Medical and health care

1. HEMODYNAMICS
Hemodynamics is the study of blood flow.
A solid understanding of normal and
abnormal blood flow is an important skill
for anyone doing Doppler ultrasound.

2. Arterial Vessels
There are four major types of vessels in the arterial
system:
1. Large elastic arteries
2. Smaller muscular arteries
3. Arterioles
4. Capillaries
The large elastic arteries are the arteries close to the
heart. These include the aorta, the brachiocephalic, the
carotids and the subclavian arteries. They are called
elastic arteries because the middle layer of their walls
contains a significant amount of elastic tissue. This gives
these arteries the ability to stretch and recoil when they
receive a bolus of blood from the heart.

3. Smaller Muscular
Arteries
As we move further out into the arterial
system, the arteries become smaller and also
more muscular.
Examples of these arteries include the
axillary, femoral, and popliteal arteries

4. Arterioles
Moving more distally the arteries continue to
become smaller and smaller and more and more
muscular. Just before the capillary bed we will
encounter the tiny arterioles. These vessels are the
“gatekeepers” of the arterial system. They regulate
the blood flow to the tissues.
Their walls consist essentially of a thin intimal
inner layer surrounded by a layer of smooth
muscle. This gives these vessels the ability to
actively vasodilate or vasoconstrict depending on
the body’s requirements. This arteriolar function
plays a key role in arterial hemodynamics.

5. Resistance
The primary factors affecting the
resistance to fluid flow are:
The length of the vessel
The viscosity of the fluid
The radius of the vessel

6. Arterial Resistance Beds
types:
1. Low resistance beds
2. High resistance beds
3. Very high resistance beds

7. The resistance to flow in each type of
bed is determined by the arterioles
that lie between the arteries and the
capillaries.

8. When needed, arterioles can
vasodilate to significantly increase
t h e i r d i a m e t e r s . T h i s l o w e r s
resistance and promotes forward
flow.
C o n v e r s e l y , a r t e r i o l e s c a n
vasoconstrict to reduce their
diameters, increase resistance, and
reduce forward flow

10. Low Resistance Beds
In low resistance vascular beds the
arterioles are dilated. This means
there is little resistance to flow, and
there is good forward flow in both
systole and diastole.

11. Some examples of organs with low
resistance vascular beds include the
brain, kidneys, liver, spleen, gravid
uterus, active ovary, and testes.

12. High Resistance Beds
In high resistance beds the arterioles
are more constricted. This increases
resistance to flow.
Some examples of organs with high
resistance beds include the fasting gut
(small and large bowel), non-active
ovary, non-gravid uterus, and smaller
muscular beds.

13. Very High Resistance Beds
In very high resistance beds the arterioles
are significantly constricted.. In a very
high resistance bed, the resistance to flow
is so high there is usually a short
component of reversed (retrograde) flow
in early diastole
Good examples of very high resistance
beds are the large resting muscular beds
such as the resting legs or the resting arms.

14. Low Resistance Flow

15. The Doppler sonographer should
look for this pattern: a steep, almost
vertical, acceleration to peak systole,
and a more gradual deceleration
following peak systole.

19. Normal Laminar Flow
Inside normal arteries blood flows in layers
called laminae, with each layer of blood sliding
over the adjacent layer. This is called laminar
flow, and it occurs in both large and small
arteries.
the fastest laminae are in found in the centre of
the vessel and the slowest are closest to the wall.

21. Laminar Flow. This type of flow
profile occurs in both normal large
and small arteries.

23. The change in velocity across the
lumen of the artery is called the
velocity profile.
Normal laminar flow has two types
of velocity profiles: plug and
parabolic

24. Plug Flow
Plug flow is seen in large arteries. As a
result, the vast majority of the laminar flow
at a similar speed, with only the layers close
to the wall moving more slowly. This type of
laminar flow is called plug or blunt flow
because of the blunt shape of the velocity
profile.

25. Plug Flow. This type of flow profile
is found in large arteries.

27. Parabolic Flow
In smaller arteries,
In this type of laminar flow, the fastest
laminae are in the centre of the vessel, and the
adjacent laminae move more slowly. This
produces a steeper velocity profile that is
called parabolic flow.

28. Parabolic Flow. This type of flow
profile is found in smaller arteries.

30. Systolic Window
A systolic window is a normal finding in the
arterial waveforms of large arteries. The term
“systolic window” describes the clear triangular
area in the systolic component of the arterial
waveform.
It is seen in the normal waveform of large arteries
because of the plug flow in these vessels.

31. Systolic Window. Note the clear
area below the systolic envelope.

33. Spectral Broadening
Spectral broadening refers to fill-in of the systolic
window. The clear triangular systolic window is
not seen due to the wide range of Doppler shifts
that are displayed throughout systole.
In large arteries, spectral broadening is an
abnormal finding indicating that the blood is not
flowing in its normal “plug” laminar fashion.
The appearance of spectral broadening in a large
artery should raise a red flag for the sonographer.

34. In smaller arteries spectral broadening is a
normal finding. The normal parabolic
laminar profile in these vessels generates a
wide range of Doppler shifts throughout
systole.

35. Two other causes for artificial spectral broadening
are using a sample volume that is too large, or
positioning the sample volume at the edge of the
vessel close to the boundary layer.

36. Disturbed Laminar Flow
Disturbed laminar flow describes laminar flow
in which the laminae waver are unstable. This
can result in a greater range of velocities from
the different laminae.

37. Disturbed
Laminar Flow

38. Disturbed laminar flow occurs naturally at
the bifurcation of normal arteries. The
carotid bulb is a good example.
In large arteries, disturbed laminar flow
due to atherosclerotic plaque is a
common cause for spectral broadening.

40. Turbulent Flow
Turbulent flow is non-laminar flow.
Turbulent flow is not disturbed flow. It is
not even severely disturbed flow. It is
completely different! There are no laminae
in turbulent flow.
In Turbulent flow, blood flows in all
directions: forward, backward (retrograde),
and sideways.

41. Turbulent Flow

42. Turbulence is not a normal feature
of blood flow in any artery.
It only occurs when the blood is
moving at significantly increased
velocities, such as those found in
the region of a high grade arterial
stenosis.

43. On the spectral display, turbulence is indicated by
bidirectional flow in systole. Bidirectional flow is
flow that is moving in opposite directions at the
same time.
If you are sampling turbulent flow, you should
see a negative component below the baseline in
systole as the sample volume detects the negative
shifts from the blood that is moving backwards.

44. Turbulence. Evidence of turbulence on the other side of the
baseline in a high grade stenosis.

45. Plz Comment?
Here’s a waveform from the origin of the main
renal artery. What are your thoughts?

47. Diagnosis
1. Significantly increased peak systolic and end diastolic
velocities.
2. Bidirectional flow in systole consistent with turbulence.
3.Spectral Broadening
.

49. Stenosis