Download hemodynamics

Hemodynamics
Physics of Blood flow in the
circulation
Circulatory System
• Heart:
Has 2 collecting chambers - (Left, Right
Atria)
Has 2 Pumping chambers - (Left, Right
Ventricles)
Circulation Schematic
Left Side of Heart
Pulmonary Vein
A
Aorta
V
Aortic Valve
Mitral Valve
Tissues
Lungs
Tricuspid Valve
Pulmonary Valve
V
Pulmonary Artery
A
Right Side of Heart
Sup. & Inf. Vena Cava
Heart Valves
• Atrioventricular (A-V) valves - separate
Atria from Ventricles
• Bicuspid (Mitral) - Left Side
• Tricuspid - Right Side
• Semi-Lunar Valves - separate ventricles
from Arteries
Opening, Closing of Valves - Depends on Pressure
differences between blood
in adjacent areas
Heart Sounds
• ‘Lubb’ (1st sound) - Closure of A-V valves
• ‘Dupp’ (2nd sound) - Closure of S-L valves
Caused by Turbulence on closing.
Anything extra ’Murmur’ (swishing of blood)
Could be due to:
Increases
• Stenosis of Valves (calcification)
Pressure on
• Valves not closing properly
heart
(Incompetence, Insufficiency)
Heart Sounds and Phonocardiography
• Heart sounds are vibrations or sounds due to
the acceleration or deceleration of blood
during heart muscle contractions, whereas
murmurs (a type of heart sounds) are
considered vibrations or sounds due to
blood turbulence.
• Phonocardiographyis the recording of heart
sounds.
• Heart Sounds
– The auscultation of the heart provides valuable
information to the clinician concerning the
functional integrity of the heart.
Basic heart sounds
• The first heart sound is generated at the
termination of the atrial contractions, just at the
onset of ventricular contraction. This sounds is
generally attributed to movement of blood into
the ventricles, the artioventricular (AV) valves
closing, and the sudden cessation of blood flow in
the atria. Splitting of the first heart sound is
defined as an asynchronous closure of the
tricuspid and the mitral valves.
• The second heart sound is a low frequency
vibration associated with the closing of the
semilunar valves - the aortic and pulmonary
valves. This sound is coincident with the
completionof the T wave of the ECG.
• The third heart sound corresponds to the
sudden cessation of the ventricular
rapidfilling. This low-amplitude, low
frequency vibration is audible in children
and in some adults.
• The fourth heart sound occurs when the
atria contracts and propel blood into the
ventricles. This sound with very low
amplitude and low frequency is not audible,
but may be recorded by the
phonocardiography (PCG).
• The sources of most murmurs, developed
by turbulence in rapidly moving blood, are
known. Murmurs are common in children
during early systolic phase; they are
normally heard in nearly all adults after
exercise.
• Abnormal murmurs may caused by stenoses
and insufficiencies (leaks) at the aortic,
pulmonary, and mitral valves. They are
detected by noting the time of their
occurrence in the cardiac cycle and their
location at the time of measurement.
Auscultation and Stethoscopes
• Heart sounds travel through the body from the
heart and major blood vessels to the body surface.
• The physician can hear those sounds with a
stethoscope.
• Basic heart sounds occur mostly in the frequency
range of 20 to 200 Hz.
• Certain heart murmurs produce sounds in the
1000-Hz region, and some frequency components
exist down to 4 or 5 Hz.
• Some researchers even reported that heart sounds
and murmurs have small amplitudes with
frequencies as low as 0.1 Hz and as high as
2000Hz.
Stethoscopes: Historical and Current
• Has been used for almost 200 years, and still being
used nowadays for screening and diagnosis in
primary health care.
The typical frequency-response curve for a stethoscope
• Many types of electronic stethoscopes have been
proposed by engineers. These devices have
selectable frequency-response characteristics
ranging from the "ideal" flat-response case and
selected bandpass to typical mechanicalstethoscope responses.
• Physicians, however, have not generally accepted
these electronic stethoscopes, mainly because they
are unfamiliar with the sounds heard with them.
Their size, portability, convenience, and
resemblance to the mechanical one are other
important considerations.
Phonocardiography
• Phonocardiography is an mechano-electronic
recording technique of heart sounds and murmurs.
• It is valuable in that it not only eliminates the
subjective interpretation of these sounds, but also
makes possible an evaluation of the heart sounds
and murmurs with respect to the electrical (such as
ECG) and mechanical (carotid pulse recorded in
the midneck region) events in the cardiac cycle.
• It is also valuable in locating the sources of
various heart sounds.
• A PCG machine is usually consist of four
main parts:
–
–
–
–
A microphone or PCG transducer,
filtering (mechanical and electrical),
processing unit, and
display.
• There are optimal recording
sites for the various heart
sounds or PCG signals.
Because of the acoustical
properties of the transmission
path, heart sound waves are
attenuated but not reflected.
Figure shows four basic chest
locations at which the intensity
of sound from the four valves is
maximized.
• Auscultatory areas on the chest
A, aortic; P, pulmonary; T,
tricuspid; and M, mitral areas.
Blood Vessels
• Arteries
• Capillaries
• Veins
Systemic Pathway:
Left Ventricle
of Heart
Venules
Aorta
Arteries
Arterioles
Capillaries
Veins
Right Atrium
of Heart
Blood
• Composition:
– Approx 45% by Vol. Solid Components
» Red Blood Cells (12m x 2 m)
» White Cells
» Platelets
– Approx 55% Liquid (plasma)
» 91.5% of which is water
» 7% plasma proteins
» 1.5% other solutes
Blood Functions
• Transportation
of blood gases, nutrients, wastes
• Homeostasis (regulation)
of Ph, Body Temp, water content
• Protection
As a Result …….
• Blood behaves as a simple Newtonian
Fluid when flowing in blood vessels
i.e. Viscous stresses  Viscosity, strain rate
y
du
 
dy
No slip
at wall
u(y)
• Viscosity of Blood = 3 3.5 times of water
• Blood acts as a non-newtonian fluid in
smaller vessels (including capillaries)
Cardiac Output
• Flow of blood is usually measured in l/min
• Total amount of blood flowing through the
circulation = Cardiac Output (CO)
Cardiac Ouput = Stroke Vol. x Heart Rate
= 5 l/min
Influenced by Blood Pressure & Resistance
Force of blood
against vessel wall
 with water retention
 with dehydration, hemorrage
•Blood viscosity
•Vessel Length
•Vessel Elasticity
•Vasconstriction / Vasodilation
Overall
• Greater Pressure  Greater Blood
Differences
Flow
• Greater Resistance  Lesser Blood Flow

Blood Pressure
Driving force for blood flow is pressure
created by ventricular contraction
Elastic arterial walls expand and recoil
continuous blood flow
Blood pressure is highest in the arteries
and falls continuously . . .
Systolic pressure in Aorta: 120 mm Hg
Diastolic pressure in Aorta: 80 mm Hg
Typical values of circulatory pressures SP is the systolic pressure, DP the
diastolic pressure, and MP the mean pressure.
Ventricular pressure difficult to measure
arterial blood pressure assumed to indicate
driving pressure for blood flow
Arterial pressure is pulsatile
useful to have single value for driving pressure:
Mean Arterial Pressure
MAP = diastolic P + 1/3 pulse pressure
Pulse Pressure = systolic pressure - ??
= measure of amplitude of blood pressure
wave
MAP influenced by
• Cardiac output
• Peripheral resistance

MAP
CO x Rarterioles
• Blood volume
– fairly constant due to homeostatic mechanisms
(kidneys!!)
BP too low:
• Driving force for blood flow unable to
overcome gravity
O2 supply to brain 
 Symptoms?
BP too high:
• Weakening of arterial walls - Aneurysm
Risk of rupture & hemorrhage
Cerebral hemorrhage: ?
Rupture of major artery:
BP estimated by Sphygmomanometry
Auscultation of
brachial artery
with stethoscope
Laminar flow vs.
turbulent flow
Typical indirect blood-pressure measurement system The
sphygmomanometer cuff is inflated by a hand bulb to pressures above the
systolic level. Pressure is then slowly released, and blood flow under the
cuff is monitored by a microphone or stethoscope placed over a
downstream artery. The first Korotkoff sound detected indicates systolic
pressure, whereas the transition from muffling to silence brackets diastolic
pressure.
Principles of Sphygmomanometry
Cuff inflated until brachial artery compressed and blood
flow stopped
what kind of sound?
Slowly release pressure in cuff:
turbulent flow
Pressure at which . . .
. . . sound (= blood flow) first heard:
. . . sound disappeared:
Ultrasonic determination of blood pressure A compression cuff is placed
over the transmitting (8 MHz) and receiving (8 MHz ±D ƒ) crystals. The
opening and closing of the blood vessel are detected as the applied cuff
pressure is varied.
• Pressure can be stated in terms of column of
fluid.
mm Hg
50
100
200
300
400
Pressure Units
cm H2O
PSI
68
136
272
408
544
0.9
1.9
3.8
5.7
7.6
ATM
0.065
0.13
0.26
0.39
0.52
Pressure = Height x Density
or
P = gh
Density of blood
= 1.035 that of water
If Right Atrial pressure = 1 cm H2O in an open
column of blood
 Pressure in feet = 140 cm H2O
 Rupture
Incompetent venous valves
 Varicosities
 Venous Valves
Actual Pressure in foot
= 4-5 cm H2O
Pressures in the circulation
• Pressures in the arteries, veins and heart
chambers are the result of the pumping
action of the heart
• The right and left ventricles have similar
waveforms but different pressures
• The right and left atria also have similar
waveforms with pressures that are similar
but not identical
3. As blood enters the
aorta, the aortic pressure
begins to rise to form the
systolic pulse
4. As the LV pressure falls
in late systole the aortic
pressure falls until the LV
pressure is below the aortic
diastolic press.
2. Pressure rises until the
LV pressure exceeds the
aortic pressure
5. Then the aortic valve
closes and LV pressure falls
to LA pressure
 The blood begins to
move from the ventricle
to the aorta
1. The LV pressure begins
to rise after the QRS wave
of the ECG
•The first wave of atrial pressure (the A wave) is due to atrial
contraction
•The second wave of atrial pressure (the V wave) is due to
ventricular contraction
Normal Pressures
• RV and pulmonary systolic pressure are 12-15 mm
Hg
• Pulmonary diastolic pressure is 6-10 mm Hg
• LA pressure is difficult to measure because access
to the LA is not direct
AS produces a
pressure gradient
between the aorta
and LV
i.e. For blood to move
rapidly through a
narrowed aortic valve
orifice, the pressure
must be higher in the
ventricle
• The severity of AS is determined by the pressure drop across the aortic
valve or by the aortic valve area
• The high velocity of blood flow through the narrowed valve causes
turbulence and a characteristic murmur AS can be diagnosed with a
stethoscope
(a) Systolic pressure gradient (left ventricular-aortic pressure) across a
stenotic aortic valve. (b) Marked decrease in systolic pressure gradient
with insertion of an aortic ball valve.
Pressure Measurement
• Accurate pressure measurements are essential to
understanding the status of the circulation
• In 1733 Steven Hales connected a long glass tube
directly to the left femoral artery of a horse and
measured the height of a column of blood (8 feet,
3 inches) to determine mean BP
• Direct pressure measurements are made frequently
in the cardiac catheterization laboratory, the ICU
and the OR
• A tube is inserted into an artery and connected to
an electrical strain gauge that converts pressure
into force that is sensed electrically
• The output of the transducer is an electrical signal
that is amplified and recorded on a strip chart
• For correct pressure measurements the cannula
and transducer must be free of air, the cannula
should be stiff and short
Flush solution under pressure
Sensing
port
Sample and transducer
zero stopcock
Roller clamp
Electrical connector
Disposable pressure transducer with an integral flush device
Extravascular pressure-sensor system A catheter couples a flush solution
(heparinized saline) through a disposable pressure sensor with an integral
flush device to the sensing port. The three-way stopcock is used to take blood
samples and zero the pressure sensor.
Sensor
(a)
P
Diaphragm
Catheter
Liquid
Rc
Lc
Incremental
length
Rc
Lc
Rc
DV
Lc
Rs
Ls
(b)
Cc
Cc
Cc
Cs
C
d=
(a) Physical model of a catheter-sensor system. (b) Analogous electric
system for this catheter-sensor system. Each segment of the catheter has
its own resistance Rc, inertance Lc, and compliance Cc. In addition, the
sensor has resistor Rs, inertance, Ls, and
compliance Cs. The compliance of the diaphragm is Cd.
DV
DP