosis