Download Blood Pressure, Flow and Sound

Blood Pressure,, Flow and Sound
Hsiao Lung Chan,
Hsiao-Lung
Chan Ph.D.
Ph D
Dept Electrical Engineering
Ch
Chang
Gung
G
University, Taiwan
[email protected]
Outline






Circulatory system
Heart sounds and measurements
Blood pressure and measurements
Cardiac output
FLowmeter
Plethymography
Lecture edited by 詹曉龍, 長庚大學電機系, 2010.
HL Chan , EE, CGU
Blood Pressure 2
Simplified circulatory system
Deoxygenated
blood
Oxygenated
blood
Upper body
Lung
Right
atrium
Left
atrium
Right
ventricle
Left
ventricle
Lower body
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Blood Pressure 3
Circulatory system
Systemic
circulatory system
Pulmonary
circulatory system
Systemic
circulatory system
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Cardiac cycle
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Blood Pressure 5
Systemic and pulmonary circulation
Systemic circulation
aortic
ti valve
l close
l
A.V . open
2  CO2
left atrium    
 left ventricle   tissue O

 right atrium
mitral valve open
M .V . close
Pulmonary circulation
pulmonary
l
valve
l close
l
P .V . open
 O2
right atrium     
 right ventricle   lung CO
2 
 left atrium
tricuspid valve open
T .V . close
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Systolic and diasystolic periods

Systolic period


The ventricular muscle is contracting to pump blood into
aortic artery or pulmonary
pulmonary, so the blood can be pulsatile to
tissue or lung.
Diasystolic period

The atrium muscle is contracting to pump blood into
ventricle, and the blood is stored in ventricle.
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Heart sounds


Analysis of the second
heart sound to evaluate
the stiffness of aortic
valve
Existence of systolic
murmur means the aortic
valve is stenosis
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Auscultatory areas
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Stethoscopes




Mohrin, 1995
Bell mode
 two
t
openings
i
off th
the
diaphragms coincide with
each other
Diaphragm mdoe
 No through opening
Ph i i
Physicians
can change
h
mode
d by
b
pressing chestpiece against a
patient’s body and twisting the
bell housing
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Blood Pressure 10
Stethoscopes (cont
(cont.))


High-frequency sounds, or murmurs, are easier to hear
with the diaphragm.
Th bell
The
b ll, which
hi h should
h ld be
b applied
li d lightly
li htl to
t the
th chest,
h t
transmits low-frequency sounds more
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Blood Pressure 11
Frequency response of stethoscopes
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Blood Pressure 12
Piezoelectric microphone
1
v
C
t1
0
1
idt 
C
t1
0
K
dx
x
dt  K
dt
C
R
Electrode
C
vo
charge
amplifier
Highpass filtering: passes frequencies higher than the corner
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frequency fc = 1/(2RC).
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Blood pressure
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Indirect blood pressure measurement
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Indirect blood pressure measurement
Cuff
Occluded
blood vessel
( Korotkoff sounds )
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Blood Pressure 16
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Direct blood pressure measurement
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
Extravascular sensors
Intravascular sensors
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Extravascular blood pressure measurement
Saline-heparin solution
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Strain-gage
Strain
gage blood pressure sensor
Plastic dome
Armature
Fluid
couplings
li
Flexible diaphram
Rigid frame
Cable
Strain guages
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Strain guage
displacement
displacement
l  A  (l  l ) Astretched
R 
R 
 (l   l )
Astretched
 2 l
A


 l
A

 (l   l ) 2
lA

 l
A

 (l 2  2ll  l 2  l 2 )
Al
2 l
R
l
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Blood Pressure 21
Wheatstone bridge circuit
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Intravascular sensors

Detection of pressure in the catheter tip without the use of
liquid-coupling system



Bonding strain-gage
strain gage systems onto a flexible diaphragm at
catheter tip

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High-frequency
Hi
hf
response
Eliminate time delay
Temperature and electric drift,
drift fragility,
fragility nondestructive
sterilization
Expensive
p
Fiber-optic microtip sensor
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Blood Pressure 23
Fiber-optic pressure sensor
Coupling between LED source and
detector is a function of overlap of
two acceptance angles
l on the
h
pressure-sensor membrane
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Blood Pressure 24
Fiber optics
Snell’s law
n2 sin  2  n1 sin 1
Refraction of rays that
escape from wall of fiber
Low refractory index
High refractory index
n1=1.62 for a glass
3 : accepted
angle
l for
f internal
i t
l
reflection in fiber
Internal reflection
within a fiber
when n1 sin  ic  n2 sin 90 0  n2
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Fiber-optic pressure transducer:
can be used for magnetic resonance imaging
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Pressure-waveform
Pressure
waveform distortion
Presence of larger air bubble pr
blood cot in catheter tip
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Pressure-waveform
Pressure
waveform distortion (cont
(cont.))
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Harmonic analysis of blood
blood-pressure
pressure waveform
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Cardiac catherterization
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Cardiac catherterization (cont
(cont.))


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
Aided by x-ray equipment
Measure pressures within each chamber of the heart and
across the
th valves.
l
Measure cardiac output
Measure oxygen concentration across valves and walls
(septa) of the heart
C
Coronary
arteries
t i can be
b viewed
i
d by
b injecting
i j ti dye
d or
opened using balloon angioplasty
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Pressure gradient
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Areas of valve orifice
P1  P2 
u 2
2



A   F


2
(
P

P
)
 1 2 
F
1/ 2
F : Flow
F
A
c2





2
(
P

P
)
 1 2 
1/ 2
Consider losses by friction,
discharge coefficients cd is added
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Blood Pressure 33
Example of computing area of aortic valve
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Relative continuous blood pressure measurement

Arterial Tonometer
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Arterial tonometer
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Multiple-element
Multiple
element arterial tonometer
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Cardiac output


Cardiac output (CO) = heart rate (HR)  stroke volume
(SV)
E
Example
l

Stroke volume
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Average resting heart rate

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Volume of ejected blood from the ventricles (about 80 mL/beat)
70 beats/min
Cardiac output
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
= 80  70 = 5,600 mL/min = 5.6 L/min
CO is regulated by changes in both HR and SV.
Heavy exercise increases both HR and SV, and CO can increase
to as high as 25 L/min.
L/min
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Blood Pressure 38
Methods for measuring cardiac output
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Blood Pressure 39
Fick method
dm dt
CO 
Ca  C v

dm/dt
/ is consumption
p
of O2 ((liters/min)
/
)


The rate of inhalation or exhalation of gas is measured using
the spirometer
Ca and Cv are concentration of O2 (liters/liter) measured by
obtaining samples from any artery and from pulmonary
artery
t
separately
t l ((using
i blood-O
bl d O2 analyzer)
l
)
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Blood Pressure 40
Fick method example
A patient’s O2 concentration, measured in the pulmonary
artery, is 0.12 L/L. The O2 concentration measured in the
patient’s aorta is 0.19
0 19 L/L.
L/L A spirometer is used to obtain
the patient’s O2 consumption rate 0.250 L/min. Calculate
the patient’s
patient s cardiac output.
Ans:
Ca = 0.19 L/L, Cv = 0.12 L/L and dm/dt = 0.250 L/min

dm dt
0.250 L/min
CO 

 3.57 L/min
/
C a  C v 0.19 L/L  0.12 L/L
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Blood Pressure 41
Dye dilution




A smallll quantity off dye
d is injected
d into venous blood
bl d
stream through a catheter tip.
The dye passes through heart
heart, and is mixed with blood
blood.
The dye then appears in the arterial circulation.
Arterial blood is drawn off through
g another catheter and
concentration of dye is measured through an optical
densitometer.
Th di
The
disadvantages
d
t
off the
th d
dye dilution
dil ti
 Not completely nontoxic
 Dye cannot be removed immediately from the blood
stream, thus repeat measurements are difficult to
perform
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Blood Pressure 42
Rapid-injection
Rapid
injection indicator-dilution
indicator dilution curve
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Blood Pressure 43
Thermodilution




A thermodilution
h
dl
pulmonary
l
artery catheter(known
h
(k
as the
h
Swan–Ganz catheter) is inserted
A bolus (10 ml) of room temperature,
temperature or iced (00C) 5%
dextrose in water or 0.9% cool NaCl is injected through
catheter into right atrium
Drop in temperature in arterial circulation is measured
using a thermistor attached to a catheter in pulmonary
artery.
artery
Advantage


Lower temperature bolus can be rapidly warmed to body
temperature.
Repeat measurements are easier to perform.
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Blood Pressure 44
Thermodilution curve

If cardiac output is reduced, the bolus takes longer to pass through
the heart.
 Healthy patients with normal cardiac output have less area under
temperature versus time curve, than unhealthy patients with some
type of
o coronary
co o a y insufficiency.
su c e cy
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Blood Pressure 45
Bioimpedance measurement
T
Two
or four
f
electrodes
l t d
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Four-electrode
Four
electrode impedance plethysmography
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Bioimpedance measurement
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Impedance plethysmography
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Impedance plethysmography (cont
(cont.))
Zb 
b L
A
V  L A 
 b L2
Zb
Z2
Z 
Z 
Z  Zb
Z  Zb
Z Zb
Z2
Zb 
Z
because Z  Z b
  b L2 Z
 V 
Z2
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Blood Pressure 50
Minnesota impedance cardiography
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Blood Pressure 51
Thoracic impedance parallel
parallel-column
column model
Constant tissue
impedance
such as bones,
muscles, fat
L2
dZ
SV   2 LVET
Z0
dt max
Pulsatile
P
l til blood
bl d
volume change
LVET, left ventricular ejection time
, resistivity
y of blood
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Blood Pressure 52
Features of dZ/dt
Aortic
valve open
Aortic
valve
l close
l
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Blood Pressure 53
Thoracic impedance measurement using four
electrodes
0.5-4
0
5 4 mA RMS,
RMS
50-100 kHz
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Blood Pressure 54
Improved impedance cardiography by spectrogram
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Blood Pressure 55
dZ/dt
Spectrogram
Low-frequency
distribution
Detection of these peaks
enable noise-resistant
estimation of LVET
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Blood Pressure 56
Bioimpedance cardiac output versus thermodilution
cardiac output in 842 data pairs in 68 ICU patients.
r2=0.74 (p<0.001)
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Blood Pressure 57
Cardiac output monitor
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Blood Pressure 58
Blood flow



Physical factors that influence blood flow are pressure and
resistance
Fl
Flow
th
through
h arterial
t i l grafts
ft iis measured
d att the
th time
ti
off
surgery to ensure that the graft has been successfully
inserted
Flow in peripheral blood vessels is measured as an aid in
the diagnosis of peripheral vascular disease
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Blood Pressure 59
Blood flow rate



Volume of blood moving past a fixed point per unit time
F = P/R (mL/min)
where P, pressure; R, resistance
Poiseuille’s law
R = 8L/r4
where L = length,  = viscosity, r = radius
F = Pr4/(8L)
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Blood Pressure 60
Measurement of blood flow





Dye dilution, invasive method
Transcutaneous electromagetic flowmeter
Ultrasonic Doppler flowmetry
Magnetic resonance imaging (MRI) to measure blood flow,
though promising, is in its infancy
f
Positron emission tomography (PET) has proved useful in
th evaluation
the
l ti off llocall blood
bl d flow,
fl
especially
i ll in
i the
th brain,
b i
but remains expensive
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Blood Pressure 61
Electromagnetic flowmeter
L1
e   u  B  dL
0
B= magnetic flux density
L= length between electrodes
u =instantaneous
instantaneous velocity of blood
Flow = u•A
where A is cross-sectional area of vessel
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Blood Pressure 62
Flowmeter at catheter tip
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Blood Pressure 63
Perivascular probe
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Blood Pressure 64
Continuous-wave
Continuous
wave ultrasonic Doppler flowmetry

Measurement of volume flow requires


Cross-sectional area of the vessel (which can be obtained
from the B
B-mode
mode image)
Mean of the velocity profile.
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Blood Pressure 65
Frequency range of ultrasound
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Blood Pressure 66
Physics of ultrasound

Wavelength and period
Pascal (Pa,
newton/m2)
sound velocity c  f  
tissue
resolution
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Blood Pressure 67
Doppler effect
2v cos 
fd 
f
c
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Blood Pressure 68
Color Doppler


Structures (usually blood) are
moving towards or away from
the p
probe,, and its relative
velocity
By calculating frequency shift of
a particular sample volume
volume, its
speed and direction can be
determined and visualized
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Blood Pressure 69
Doppler ultrasound flowmeter
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Blood Pressure 70
Doppler ultrasound flowmeter (cont
(cont.))
D
Doppler
l effect
ff t
Bl d cells
Blood
ll to
t from
f
reflecting
fl ti targets
t
t
fd u

f0 c
fd
2u
2u


f0 c  u
c
where
here f0 = source
so rce frequency
freq enc
fd = Doppler frequency shift
u = target velocity
c = velocity of ultrasound
Considering the angle factor
2 f 0u cos 
fd 
c
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Blood Pressure 71
Doppler ultrasound flowmeter (cont
(cont.))
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Blood Pressure 72
Color Doppler in Echocardiography
A mid-muscular ventricular septal defect.
Colors are used to represent the velocity and direction of blood flow.
flow
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Blood Pressure 73
Cardiac output estimation by Doppler utrasound

SV = BV  LVET  A



BV, average blood velocity in aorta during systole
A, cross-sectional area of aorta
CO = SV  HR
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Blood Pressure 74
Reference





John G. Webster, Medical Instrumentation, application and
design, 3rd Ed., Houghton Mifflin, 2000.
J h G.
John
G Webster,
W b t Bioinstrumentation,
Bi i t
t ti
JJohn
h Wiley
Wil & Sons,
S
2003.
John Enderle,
Enderle Susan Blanchard
Blanchard, Joseph Bronzino,
Bronzino
Introduction to Biomedical Engineering, Academic Press,
2000.
Joseph J. Carr, John M. Brown, Introduction to Biomedical
q p
Technology,
gy, Pearson Education,, 2000.
Equipment
生物醫學工程導論，滄海書局，2008.
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Blood Pressure 75