Chapter 7
Blood Pressure and Sound
• Blood Pressure
– Where : blood pressure in the 4 chambers of the
heart and in the peripheral vascular system
– Why : to help the physician determine the
functional integrity of the cardiovascular system
• Heart Sound
– What : fluctuations in pressure recorded over the
frequency range of hearing
– Where : vibrations set up by the accelerations
and decelerations of blood
Schematic Diagram of the
Circulatory System
Figure 7.1
Typical Values of Circulatory
Pressure
Figure 7.2 Typical values of circulatory pressures
Electrical conduction system
of the heart
SA node: P wave
AV node/Bundles: PR interval
Purkinje fibers/ventricular myocardium:
QRS complex
Ventricular repolarization: T wave
Correlation among heart
pressure, sound and ECG
Figure 7.15 Correlation of the four heart sounds with electric and
Mechanical events of the cardiac cycle.
7.1 DIRECT MEASUREMENTS
• Extravascular sensors
– Flushing Ssline-heparin solution to
prevent blood from clotting at the tip
– Catheter insertion : surgical cut-down or
percutaneous insertion
– Multiple-use vs disposable sensor
Unbonded Strain-Gauge
Pressure Sensor
(a) with increase pressure, the strain on
gage pair B & C is increased, while that
on gage pair A & D is decreased,
(b) Statham Pressure Transducer
P23XL
(a)
(b)
Figure 7.4 (a) Intravascular fiber-optic pressure
sensor
• Intravascular sensors
Mikro-Tip Pressure Catheter
Figure 7.5
Figure 7.4 (b) Characteristic curve
• Disposable pressure sensors
• Other types of pressure sensors
– passive-pressure endoradiosonde
(coupled LC element in a small flexible
box(high Q resonant circuit) ← changing
resonant frequency due to pressure
change ← detected by external
oscillator's resonant frequency
Passive-pressure endoradiosonde
7.2 HARMONIC ANAYSIS OF
BLOOD-PRESSURE WAVEFORMS
Harmonic Amplitude(%)
1 100
2 63.2
3 29.6
4 22.2
5 14.8
6 11.8
- -
Figure 7.6 The first six harmonics of the blood-pressure waveform
7.3 DYNAMIC PROPERTIES OF
PRESSURE-MEASUREMENT SYSTEMS
Fig. 7.7 Physical model and analogous
electric system of a catheter-sensor system
Simplification
① Cd >> Cc(noncompliant
catheter),
② Lc >> Ls, Rc >> Rs
(resistance and inertance
of the liquid in the sensor
can be neglected
compared to those of the
liquid in the catheter)
③ no air bubble (air bubble
effect→ Cb)
DefinitionLaminar or Poiseuille Flow
Case
3
2 3
( / ) or
( / ) or /
c c
c c
P PR Pa s m R
F A
P PL Pa s m L
dF dt aA
1d
d
VC
P E
4
2 2
8
or
c
c c
LR
r
m LL L
A r
Definition Circuit Element
Natural Undamped
Frequency(fn)
Damping Ratio()
1
21
( )2
r P
L V
1
2 c dL C1
23
4 ( / )( )L V P
r
1
2( )( )2
c d
c
R C
L
7.4 MEASUREMENT OF SYSTEM
RESPONSE
• transient step response : "pop"
technique
• sinusoidal frequency response :
sinusoidal pressure generator
Figure 7.11 Pressure-sensor transient response
7.5 EFFECTS OF SYSTEM
PARAMETERS ON RESPONSE
① air bubble : damped natural
frequency↓↓
② damped natural frequency ∝ 1/(length
of catheter)1/2
③ damped natural frequency ∝ inner
diameter of catheter
④ stiffer catheter : higher frequency
response
7.6 BANDWIDTH REQUIREMENTS
FOR MEASURING BLOOD PRESSURE
• "It is generally accepted that
harmonics of the blood-pressure
waveform higher than the tenth
may be ignored"
• Measurement of the derivative of the
pressure signal increase the
bandwidth requirements!
7.7 TYPICAL PRESSURE-
WAVEFORM DISTORTION
• overdamped : higher-frequency
components are attenuated.
• underdamped : higher-frequency
components are amplified, can be
transformed to overdamped by
catheter pinching
• catheter whip
7.8 SYSTEMS FOR MEASURING
VENOUS PRESSURE
• venous catheter → lower dynamic
range pressure sensor than arterial
measurements
7.9 HEART SOUND
•청진기(stethoscope) : 심음 과 폐음 의 청취
•심음도(phonocardiography)
•심음(heart sound)과 심잡음(murmur)
– heart sound : vibrations or sounds due to
acceleration or deceleration of blood
– murmur : vibrations or sounds due to blood
turbulence
• Auscultation technique
– sound wave attenuation : largest in the most
compressible tissue (lungs and fat layers)
– optimal recording sites for the various heart sound
• stethoscope
– propriety and convenience, portability
– variability in interpretation : user's auditory acuity
and training, techniques to apply stethoscope (firmly
applied chest piece : low frequency attenuation, loose
ear fitting)
– verbal description of sound : notoriously inadequate
• electronic stethoscope :
– selectable frequency response characteristics
including typical mechanical-stethoscope responses,
– not generally accepted mainly because unfamiliar
sound,
– other consideration : size, portability, convenience
resemblance to the mechanical stethoscope
5.10 PHONOCARDIOGRAPHY
• A recording of the heart sound and
murmurs : eliminate subjective
interpretation, evaluation heart sound
and murmur w.r.t. electric and
mechanical events in the cardiac cycle
(such as ECG, carotid arterial pulse,
juglar venous pulse, and apex
cardiogram-mechanical pulsation of
the heart muscle transmitted to the
body surface).
5.11 CARDIAC CATHETERIZATION
• Fluoroscopy + Catheterization
– imaging with radiopaque dye :
ventriculography, coronary arteriography,
aortography
– measurement, sample
– interventional radiology
• Swan-Ganz Catheter
•경피적 관상동맥 풍선 성형술(PTCA,
Percutaneous Transmural Coronary
Angioplasty)
The inflated balloon pulls the
catheter into the lung
Pressure waveform changes as a
catheter is inserted through the
heart into the lung.
• Valve Orifice Area Calculation:
Bernoulli's equation for frictionless flow
– 실제 상황에서는 마찰로 인한 손실이 발생하므로, 최소 혈류 면적은 개구 면적보다 작게 된다.
– cd는 discharge coefficient로서 0,6~0.85 이
다. 2
2
1 2
1
21 2
1
2
1 2
1
2
1 2
2
2
2( )
2( )
2( )
t
d
uP P gh
uP P
P Pu
FA F
u P P
F FA
u c P P
7.12 EFFECTS OF POTENTIAL AND KINETIC
ENERGY ON PRESSURE MEASUREMENTS
• static pressure effect : 혈압은 대기압에 대한상대치를 의미한다. 따라서 대기압의 변동에 따라 혈압의 절대치는 변하게 된다.
– 수중에서와 고산지대에서 심장의 부하는 각각 어떻게변할까?
– 상처가 난 경우 상처 부위를 높이 든 경우와 밑으로 내린 경우 통증의 차이는?
– 혈압 측정 시 센서의 위치는 어떠해야 할까?
• 도자를 통해 측정되는 압력의 종류– 측압(side pressure) : 혈압측정구가 유체의 흐름과수직인 경우
– 혈압측정구가 유체의 흐름과 평행인 경우 : +
additional kinetic energy ρu2/2
– 혈압측정구가 유체의 흐름과 반대방향으로 평행인 경우 : side pressure - ρu2/2
7.13 INDIRECT MEASUREMENTS
OF BLOOD PRESSURE
Fig. 7.20 Typical indirect blood-pressure measurement system.
Rica-Rocci Method
Korotkoff sound
Fig. 7.21 Ultrasonic determination of blood pressure
Fig. 7.22 The oscillometric method
Fig. 7.23 Block diagram of an
automatic NIBP device
7.14 TONOMETRY
• 기본원리 : 압력을 받고 있는 혈관이나 기관에 외부에서 압력을 가해 그 외벽이 평평해질 때, 이혈관이나 기관의 벽에 작용하던 circumferential
stress는 제거되고 내부와 외부의 압력이 같아짐을 이용하여 내부의 압력을 측정한다.
• 응 용 : 안압(intraoccular pressure)의 측정– 접촉식: applanation tonometer - apply a sensor
probe to the corneal surface, to measure the
force required to flatten a specific optically
determined area.
– 비접촉식 - using an air pulse linearly increasing
force deforms and flattens the central area of
the cornea and optical measuring the status of
the curvature of the cornea.
Fig. 7.24 Monitoring system for noncontact applanation tonometer.
Fig. 7.25 idealized model for an
arterial tonometer
Fig. 7.26 Multiple-element arterial
tonometer
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