Medical Instrumentation II

Chap 7. Blood pressure and sound

1. Blood pressure : Invasive blood pressure

Non-invasive blood pressure

2. Intraocular pressure : Tonometry

3. StethoscopeMedical Instrumentation II

1. Tonometry

Medical Instrumentation II

P

M

P

M

Contact Area = A

F = Mg(We Known

factor)

F

Ball Ball

AFP /Force per unit Area

• Measurement structure

Medical Instrumentation II

LED

PhotoSens

orEx) Photo diode & Photo Transistor

Intraocular

pressure

2. NIBP

Medical Instrumentation II

Cuff pressure

Cuff

Spuit

Stethoscope

• Heart structure

Medical Instrumentation II

Pulmonary Vein

Aorta

Pulmonary artrySuperi

or

Inferior

Venacava

Coronary vein

Coronary

artery

- Systemic circulation- Pulmonary circulation- Coronary circulation

• Blood pressure graph

Medical Instrumentation II

120mmHg

90mmHg

Systolic pressure

Diastolic pressure

NIBP measure the value of systolic & diastolic pressure. Also It isn’t the print graph

• About PCB (Printed Circuit Board)

Medical Instrumentation II

PCB is Classified MLB(Multi layer Board), Double substrate 1. Spec2. Circuit design3. CAD : schematic

(OrCAD)4. CAD : layout(OrCAD)5. PCB produce6. Components apply7. Test & programming8. Debugging

• Automatic Blood pressure graph & principle

Medical Instrumentation II

P

80mmHg

120mmHg

Blue is pressurize

Red is decompress

Cuff pressure decrease

-2 ~ -3 mmHg / sec

Cuff > inner vessel

Systolic

pressure

Diastolic

pressure

Medical Instrumentation II

• Blood pressure sound graph

NoiseHeart sound

graph

Osillometric

Method

3. Invasive BP measurement

Medical Instrumentation II

Dome Diaphragm

Strain gage

Cable

Diaphragm is flexible

Pi

Po

Blood vessel

Saline

• Catheter

Medical Instrumentation II

1. Length2. Diameter3. Material4. Air bubble in

Catheter

Catheter have several trouble!!!

Pi(t) Po(t)

t t

≠

Equivalent circuit model of catheter – sensor system Voltage, v, [V] Pressure,

P, [pa] Current, i, [A=C/s] Moving

flow, f, [m³/s] Charge, q, [C] Volume,

v, [m³]

Medical Instrumentation II

EX)

(Center of Mass )

M F = Mg

A

Air potentia

l

m f = mg

Hight ↑ Pressure ↓

Medical Instrumentation II

Dome Diaphragm

Strain gage

Cable

Pi

Po

Blood vessel

Saline

• Apply measurement

Length is applied resistor,

Capacitor and Conductor

Pi & Po is applied voltages

Blood flow is applied

Current

1. Resistance

Riv

A

L

i

vR

A

L

EX)

P1

P2

Medical Instrumentation II

Pipe represent Resistor.

As length & diameter.

R

PPkF 21

2. Capacitance of compliance

Medical Instrumentation II

dt

dvCi

dt

dPCf YC

Young’s

modulus

Pressure is increasing,

Compliance is increasing

Medical Instrumentation II

3. Inductance / Inertance

dt

diLv

dt

dfLP

2A

mL

Mass is increasing, innersure is increasing,And inductance is increasingAs a result, current flow (di/dt) is decreasing.