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