1. The document discusses key concepts related to cardiovascular hemodynamics including blood flow, blood pressure, vascular resistance and compliance, and laminar versus turbulent flow. 2. It defines compliance as the change in blood vessel volume from a change in pressure, and explains that veins have greater compliance than arteries. Vascular resistance depends on vessel diameter and affects blood flow based on Ohm's Law. 3. The document also discusses laminar versus turbulent blood flow, using the Reynolds number to characterize the transition between the two states. Turbulent flow requires more energy to maintain blood flow.

2. 2
Biophysics of
cardiovascular
system
HEMODYNAMIC PRINCIPLES
MAGDI AWAD SASI

3. Circulation
 Your body
resembles a large
roadmap, There
are routes or
“arteries” that take
you downtown to
the “heart” of the
city.

4. 4
Lecture outline
• Define vascular distensibility ,vascular compliance ,discuss
factors affecting it and relate it to PR and ABP.
• Discuss factors affecting vascular compliance.
• Define law of laplace and discuss its application in human CVS
• Describe the procedure of hiss test and account for the
possible results.
• Describe laminar and turbulent blood flow and account for
such turbulence.
• Define Renaulds number and relate its values to different types
of blood flow.
• Define peripheral resistance ,mention factors affecting it and
discuss the mechanisms underlying such effects.
• Discuss the effects of PR and ABP.

5. 3 Major Parts of the Circulatory system
Blood Vessels - routes blood travels.
Heart – pumps or pushes blood through
body.
Blood – carries important “ *stuff ” through
body.
•* Stuff – includes oxygen, food, & waste

6. # 1 Blood Vessels : One Way Streets
Blood Vessels
resemble very
long and skinny
tunnels that are all
through your body.

7. The Structure of Blood Vessels
Types of Arteries
• Elastic arteries:
• Largest
• Closest to heart
• Stretch during systole
• Recoil during diastole
• Muscular arteries
• Systemic circulation
• Arterioles
• Tiny branches of small arteries
• Feeders of capillary networks

8. Elastic (conducting)
arteries
• High pressure
• Thick muscle
• Near heart
• Thick walls
• More elastic fiber,
less smooth muscle
• Lose elasticity with
aging
Vessel Structure – Elastic Arteries

9. Vessel Structure - Elastic Arteries
Aorta and elastic arteries
• Can vasoconstrict or
vasodilate
• Large arteries expand,
absorb pressure wave then
release it with elastic recoil
- Windkessel effect
• Help to push blood along
during diastole
• With aging have less
expansion and recoil

10. Muscular
(distributing) arteries
• Deliver blood to
organs
• More smooth
muscle
• Less elastic fibers
Vessel Structure – Muscular Arteries

11. Arterioles
• Distribution of blood
in organs
• Composition varies
depending on position
- more muscle, less
elasticity nearer heart
• Regulate flow from
arteries to capillaries
• Flow = ΔP/R
• vary resistance by
changing vessels
size
• Site of blood pressure
regulation
Vessel Structure - Arterioles

12. The Structure of Blood Vessels
Properties of Veins
• Collect blood from capillaries
• Merge into medium-sized veins
• Merge then into large veins
• Blood pressure is low here
• Valves keep blood flowing toward the heart

13. 3
Veins
Volume reservoir- “capacitance vessels” (60-70%) of
blood
Have vasomotor control.
Valves in abdominal veins prevent backflow
Skeletal muscle “pump” and respiratory pump

14. Hemodynamics
Hemodynamics can be defined as the
physical factors that govern blood flow.
These are the same physical factors that
govern the flow of any fluid, and are based
on a fundamental law of physics, namely
Ohm's Law
It states that current (I) equals the voltage
difference (ΔV) divided by resistance (R).

15. Circulatory Physiology
Factors Affecting
Blood Flow
• Pressure
• Flow goes up as
pressure
difference goes up
• Flow goes from
higher to lower
pressure
• Regulated by
nervous and
endocrine
systems
• Peripheral resistance
• Flow goes down as
resistance goes up

16. Functional properties of
different blood vessels
1. Artery:
Aorta and large artery
Pressure reservoir vessels

17. Compliance : How much the vessel’s volume changes as the
intraluminal pressure changes (at equilibrium).
C = compliance,
DV = change in blood volume due to …
DP = change in blood pressure.
Distensibility: compliance relative to some initial state (at
equilibrium).
Vi = initial blood volume
D = distensibility,

18. Vascular Distensibility
= is the fractional increase in volume for each mmHg rise in pressure times original
volume-( veins are 8x more distensible)
0 mmHg 100 mmHg
Artery
Vein 800 ml
100 ml
In hemodynamics, it’s more valuable to know the total quantity of blood that can
be stored in a given portion of the circulation for each mmHg pressure rise.
Capacitance = increase in volume/increase in pressure
The capacitance of veins is 24 times that of arteries.

19. The ability of a blood vessel wall to expand and contract
passively with changes in pressure is an important
function of large arteries and veins.
This ability of a vessel to distend and increase volume with
increasing transmural pressure (inside minus outside
pressure) is quantified as vessel compliance (C),
which is the change in volume (ΔV) divided by the change in
pressure (ΔP).

21. Compliance of blood vessels
C = compliance (mL/mm Hg)
V = volume (mL)
P = pressure (mm Hg)
C = ∆V/ ∆P
• Compliance is a slope
• At low pressures, veins
have a greater compliance
than arteries
• At high pressures,
compliance is similar in
veins and arteries (but
volume is much greater in
veins)

23. First, the slope, which represents the compliance at a given pressure,
decreases as pressure increases because the blood vessel wall is a
heterogeneous tissue. Therefore, compliance decreases at higher
pressures and volumes (i.e., vessels become "stiffer" at higher
pressures and volumes).
Second, at lower pressures (venous pressure is usually less than 15
mmHg), the compliance of a vein is about 10 to 20-times greater than
an artery.
Therefore, veins can accommodate a large changes in blood volume
with only a small change in pressure. The greater compliance of veins
is largely the result of vein collapse that occurs at pressures less than
10 mmHg. At higher pressures and volumes, venous compliance
(slope of compliance curve) is similar to arterial compliance. This
characteristic makes veins suitable for use as arterial by-pass grafts.

24. Compliance changes related to vasocontraction or aging
With vasocontraction:
• Venous volume
decreases and pressure
increases
• Venous compliance
decreases
Similar effects in arteries with aging

25.  There is no single compliance curve for a blood vessel.
1. Vascular smooth muscle contraction
2. Conversely, smooth muscle relaxation increases compliance .
This is particularly important in the venous vasculature for the
regulation of venous pressure and cardiac preload.
 Another example of changing compliance is reduced aortic
compliance with age or disease (e.g., arteriosclerosis). When this
occurs, there is a qualitatively similar downward shift in the
compliance curve for the aorta. Such compliance changes in the
aorta are responsible in large part for the increase in aortic
pulse pressure with advanced age or arterial disease.

26. Distribution of blood within the circulatory system at rest:

27. The Distribution of Blood in the Cardiovascular System
0167

28. A Comparison of a Typical Artery and a Typical Vein
8

29. Compared to veins, arteries
• Have thicker walls
• Have more smooth muscle and elastic fibers
• Are more resilient
Differences between arteries and veins
9

30. Middle artery:
carry blood to arterioles
distribution vessels
Small artery and arteriole:
resistance vessels are regulated
by neurohumoral factors
Control of capillary blood flow

31. 3. Venous Vessels, capacitance
vessels: large vein, vena cava.
 Blood reservoir
 big compliance
1.Low mean venous pressure
2.Low resistance vessels
3.Venous valve
4.Venule .

32. Circulatory Physiology
Key Note:
Blood flow is the goal. Total peripheral
blood flow is equal to cardiac output.
Blood pressure is needed to overcome
friction to sustain blood flow. If blood
pressure is too low, vessels collapse,
blood flow stops, and tissues die; if too
high, vessel walls stiffen and capillary
beds may rupture.

33. 3
Ohm’s Law
Q=∆P/R
Flow (Q) through a blood
vessel is determined by:
1) The pressure difference
(∆P) between the two ends
of the vessel
• Directly related to flow
2) Resistance (R) of the
vessel
• Inversely related to flow

34. Cardiovascular Regulation
Factors Affecting Tissue Blood Flow
• Cardiac output
• Peripheral resistance
• Blood pressure

35. Blood Flow (L/min)
Blood flow is the quantity of
blood that passes a given point
in the circulation in a given
period of time.
Unit of blood flow is usually
expressed as milliliters (ml) or
Liters (L) per minute.
Overall flow in the circulation of
an adult is 5 liters/min which is
the cardiac output.
CO= HR X SV
70 b/min x 70 ml/beat
=4900ml/min

36. P1-P2
(1). F = ————
R
(2). Poiseulle’s law for
laminar flow.
πΔpr4
F = ————
8ηL

37. 7
Mechanical properties of blood
vessels
Laplace law – mechanical
stress of blood vessel walls
is directly proportional to
the pressure and vessel
radius
Tension T in walls of some blood vessels:
vessel r(m) p(kPa) T(N.m-1
)
aorta 0.012 13 156
artery 0.005 12 60
capillary 6 x 10-6
4 0.024
vein 0.005 2 10
vena cava 0.015 1.3 20

38. 8
Elastic and muscular blood vessels
Aorta behaves
like typical
elastic vessel
Arterioles are
muscular
vessels able of
vasodilatation
and
vasoconstriction

39. Windkessel Vessel --- Aorta and big
arteries.
Contain a large amount of elastic tissue besides the
smooth muscle.
Transiently store blood during systole, and then shrink
to produce onward blood flow during diastole.

40. 0
Blood Pressure—
The driving force
Stephen Hales
1733
Blood pressure (hydrostatic
pressure) is the force exerted
by the blood against any unit
area of vessel wall.
Measured in millimeters of
mercury (mmHg). A pressure of
100 mmHg means the force of
blood was sufficient to push a
column of mercury 100mm
high.
All vessels have it – but
we’re usually addressing
arteries when we refer to it.

41. contracted
Ejected Blood
When the LV contracts more blood enters
the arterial system than gets pushed
onward. This causes the arteries to stretch
and pressure within them to rise. The
highest pressure achieved is known as the
systolic pressure.

42. relaxed
Recoil of the elastic
artery
As the LV relaxes, the stretched arterial walls recoil
and push the contained blood onward through the
system. As they recoil, the amount of blood
contained decreases as does pressure. The lowest
pressure achieved just before the next contraction
is the diastolic pressure.

43. Laminar flow
Velocity of different layers is different
 Parabolic
 No vibration
 No sound

44. Types of Blood Flow
Normal Disturbed Flow

45. Laminar Flow
Laminar flow is the normal condition for blood flow
throughout most of the circulatory system.
It is characterized by concentric layers of blood
moving in parallel down the length of a blood vessel.
The highest velocity (Vmax) is found in the center of the
vessel.
The lowest velocity (V=0) is found along the vessel
wall.
The flow profile is parabolic once laminar flow is fully
developed. This occurs in long, straight blood
vessels, under steady flow conditions.
5

47. One practical implication of parabolic,
laminar flow is that when flow velocity
is measured using a Doppler flowmeter,
the velocity value represents the
average velocity of a cross-section of
the vessel, not the maximal velocity
found in the center of the flow stream.

48. Laminar flow and Turbulence
Laminar flow is
parabolic, highest
velocity in center (least
resistance), lowest
adjacent to vessel walls
Turbulent flow is
disoriented, no longer
parabolic, energy
wasted, thus more
pressure required to
drive blood flow.
quiet
noisy

49. blood flow is in direct proportion
to square root of pressure
difference
 Vibration
 Sound (murmur)
 Wasteful energy
Turbulent flow

50. Turbulent Flow
Generally in the body, blood flow is laminar.
However, under conditions of high flow, particularly
in the ascending aorta, laminar flow can be
disrupted and become turbulent.
When this occurs, blood does not flow linearly and
smoothly in adjacent layers, but instead the flow
can be described as being chaotic.
Turbulent flow also occurs in :
1. Large arteries at branch points
2. Diseased and narrowed (stenotic) arteries
3. Across stenotic heart valves.

51. Turbulence
It increases the energy required to drive blood flow
because turbulence increases the loss of energy in
the form of friction, which generates heat.
When plotting a pressure-flow relationship ,turbulence increases
the perfusion pressure required to drive a given flow.
Alternatively, at a given perfusion pressure, turbulence leads to a
decrease in flow.

52. Turbulence does not begin to occur until the
velocity of flow becomes high enough that
the flow lamina break apart.
Instead, turbulence occurs when a critical
Reynolds number (Re) is exceeded.

53. •Where
•v = mean velocity,
• D = vessel diameter,
• ρ = blood density, and
•η = blood viscosity
NR< 2000
laminar flow
NR> 3000
turbulent flow

54. Re increases as velocity increases, and decreases as viscosity
increases.
Therefore, high velocities and low blood viscosity (as occurs with
anemia due to reduced hematocrit) are more likely to cause
turbulence.
An increase in diameter without a change in velocity also
increases Re and the likelihood of turbulence; however, the
velocity in vessels ordinarily decreases disproportionately as
diameter increases.
The reason for this is that flow (F) equals the product of mean
velocity (V) times cross-sectional area (A), and area is
proportionate to radius squared; therefore, the velocity at
constant flow is inversely related to radius (or diameter)
squared.
For example, if radius (or diameter) is doubled, the velocity
decreases to one-fourth its normal value, and Re decreases by
one-half.

55. Under ideal conditions (e.g., long,
straight, smooth blood vessels), the
critical Re is relatively high. However, in
branching vessels, or in vessels with
atherosclerotic plaques protruding into
the lumen, the critical Re is much lower
so that there can be turbulence even at
normal physiological flow velocities.

56. Blood flow in blood vessels
The differences between
theoretical and real flow rate
profiles are given mainly by
the fact that blood is a non-
Newtonian liquid and is
influenced by the
distensibility and
compliance of the vessel
wall..
The flow rate profile changes during pulse wave.
We can obtain important diagnostic information from
values of blood velocity and the shape of the flow rate
curve.

57. 57
Blood flow in an obstructed blood
vessel
Fig. after Cameron
et al., 1999
The upper curve represents blood flow in a vessel without atherosclerotic
stenosis (narrowing), the lower one in a vessel with stenosis.
We need bigger increase of pressure ∆p for the same increase in blood
flow ∆Q (volume per time unit).

58. 8
Pressure in individual segments of blood circulation

59. Circulatory Physiology
• Control of Peripheral Resistance
– Consists of three components:
• Vascular resistance
– Goes up as diameter is reduced
– Arteriole diameter dominates
• Viscosity of blood
– Depends on hematocrit
• Turbulence
– Cause of pathological sounds

60. How Would a Decrease in Vascular Resistance
Affect Blood Flow?
FLOW = ∆P
RESISTANCE
FLOW = ∆P
RESISTANCE
Conversely,
Therefore, flow and resistance are inversely related!
• Resistance is the impediment
to blood flow in a vessel.
• Can not be measured directly
Resistance
R = ΔP = mmHg
Q ml/min

61. Resistance of the cardiovascular system opposes
the movement of blood
For blood to flow, the pressure gradient must
overcome total peripheral resistance
• Peripheral resistance (PR) is the resistance of the
arterial system.
Resistance (R)
1

62. Resistance makes a difference for the two sides of the heart!
Let’s say the CO (flow) is roughly
100ml/sec (easier math).
To calculate systemic resistance vs.
pulmonary resistance we need to know
pressure differences.
Pulmonary resistance is 16-2/100
Systemic resistance is 100/100
So, CO is same on each side of heart
(has to be!), but right side generates
less pressure due to lower resistance
(1/7th than systemic).
16
mmHg
2mmHg
100 mmHg
0mmHg
R = ΔP = mmHg
Q ml/min

63. Factors of Resistance
Poiseuille’s Law = Q =_π∆Pr4
8ηl
Blood viscosity
Total vessel length
Vessel diameter
• Resistance ∝ (length)(viscosity)
(radius)4

64. Resistance to blood flow:
P1-P2 8η1
F = ——— R = ———
R πr4
Resistance comes from external
friction (L, r) ,internal friction (η).
Total peripheral resistance is mainly
determined by arterioles(60 ～ 70%).

65. Resistance and arterial blood
pressure affect blood flow of
organ and redistribution of
blood flow of organs

66. 66
Resistance
•resistance = 8 x η x L
• π x r4
• where:
• η = viscosity (“eta” mostly depends on hematocrit)
• L = length of vessel
• r = radius of vessel
• conclusion:
• the body regulates blood flow by altering vessel radius
• halving the radius → 16x resistance

67. 67
Peripheral resistance of blood
vessels
•Low vascular impedance
characteristic for brain, liver,
spleen and kidney arteries
•High vascular impedance
characteristic for arteries of
skeletal muscles

68. 68
Peripheral resistance of blood
vessels
• Percentage of total peripheral resistance
estimated for individual segments of blood
circulation:
 arteries ......... 66 %
 (among those arterioles 40 %)
 capillaries ........ 27 %
 veins ............. 7 %
• In vasodilatation, R decreases – heart load
decreases
• In vasoconstriction, R increases – heart load
increases