Chapter 13

Blood Pressure Monitoring

Originates from the heart

Value depends on 3 factors:

cardiac output

diameter of arteries

the quantity of blood

Commonly refers to arterial blood pressure

peripheralresistance

One of the oldest physiological measurements

Powerful risk factor for cardiovascular disease

Circulation System

AV valve close

Aortic valve close

Circulation System

Definition

단위 면적의 혈관벽에 가해지는 혈액의 힘continuous : 혈액순환에 있어서 가장 중요함 심장에서 pumping 된 양과 같은 양의 혈액이 인체 각 부분에 전달되어야 함

Why do we need BP?

1) 혈관 질환이나 생리학적 불균형을 알 수 있음2) cardiac output 의 변화 , 혈관저항의 변화 , 혈류역학 및 생리학적 변화의 영향을 반영3) 말초신경 계통의 변화상태를 판단

혈압의 종류1) 수축기 혈압 (systolic BP)

2) 이완기 혈압 (diastolic BP)

3) 평균 혈압 (mean BP)

3

210

diastolicsystolicpdt

TMean

T

Blood Pressure

Brachial artery is the most common measurement site Close to heart Convenient measurement

Other sites are :forearm / radial arterywrist (tends to give higher SP)

The most common indirect methods areAuscultation and Oscillometric

Measurement of Blood Pressure

Invasive (Direct)

측정위치 : brachial, carotid, femoral 정맥압 (CVP, central venous pressure) 동맥압 (RAP, right atrial pressure)

Catheter 의 특성이 중요 as short as possible as stiff as possible

Noninvasive (Indirect)

Use of Korotkoff sound Sphygmomanometer

(cuff, pressure gage, pressure bulb, release valve)

+

sthethoscope

Measurement of Blood Pressure

Use of Korotkoff sound

1906 년 Russian Physicist Korotkoff : 5 phase of korotkoff sound (400 – 500Hz)I - V : first appearance of sound - silence

장점 : safe (no side effect) easy to measure

단점 : not accurate not continuous difference between observers instrument error (incorrect size of cuff)

Cuff size

AHA (american heart association) cuff width = 40% of the arm circumference bladder length = should cover 80% of the arm circumference 3mmHg/sec of slope

thin cuff width : high BP, wide cuff width : low BP

Indirect Measurement

The Korotkoff sounds are auscultated with a stethoscope or microphone (automatic measurement)

Korotkoff sounds are generated by the flow of blood and vibrations of the vessel

The frequency range of Korotkoff is 15~500 Hz and the accuracy is ± 2mmHg (SP) and ±4mmHg (DP)

Korotkoff Method

SP and DP are estimated from the amplitudes of the oscillation by using a (proprietary) empirical algorithm.

The cuff pressure is deflated either linearly or stepwise.

The intra-arterial pulsation is transmitted via cuff to transducer

Oscillometric Method

Photoplethysmography (PPG)

Tonometry

Ultrasound

Other Noninvasive Methods

Components

1) Catheter - semi rigid (filled with saline)

- 압력을 측정하는 부위까지 삽입 (balloon tipped catheter)

2) Pressure transducer

3) Monitor

장점 : continuous observation, sampling blood

단점 : technical problems (air bubble, infection)

Direct Measurement

Extravascular sensor Intravascular sensor

Direct Measurement

Direct Measurement

Catheter Model and Fluid Resistance

4

8

r

lRC

fRp C

Flow of fluid in a catheter, ,

is proportional to the pressure difference,

21 ppp

:

fp

Riv

CR Resistance of the tube

(friction between the fluid and the inside surface

of the tube)

:l

:r radius of the tube

viscosity of the fluid

length of the tube

Inertance and Compliance

Inertance ( 유체의 관성 )

Compliance ( 벽의 탄성 )

t

tC

fdtC

P0

1

Volume of expansion 시간당 흐름의 변화를 감지

dt

dfLP C

constant

t

tfdtvol

0p

volCC

Fluid-Electrical Analogy

Catheter Equivalent Circuit

22 r

L

A

mLC

dt

diLv

:

:l

:r radius of the tube

viscosity of the fluid

length of the tube

VOLCC 151053.0

t

tidt

Cv

0

1

Frequency Response of a Catheter with a Diaphragm

ACT

MEASP P

PG

DCCC

DCP

CCffLjR

CCfjG

21

2

21

Example #1

Catheter length : 2 meterRadius : 0.46 mmWall with zero complianceDiaphragm compliance : Nm /1004.2 515

2/001.0 mNs

CC

51043 /10374.111046.0/2001.08 mNsRC

36232 1033.121046.0 mlrVOL

3/1 cmg (water)

9233 10008.31046.0/210 CL

Compliance of the water in the catheter,

NmmlCC /10704.033.11053.0 51515

mlmmlmVOL 33.1/101033.1 3636

Example #2

DCCC

DC

ACT

MEASP

CCffLjR

CCfj

P

PG

21

2

21

Compute the transfer gain, PG

dBGP 34.4

8.173

Catheter with Pinch, Bubble, and Leak

Pinch

Bubble

Leak

NmVOLC BB /1002.1 58

4

8

p

pP

r

lR

PCEQ RRR

2p

pP

r

lL

Assumption

Pinch is a cylindrical shapeCompliance of the pinch is neglected as a small

quantity

llp

H

HH F

PR

Pressure differenceinside and outside the catheter

CBDEQ CCCC

EQH

EQ

H

EQEQ

EQH

EQ

H

ACT

MEASP

fCj

R

fCjR

fLjR

fCj

R

fCjR

P

PG

2

22

2

2

Example #3

Example #1Pinch that reduces the radius by one-half

It has a length

Calculate pinch compliance, resistance, and frequency response,

cml p 1

PG

5943

/10099.91023.0

01.0001.08mNsRP

623

3

102.601023.0

01.010

PL