Salman Bin AbdulAziz University

College of Applied Medical Sciences

Pr Ridha BenSalah 1 BMIS 471 Biomedical Electronic Instruments - 1

Biomedical Electronic

Instrumentation I: BMIS 471

Prof. Ridha Ben Salah

Biomedical Electronic Instruments 1: BMIS 471

Pr R. Ben Salah 2

Programme

Chapter 1: Electro-physiology and biomedical signals

Chapter 2: Biomedical electronic circuits

Chapter 3: Electrocardiography

Chapter 4: Electroencephalography

Chapter 5: Electronic Filter Design

BMIS 471 Biomedical Electronic Instruments - 1

Biomedical Electronic Instruments 1

Pr R. Ben Salah 3

Chapter 1

Electro-physiology and biomedical signals

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 4

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

Bioelectric signals represent often the majority of biomedical signals. These

signals proceed from electric activity of cells which may be on activity or one

pause state.

1. Electric dipole

Definition : Electric dipole is the whole of two electrical charges +q and –q

(q>0) separated by a distance d ǂ 0.

A B

-q o +q

d

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 5

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

Chapter 1. Electrophysiology and

bioemedical signal

Dipole Moment

is an unit vector is exprimed on C.m or on debye. (1 debye = 0.33. 10-29 Cm)

Potential of electrical dipole

M

H

α

A B

O

MA = rA MB = rB OM = r AB = d (d << r)

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 6

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

Electric potential created by the dipole is :

(ε is the permitivity of the vacuum)

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 7

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potentiel

3. Rest potentiel and action potentiel

4. Biomedical signals

2. Nernst potential

Let us consider the following experiences :

Experience 1 : Two separated compartments I and II containing respectively two

solutions S1 and S2.

V

M1 M2

KCl

S1 (C1) S2 (C2)

M1 and M2, two Zinc electrodes are immerged respectively in I and II.

S1 and S2 are two ZnSO4 solutions. C1 and C2 are they concentration

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 8

Chapter 1 Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

2. Nernst potential

We can note a potential V on the voltmeter

Interpretation:

Regarding NERNST formula we can write :

V1 = V(M,S1) and V2 = V(M2,S2) are respectively the potential between (M1,

S1) et (M2, S2)

E0 : the normal potential R : the ideal gas constant

Z : valence of the Zinc T : absolute temperature

F : Faraday constant

C1 = C2 =

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 9

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

Remarque (Universal constants)

Number of Avogadro NA =6.02×10 23 MOL−1

Speed of light (vacuum) C = 3x108 MS−1

Planck constant h = 6.63×10 − 34 JS

Charge of the electron e = 1.602×10 − 19 C

Faraday constant F = 96500 Cmol − 1

The ideal gas constant R = 8.32 mol− 1 K − 1

Boltzmann constant k = 1.38×10 − 23 J K − 1

Potential difference between the two compartments is :

The potential difference between S1 and S2 is :

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 10

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potentiel

3. Rest potentiel and action potentiel

4. Biomedical signals

Experience 2 : we consider a compartment with two solution S1 and S2

separated by a dialysis membrane and two electrodes M1 and M2.

We can see that V =0

M1 M2

S1 (C1) S2 (C2)

Interpretation :

V = V (M2) – V(M1) = V(M2) – V(S2) + V(S2) - V(S1) + V(S1) – V(M1) = 0

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 11

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

V = V (M1) – V(M2) = [V(M2) – V(S2)] + [V(S2) – V(S1)] – [V(M1) – V(S1)] = 0

V = V2 + [V(S2) – V(S1)] – V1 = 0

V(S2) – V(S1) = - (V2 – V1) = - =

Vm = V(S2) – V(S1) =

Vm is called membrane potential or DONNAN potential

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 12

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

3. Rest potentiel and action potentiel

A cell or nerve membrane have potential Vm

Vm = Vext – Vint

At a rest state (Nernst Formula) :

On average Vm = 70 mV.

+

+

+ +

+

+ +

_ _

_

_ _

_ _ _

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 13

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

3. Rest potentiel and action potentiel

3.1. Rest (balance) Potential

If we excite a membrane by a extra electrical impulse , there is an increase in

Vint and a decrease in Vext therefore. Vm decreases at a minimum, then returns

to equilibrium V0. This describes the variation of the rest potentiel.

Vc : Critical potential - +

0 t

Vc = 55 mV

V0 = 70 mV

Vm = Vext – Vint

+

+

+ +

+

+ +

_ _

_

_ _

_ _ _

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 14

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

3.2. Action potential

c

0 t 0 t

Vc b d

V0 a e

f g

Vm Vm

Action potential Action potential (Cardiac)

(nervous and muscle fibre) (cardiac fibre)

ab : pre-potential

bcd : Spike

de : post-potential negative efg : post-potential positive

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah

15

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4. Biomedical signals

4.1 Introduction

Acquisition and processing of biomedical signals is not very easy

because of the weakness of the BS amplitude (some mv and even

some microvolt). Frecency spectral is often very limited (very low

frequency signals). For the design of BS we have to observe some

precaution.

It is very essential to take care to the electrical security of the

patient and the medical personnel during the acquisition of biomedical

signals

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah

16

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

There are several types of biomedical signals : bioelectric, bioimpedance, bioacoustic,

biomecanic, biooptic ….

4.2. Bioelectric signals

There are different types of bioelectric signal with cells or nervous origins:

Heart bioelectric signal : electrocardiogram (ECG)

Brain bioelectric signal : electroencephalogram (EEG)

Muscle bioelectric signal : electromyogram (EMG)

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah

17

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4.3. Bioimpedance signals

Bioimpedance signal is detected as following :

Biomedical impedance is generated by the injection of an electric courant

within high frequency (3 khz to 1 Mhz) and low amplitude (1 mA) by the

means of two electrodes. The acquisition of biomedical signal is performed

using two other electrodes. This bioimpedance signal called also elecrtical

plethysmogram shows impedance variation of explored corporel segment.

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 5

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4.4. Bioacoustic signals

The activity of many organs creates some acoustic sounds which may be

detected by the mean of piezoelectric sensors. For example :

The phonocardiogram (PCG) : linked to cardiac sounds

The Doppler signal : due to the pulsatil circulation of the blood in the big

vessels

The microphonic signal : detected at the level of the cochlea (inner ear)

The flow of air can involve sounds which may be stored.

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah

19

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4.5. Biomechanic signals

Biomechanic signals are generated by mechanical action of the fluid

circulation. And specially the blood when going through cardiac cavities and

circulatory system. For example : Aortic pression, ventricular pression …

These signals are often detected by invasive (or blooding) methods because

we must be very near of the organ which created these signals (in situ)

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 7

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4.6. Biooptic signals

Detection of several physiologic signals is based on using light springs. These

biooptic signals could resulted from photonic excitation of the retina for

example. Here are some examples of biooptic signals :

Visual-retinal signal

Some signal obtained by fibroscopy or endoscopy

Spectroscopy in vivo (inner the body) and in vitro (in the lab) can give

informations about certain solids, liquids or gaz into the explored organ and

specially the blood

Signals obtained by using optical density principle for the determination of

albumine and globuline concentration (elctrophorese of the blood))

BMIS 471 Biomedical Electronic Instruments - 1

Pr R. Ben Salah 21

Chapter 1. Electrophysiology and

bioemedical signal

1. Electric dipole

2. Nernst potential

3. Rest potential and action potential

4. Biomedical signals

4.7. Characteristics of biomedical signal

Signals Amplitude Frequency Origin form

ECG Electrocardiogram

1 - 10 mV 0.05 –140 Hz Heart

EEG

Electroencephalogram

2 – 100 μV 0.5 – 100 Hz Brain

EMG

Electromyogram

1 – 5 mV 5Hz–500 Hz Muscle

PCG

phonocardiogram

1 – 5 mV 25 – 1 KHz Heart B1 B2 B1

CBI

Cardiac Bioimpedance

5 – 10 mV 0.5 – 30 Hz Heart

ERG

Electroretinogram

0.5 – 1 mV 0.2 – 200 Hz Eye

BMIS 471 Biomedical Electronic Instruments - 1