This presentation describe application of biophysical laws in interpretation and principle of management of disease

1. Hemodynamics

2. Learning Objectives
• At the end of the lecture, students should be able to:
• Define the terms pressure, blood flow, velocity of blood flow
and resistance. and Describe the inter-relationship between
Resistance, flow and pressure.
• Describe streamline flow, turbulent flow, Reynold’s number
and cardiac murmurs.
• Explain the Poiseuille equation and its relevance to circulatory
system
• Define total peripheral resistance (TPR). Describe the factors
affecting total peripheral resistance.
• Describe the applications of law of Laplace in cardiovascular
physiology.

3. Function of CVS
ü Transport oxygen from the lungs to all body
cells
ü Provide nutrients and water from the
gastrointestinal system to all body cells
ü Transport stored nutrients from liver and
adipose tissue to all cells
ü Carries immune cells, antibodies, and clotting
proteins to wherever they are needed

4. Function of CVS
ü Remove metabolic wastes from all body cells to
kidney for excretion
ü Dissipation of heat from cells to skin
ü Exchange of carbon dioxide from body cells to
lungs for elimination
ü Transport particular toxic substances from some
cells to liver for processing

5. Hemodynamics
• Hemo+dynamics
• The study of the forces involved in the
circulation of blood
• Physical factors governing blood flow within
the circulatory system.
• Main factors are pressure, flow and resistance.

6. Basic Hemodynamic Principle [Ohm’s Law]
• Relationship between blood flow, vascular resistance
and blood pressure follow Ohm’s Law:
Q=ΔP/R
• Blood flow through a blood vessel is determined by
two factors:
• (1) pressure difference between the two ends of the
vessel, called "pressure gradient" [driving force that
pushes the blood through the vessel]
• (2) the impediment to blood flow through the vessel,
which is called vascular resistance

7. Pressure (P)
• Pressure: hydrostatic force
exerted on per unit area of the
vessel wall by the circulating
blood column,
• Expressed in mmHg.
• Normal mean blood pressure
is 100 mmHg

8. Pressure variations in circulation
Highest Pressure is systemic circulation is due to contraction of the
ventricles, gradually decreases as blood moves to vascular bed due to
resistance in the vasculature. Hence, pressure differs in every blood
vessel.

9. Resistance (R)
• Resistance is the opposition to fluid
movement in the blood vessel.
• Resistance increases as vessel
diameter decreases [ more friction
in small vessels.]
• the total resistance in the system is
calculated by adding the reciprocals
of the resistance provided by each
organ vascular bed [in parallel
circuit].
• Resistance[R]
= Pressure difference [P]/flow [Q]

10. Resistance & its determinants
• Resistance - major mechanism for changing
blood flow in the CVS
• Resistance changes from arteries to vein
maximum in the arterioles.
• Resistance is determined by three factors
–Length of Tube
–Viscosity of fluid
–Radius of the tube

11. Length of blood vessel
• Length show direct
relationship with
resistance
• More the length of
vessel, more will be
resistance to flow
• In CVS, length of vessel
is constant, hence
comparison with
different vessel is
possible

12. Blood Viscosity
• Measures internal resistance of
fluid during flow through vessel
• Viscosity is directly proportional
to resistance.
Resistance [R]α ν
• Increase in viscosity, resistance
will also increase
• In body fluid, blood viscosity is
more [due to presence of blood
cells] as compared to plasma.
• High viscosity= polycythemia
• Low viscosity= anemia

13. Radius of vessel
• Most important factor
in determining blood
flow
• Resistance is inversely
proportional to fourth
power of radius

14. Flow (Q)
• Flow (Q) is the volume flow rate of blood, and is
expressed as volume per time (e.g., ml/min).
• Depends on degree of resistance and pressure gradient.
• Flow[Q]=Pressure difference/Resistance [R]
• Important physical parameter to assess nutrient and
energy supply to the tissue

15. Effect of Pressure
Difference on
Blood Flow
If R=0 in both
vessels
Flow α ΔP

16. Velocity of Blood Flow
• Defined as rate of displacement of blood per unit
time.
Velocity of blood flow [v] = Q/A
where
• Q = Flow (mL/sec)
• A = Cross-sectional area (cm2)
• Flow (Q) is volume flow per unit time and is
expressed in units of volume per unit time (e.g., mL/
sec).
• Area (A) is the cross-sectional area of a blood vessel

17. Velocity of Blood Flow
• cardiac output of 5.5 L/min.
• The diameter of his aorta is 20 mm,
• total cross-sectional area of his systemic
capillaries is estimated to be 2500 cm2. What is
the velocity of blood flow in the aorta relative to
the velocity of blood flow in the capillaries?
• Calculate using formula
Velocity=Flow[Q]/Area[A]
velocity of blood flow is different according of cross-sectional area

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Effect of the diameter of the blood vessel on the
velocity of blood flow.

19. Problem solving
• Renal blood flow 500 mL/min.
• Arterial pressure as 100 mm Hg
• Renal venous pressure as 10 mm Hg.
• What is the vascular resistance

20. Calculating Peripheral Resistance
R = ∆P/Q
MAP=85 mm Hg
CVP=5 mm Hg
∆P=80 mm Hg
CO= 5L/min
R=?
Pulmonary Circulation:
Mean pulmonary artery pressure=15 mm Hg
Left atrial pressure=7 mm Hg
∆P=8 mm Hg
CO= 5L/min
R = ?
Systemic Circulation:

21. Problem solving
• Why Pulmonary Circulation is called low pressure
circulation while systemic circulation is called high
pressure circulation?
• In systemic circulation, venous pressure is 0 mmHg
while arterial pressure is 100 mmHg.
• In Pulmonary circulation, pulmonary artery pressure
is 16mmHg and Left atrial pressure is 2 mmHg
• Blood flow in both circulation is 100ml/sec.
• Which circulation has higher resistance?

22. Poiseuille Equation
• Poiseuille gave relationship between
resistance, blood vessel diameter (or radius),
and blood viscosity,
• Explains how the change in the radius of a
vessel affects its resistance, as well as flow
through blood vessel

23. Poiseuille’s Law
• If Length of vessel and viscosity of fluid is constant, than
Blood flow through the blood vessel is inversely
proportional to fourth power of radius of vessel.
• Small degree of change in vasoconstriction of blood vessel
would increase resistance several fold and greatly affect
blood flow.
• Example-
– 75% reduction in radius will lead to change 256 times change in
resistance
– Blood flow will also be affected fourth-power relationship between
resistance and vessel radius.

24. Poiseuille’s
Equation

25. Poiseuille’s Law
Q = π∆Pr4/ 8ηl or
R = 8ηl / πr4
Where : π/8 is a constant
Q = flow
R=resistance
∆P = the pressure driving force
r = radius of the vessel
η = viscosity of the fluid
l = length of the vessel

26. What are the implications of Poiseuille’s
Law ?

27. Poiseuille’s Equation
R = 8 ή L
π r4
Q = ΔP/R
R = ΔP/Q
Q = ΔP π r4
ή L 8
Where:
R = Resistance
ή = Viscosity of Blood
L = length of blood vessel
R4 = radius of blood vessel
raised to the 4th power

28. Types of Blood Flow
• Laminar: When velocity of blood flow is below a
critical speed, the flow is orderly and streamline
(This is the usual pattern of flow in the vascular system.)
• Turbulent: disorderly flow with eddies & vortices

29. Laminar flow
Laminar flow
ØLaminar flow –
blood flows in
streamlines with
each layer of
blood remaining
the same distance
from the wall

30. Laminar Flow

31. C, constriction;
A, anterograde;
R, retrograde
Turbulent Flow
Øblood flow in all
directions in the vessel
and continually mixes
within the vessel.
Øbecause of
Ø the velocity of blood
flow is too great,
Ø is passing by an
obstruction,
Ø making a sharp turn,
Ø passing over a rough
surface)

32. Turbulent flow
• The tendency for turbulent flow increases in direct proportion to
the velocity of blood flow, the diameter of the blood vessel, and the
density of the blood, and is inversely proportional to the viscosity
of the blood, in accordance with the following equation:
Re=(v.d.ρ)/ η
where Re is Reynolds' number and is the measure of the tendency
for turbulence to occur, ν is the mean velocity of blood flow (in
centimeters/second), d is the vessel diameter (in centimeters), ρ is
density, and η is the viscosity (in poise)
• When Reynolds’ number increases above about 2000 turbulent
flow will result

33. Parabolic velocity profile

34. Comparison of laminar flow to turbulent blood flow..
Parabolic
velocity
profile
Axial and
Radial Flow
• Laminar blood flow has a
parabolic profile ,with
velocity lowest at the
vessel wall and highest in
the center of the stream.
• Turbulent blood flow
exhibits axial and radial
flow.

35. Laminar Flow-
– all points in fluid move parallel to walls of tube
– Each layer of blood stays at same distance from
wall
– Blood cells forces to center of vessel
Turbulent Flow-
– At bifurcations of blood vessels
– Pressure drop greater than with laminar (square)
– Makes heart work harder
– Blood clots and thrombi much more likely to develop
– Produce more resistance
Characteristics

36. Effect of turbulence on pressure-
flow relationship
Turbulence
decreases flow
at any given
perfusion
pressure

37. Pressure-Flow Relationship
Reynolds's
Number
Dimensionless
number,
relates inertial
forces to
viscous forces
Reynold’s Number = density * diameter * mean velocity

38. Compliance of blood vessels
• Compliance is change in volume of
blood contained in a vessel for a given
change in pressure.
• C = V/P
• C = Compliance or capacitance (mL/
mm Hg)
• V = Volume (mL)
P = Pressure (mm Hg)
• higher the compliance of a vessel, the
more volume it can hold at a given
pressure.

39. Gravity and Pressure
ü Pressure fall from supine to standing
posture due to [immediate] effect of
gravity which includes:
ü Venous pressure in increases
ü Blood pooling in vein
ü Cardiac output decreases
ü Normal MAP is 100 mm Hg, which
is equivalent to a column of blood
about 4.5 feet high.
ü Changing in posture to standing,
Blood pressure at the level of the
head reduce to 60-70 mm Hg due to
the effects of gravity.

40. Gravity and Blood Pressure
ü Gravity also affects blood pressure below
the heart when we are standing.
ü Blood pressure increases below the heart in
proportion to the distance that it falls.
ü In a typical adult, blood pressure in arteries
in the feet is ~170 mm Hg when standing.

41. Systemic
Circulation-
Comprised of
Parallel and
Series Circuits

42. • In CVS, arrangement of blood vessels supplying organ
or tissue are of two types
• In Series: illustrated within a given organ.
– supplied with blood by a major artery and drained
by a major vein.
– Within the organ, blood flows from the major artery
to smaller arteries, to arterioles, to capillaries, to
venules, to veins.
– The total resistance equals to sum of the
individual resistances
Series Circuits

43. The resistance measured in
arteries, arteriole, venules
and vein of alveoli are:
R1=5
R2=10
R3=2
R4=1
What will be the total
resistance ?
Total R= R1+R2+R3+R4

44. Parallel Circuits
• illustrated by the distribution of blood flow among the
various major arteries of the aorta to various organ
system (e.g., renal, cerebral, and coronary).
• Venous blood is collected by major veins and finally
drained to heart.
• Total resistance in a parallel arrangement is less
than any of the individual resistances.

45. If different values of
resistance is major arteries of
aorta supplying various
organ =
R1= 2
R2= 5
R3= 10
R4= 20
R5= 50
1/Rtotal = 1/R1 + 1/R2 + 1/R3 + 1/R4 +1/R5
1/Rtotal = 1/2 + 1/5 + 1/10 + 1/20 +1/50 = 0.77
Rtotal = 1.29 RU (resistance units)

46. Arrangements of blood vessels in series and in parallel.
Arrows show direction of blood flow. R=Resistance

47. Difference
Series circuit
• Total flow is constant at
each level in the series,
• the pressure decreases
progressively as blood
flows through each
sequential component
Parallel circuit
• the flow through each organ is a
fraction of the total blood flow,
• no loss of pressure in the major
arteries and that mean pressure
will be approximately the same
• adding a resistance to the circuit
causes total resistance to
decrease.
• Increase in resistance of one of
the individual vessels in a parallel
arrangement= total resistance
increases

48. Problem solving
• If branches of Aorta offers resistance to
Kidney, Lungs and Liver =1/10 each, what
will be total resistance?
• If aorta added supply to spleen by another
artery having resistance 1/10, what will be
total resistance encounter by blood flow
from aorta.

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Arterial Pressure Pulse
• Pulse pressure can be used as an
indicator of stroke volume
because of the relationships
between pressure, volume, and
compliance
• pulse pressure will change if
stroke volume changes,
• or if the compliance of the
arteries changes.
• Several pathologic conditions
alter the arterial pressure curve
in a predictable way e.g.
Arteriosclerosis, Aortic
stenosis, Aortic regurgitation

50. Factors Affecting Pulse Pressure?
Arterial compliance can be approximated by the relation:
C = ΔV/ΔP or ΔP = ΔV/C
ΔV=stroke volume and ΔP=pulse pressure
Or
pulse pressure ~ stroke volume/C
Above relationship reveals :
• decrease in compliance will result in an increase in
pulse pressure.
• Increase in Stroke volume will increase Pulse pressure
provided no other changes occur in vascular bed.

51. Law of LaPlace
Vessels are “built to
withstand the wall
tensions they normally
“see”
If intravascular
pressure increases,
will increase vessel
wall tension (T)
In response,
vascular smooth
muscle contracts
and T returns to
normal

52. Law of LaPlace
The law of Laplace states that the force of tension (T)
exerted on the wall of the blood vessel is directly
proportional to the pressure (P) within the vessel and the
radius (R) of the vessel but opposed by thickness.
Where T = tension in the vessel wall
∆P = Transmural pressure
r = radius of the vessel
m = wall thickness
May explain critical closing pressure
T = (∆P*r) / m

53. Law of LaPlace- Relevance
• For given BP, increasing the radius of the vessel
leads to a increase in tension.
• Arteries must have thicker walls than veins
because they carry much higher BP.
• Capillaries also carry significant BP, but unlike
arteries, capillary walls are thin. Small size leads
to reduced level of tension so thick walls not
needed.
• Conclusions: Properties of this relationship helps
us understand the variable thickness of arteries,
veins, and capillaries.

54. Physiological Implications of the
Physics of Circulation
ü During aging, compliance in the large arteries decreases.
ü Since pulse pressure = stroke volume/C, a 20% decrease in arterial
compliance would result in a 20% increase in pulse pressure.
ü The larger transients in blood pressure in the elderly have been
shown to be an important cardiovascular risk factor.
ü The pulse pressure amplification with aging is due to large artery
stiffening. Different factors may contribute to this stiffening; for
example, a decreased connective tissue elasticity, atherosclerosis and
a decrease in smooth muscle relaxation.

55. End of lecture
•Thanks