final documentation

CHAPTER-1

INTRODUCTION

1.1 ANATOMY OF SKIN

The skin is an ever-changing organ that contains many specialized cells

and structure. It is also very involved in maintaining the proper temperature for

the body to function well. It gathers sensory information from the environment,

and plays an active role in the immune system protecting us from disease.

Understanding how the skin can function in these many ways starts with

understanding the structure of the three layers of skin - the epidermis, dermis,

and subcutaneous tissue.

1.1.1 Epidermis

Epidermis, "epi" coming from the Greek meaning "over" or "upon", is

the outermost layer of the skin. It forms the waterproof, protective wrap over

the body's surface and is made up of stratified squamous epithelium with an

underlying basal lamina. The epidermis contains no blood vessels, and cells in

the deepest layers are nourished by diffusion from blood capillaries extending to

the upper layers of the dermis. The main types of cells which make up the

epidermis are Merkel cells, keratinocytes with melanocytes. Sometimes

Langerhans cells are also present. The epidermis can be further subdivided into

the following strata (beginning with the outermost layer): corneum, lucidum

(only in palms of hands and bottoms of feet), granulosum, spinosum, basale.

Cells are formed through mitosis at the basal layer. The daughter cells (see cell

division) move up the strata changing shape and composition as they die due to

isolation from their blood source. The cytoplasm is released and the protein

keratin is inserted. They eventually reach the corneum and slough off 1

(desquamation). This process is called keratinization and takes place within

about 27 days. This keratinized layer of skin is responsible for keeping water in

the body and keeping other harmful chemicals and pathogens out, making skin a

natural barrier to infection. The epidermis helps the skin to regulate body

temperature. The thickness of the epidermis varies in different types of skin. It

is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles

at 1.5 mm.

The epidermis contains 5 layers. From bottom to top the layers are named:

stratum basale

stratum spinosum

stratum granulosum

stratum licidum

stratum corneum

The bottom layer, the stratum basale, has cells that are shaped like columns. In

this layer the cells divide and push already formed cells into higher layers. As

the cells move into the higher layers, they flatten and eventually die.

The top layer of the epidermis, the stratum corneum, is made of dead, flat skin

cells that shed about every 2 weeks.

Specialized Epidermal Cells

There are three types of specialized cells in the epidermis.

The melanocyte produces pigment (melanin).

The Langerhans' cell is the frontline defence of the immune system in the skin.

The Merkel's cell's function is not clearly known.

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1.1.2 Dermis

The dermis is the layer of skin beneath the epidermis that consists of

connective tissue and cushions the body from stress and strain. The dermis is

tightly connected to the epidermis by a basement membrane. It also harbours

many Mechanoreceptors (nerve endings) that provide the sense of touch and

heat. It contains the hair follicles, sweat glands, sebaceous glands, apocrine

glands, lymphatic vessels and blood vessels. The blood vessels in the dermis

provide nourishment and waste removal from its own cells as well as from the

Stratum basale of the epidermis.The dermis are structurally divided into two

areas: a superficial area adjacent to the epidermis, called the papillary region,

and a deep thicker area known as the reticular region.

The dermis also varies in thickness depending on the location of the skin. It is .3

mm on the eyelid and 3.0 mm on the back. The dermis is composed of three

types of tissue that are present throughout - not in layers. The types of tissue

are:

Collagen.

Elastic tissue.

Reticular fibers.

The two layers of the dermis are the papillary and reticular layers.

The upper, papillary layer contains a thin arrangement of collagen

fibers.

The lower, reticular layer is thicker and made of thick collagen fibers

that are arranged parallel to the surface of the skin.

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Papillary region

The papillary region is composed of loose areolar connective tissue.

This is named for its finger like projections called papillae, which extend

toward the epidermis. The papillae provide the dermis with a "bumpy" surface

that interdigitates with the epidermis, strengthening the connection between the

two layers of skin.

Reticular region

The reticular region lies deep in the papillary region and is usually much

thicker. It is composed of dense irregular connective tissue, and receives its

name from the dense concentration of collagenous, elastic, and reticular fibres

that weave throughout it. These protein fibres give the dermis its properties of

strength, extensibility, and elasticity. Also located within the reticular region are

the roots of the hair, sebaceous glands, sweat glands, receptors, nails, and blood

vessels.

Specialized Dermal Cells

Dermis contains many specialized cells and structures.

The hair follicles are situated here with the erector pili muscle that

attaches to each follicle.

Sebaceous (oil) glands and apocrine (scent) glands are associated with

the follicle.

This layer also contains eccrine (sweat) glands, but they are not

associated with hair follicles.

Blood vessels and nerves course through this layer. The nerves transmit

sensations of pain, itch, and temperature.

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There are also specialized nerve cells called Meissner's and Vater-Pacini

corpuscles that transmit the sensations of touch and pressure.

1.1.3 Hypodermis

The hypodermis is not part of the skin, and lies below the dermis. Its

purpose is to attach the skin to underlying bone and muscle as well as supplying

it with blood vessels and nerves. It consists of loose connective tissue and

elastin. The main cell types are fibroblasts, macrophages and adipocytes (the

hypodermis contains 50% of body fat). Fat serves as padding and insulation for

the body. Another name for the hypodermis is the subcutaneous tissue.

Microorganisms like Staphylococcus epidermidis colonize the skin surface. The

density of skin flora depends on region of the skin. The disinfected skin surface

gets recolonized from bacteria residing in the deeper areas of the hair follicle,

gut and urogenital openings.

Fig. 1.1 Anatomy of skin

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1.2 THE BIOLOGY OF WOUND HEALING

With the wounding of healthy tissue, a predictable progression of

physiologic events unfolds. This progression can be divided into three phases.

Inflammation

Proliferation and

Maturation.

Each phase is characterized by the sequential elaboration of distinctive

cytokines by specific cells.

1.2.1Inflammatory phase

The inflammatory phase simultaneously launches hemostatic

mechanisms and pathways that create the clinically recognizable cardinal signs

of inflammation: rubor (redness), calor (warmth), tumor (swelling), dolor

(pain), and functio laesa (loss of function).

Injury to vascular tissue initiates the extrinsic coagulation cascade by

releasing intracellular calcium. The resulting fibrin plug achieves hemostasis

aided by reflex vasoconstriction. This plug acts as a lattice for the aggregation

of platelets, the most common and “signature” cell type of the early

inflammatory phase.

After initial vasoconstriction, the classic signs of inflammation manifest from

increased vascular permeability. Redness results from vasodilation, mediated by

prostacyclin (PGI2), prostaglandin A (PGA), prostaglandin D (PGD), and

prostaglandin E (PGE). Swelling and warmth develop as vascular endothelial

gaps enlarge, allowing the egress of plasma protein and fluid into the interstitial

space. These changes are potentiated by PGE2 and prostaglandin and allow the

ingress of inflammatory cells into the area of injury, including cells that

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elaborate. Dolor is sensed as PGI2, PGE, and PGE2 act on peripheral

nociceptors.

In the second stage of the inflammatory phase, leukocytes supplant

platelets as the dominant cell type, attracted by chemotaxis. White blood cells

(WBCs) are the predominant cells for the first 3 days after wounding; their

numbers peak at approximately 48 hours. Polymorphonucleocytes (PMNs) are

the first to begin bactericidal activities using inflammatory mediators and

oxygen free radical metabolites. However, normal wound healing can occur

without PMNs.

As PMN leukocytes begin to wane after 24-36 hours, circulating

monocytes enter the wound and mature into tissue macrophages. These cells

deride the wound on the microscopic level and produce a wide variety of

important substances, such as basic fibroblast growth factor (bFGF). bFGF is a

chemotactic and mitogenic factor for fibroblasts and endothelial cells. Unlike

PMNs, macrophage depletion severely impairs wound healing, as debridement,

fibroblast proliferation, and angiogenesis all diminish.

The macrophage-derived growth factors are now at optimal levels,

strongly influencing the influx of fibroblasts and then keratinocytes and

endothelial cells into the wound. As mononuclear cells continue to replace

WBCs and macrophages, the proliferative phase begins.

1.2.2 Proliferative phase

Two to three days after wounding, fibroblasts migrate inward from

wound margins over the fibrinous matrix established during the inflammatory

phase. During the first week, fibroblasts begin producing glycosaminoglycans

and proteoglycans, the ground substance for granulation tissue, as well as

collagen, in response to macrophage-synthesized bFGF.

Fibroblasts soon become the dominant cell type, peaking at 1-2 weeks. They

generate not only collagen molecules but also cytokines such as PDGF, bFGF,

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keratinocyte growth factor, and insulin like growth factor-1. Fibroblasts also

assemble collagen molecules into fibers, which are cross-linked and organized

into bundles. Collagen is the major component of acute wound connective

tissue, with net production continuing for the next 6 weeks. The increasing

content of wound collagen correlates with increasing tensile strength.

Keratinocytes and endothelial cells also proliferate during this time,

eventually producing autocrine growth factors that maintain their growth.

Endothelial expansion contributes to angiogenesis, as intact vessels generate

buds in granulation tissue. Neovascularisation facilitates growth of the

advancing line of fibroblasts into the wound, providing them with necessary

nutrients and cytokines.

Degradation of the fibrin clot and provisional matrix is accompanied by

the deposition of granulation tissue (ground substance, collagen, capillaries),

which continues until the wound is covered. Decreasing hyaluronic acid (in

ground substance) levels and increasing chondroitin sulphate levels slow

fibroblast migration and proliferation while inducing fibroblast differentiation,

transitioning to the maturation phase of wound healing.

1.2.3 Maturation phase

For the first 6 weeks, new collagen production dominates the wound

healing process, deposited randomly in acute wound granulation tissue. As the

wound matures, collagen is remodelled into a more organized structure with

increased tensile strength. Gradually, type I collagen replaces type III until the

normal skin ratio is achieved. As the remodelling continues, the matrix

metalloproteinase collagenolysis achieves a steady state with collagen synthesis.

Superficial to this activity, epithelial cells continue to migrate inward

from the wound edge until the defect is covered. At this point, contact inhibition

induces transformation of fibroblasts into myofibroblasts, which contain

contractile actin fibers. Wound contraction follows, replacing injured tissue

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volume with new tissue, although the exact role of the myofibroblast has not

been fully elucidated.

1.3 COMMON CHRONIC WOUNDS

Common chronic skin and soft tissue wounds include the diabetic foot

ulcer, the pressure ulcer, and the venous stasis ulcer.

1.3.1 Diabetic foot ulcers

Diabetic ulcers are responsible for most foot and leg amputations.

Pathogenesis is due to neuropathic impairment of musculoskeletal balance as

well as immune compromise from leukocyte dysfunction and peripheral

vascular disease, complicating these wounds with infection. Standard of care

includes off-loading, attentive debridement, maintenance of a moist wound

environment, and, when cellulitis is present, systemic antibiotics. Chronic

wounds have decreased levels of growth factors, and topical platelet-derived

growth factor (PDGF). Tissue growth factor beta (TGF- ß), and platelet-derived

wound healing factor have been demonstrated to speed the healing of diabetic

ulcers.

1.3.2 Pressure ulcers

Pressure ulcers result from ischemia due to prolonged pressure over a

bony prominence. They typically occur in paralyzed or unconscious patients

who unable to either sense or respond to the need for periodic repositioning.

Preventive measures include identification of high-risk patients, frequent

assessment, scheduled repositioning, pressure-relief bedding, moisture barriers,

and adequate nutritional status. Treatment consists of pressure relief, enzymatic

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and surgical debridement, and maintenance of a clean, moist wound

environment.

1.3.3 Venous stasis ulcers

Venous stasis ulcers result from hypoxia in the areas of venous

congestion in the lower extremity. Possibly, the thick perivascular fibrin cuffs

impede oxygen diffusion into the surrounding tissues. Alternately,

macromolecules leaking into the perivascular tissue trap may growth factors

needed for the maintenance of skin integrity. A third potential cause may be

leukocytes migrating through capillaries more slowly than usual, even

occluding them, becoming activated, and damaging the vascular endothelium.

Compression hose or boots, debridement, and maintenance of a clean,

moist wound environment are the mainstays of therapy. Split-thickness skin

grafts and bioengineered skin equivalent (Apligraf, Organogenesis) have both

been shown to be effective, providing matrices, migration pathways, growth

factors, and living dermal and epidermal cells to the wound. In addition to

compressive bandaging, surgery to correct venous reflux does not appear to

improve ulcer healing, though it may reduce the recurrence of problem wounds.

1.4 SKIN IMPEDANCE

1.4.1 Resistance

All substances have resistance to the flow of an electric direct current

(DC). Resistance refers to the obstacle of direct current. Impedance refers to the

obstacle of alternating current. Ohm’s law states that the resistance of a

substance is proportional to the voltage drop of an applied current as it passes

through a resistive substance, or

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Resistance= Applied Voltage (volts) / Current (Amps)

An ohm is a unit of electrical resistance equal to the resistance of a circuit in

which an electromotive force of one volt maintains a current of one ampere. In

the body, highly conductive lean tissues contain large amounts of water and

conducting electrolytes, and represent a low resistance electrical pathway. Fat

and bone, on the other hand, are poor conductors.

1.4.2 Reactance

Reactance, also known as capacitive reactance when describing

biological tissues, is the opposition to the instantaneous flow of electric current

caused by capacitance or a high resistance electrical pathway with low amounts

of fluid and conducting electrolytes. In the healthy living body, the cell

membrane consists of a layer of non-conductive lipid material sandwiched

between two layers of conductive protein molecules. The structure of cell

membranes makes them capacitive reactive elements which behave as

capacitors when exposed to an alternating current.

Skin impedance is a term used to describe the response of a living

organism to an externally applied electric current. It is a measure of the

opposition to the flow of electric current through the tissues. The body offers

two types of R to an electrical current: capacitative R (reactance), and resistive

R (simply called resistance). The capacitance arises from cell membranes, and

the R from extra- and intracellular fluid. Impedance is the term used to describe

the combination of the two. Several electrical circuits have been used to

describe the behaviour of biological tissues in vivo. One of them involves

arranging R and capacitance in series, another in parallel, whilst others are more

complex. In order to analyze the measured impedance, a simple equivalent

circuit model is often used.

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Fig.1.2 Equivalent circuit of wound impedance

The outer, dry epidermis shows capacitive behaviour at high

frequencies. At low frequencies, however, only resistive properties can be

measured for this layer. This has lead to the modelling of the epidermis by a

resistor Rp in parallel with a capacitor C. Underneath the epidermis lie the

moister dermal layers. Currents can flow through these layers relatively

unimpeded and they are therefore represented by a small resistance Rs in series

with the aforementioned parallel circuit. It has been observed, however, that the

phase angle of the capacitive element of the circuit, although constant over a

considerable range of frequencies, is not the expected 90 of an ideal capacitor.

An alternating current is an oscillating current which passes through a

conductor alternately in one direction then in the opposite direction, a certain

number of times per second. An alternating current is used for measuring skin

impedance because a biological tissue is an ionic conductor: it is known that

electrical conduction in a material occurs through charge carriers, which may be

electrons, such as is the case for metals; or free ions in suspension in solutions,

as is the case for biological tissues. If a direct current is passed through an

ionized solution, the well-known phenomenon of polarization occurs, i.e. very

rapidly at the level of each electrode a double layer of ions is deposited which

acts as an insulator and prevents the current from passing. Direct current travels

in only one direction. DC cannot be used to measure the resistance of the human

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body. DC current causes ions to build up eventually causing polarization. This

can cause heating in tissue if one is not careful.

When one studies the impedance Z of a biological conductor it may be

observed that it varies according to the frequency of the measurement current.

The higher the frequency the more easily the current passes and consequently,

the lower the impedance. Higher the frequency lesser will be the resistance. At

about 1MHz (1 million cycles per second or hertz) there is no more resistance in

the biological tissue of the body .Very low frequencies only travel through the

connective tissue of the body. At about 10,000 hertz frequencies begin to

penetrate the outside layers of the cell.

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CHAPTER 2

CURRENT WOUND ASSESSMENT

2.1 EXISTING METHODS

There are many techniques that are being used to monitor the progress

of wound healing progress. It is critically important to accurately and precisely

determine and document the progress (or otherwise) of its healing in order to

chose/develop the most effective treatment. Most of these techniques require

removal of dressing.

These methods involve:

2.1.1 Tracing method

This method involves tracing the wound on transparency film with a

fine-tipped pen, and analyzing the traced area manually by counting the number

of squares.

2.1.2 Digitizer

Digitally by means of a planimeter or digitizer or taking a scaled

photographs of the wound.

Both these categories of techniques are found to be relatively reliable as

long as they are performed and analyzed by the same investigator. The

techniques fail, however, if a multicenter trial is performed as it is not always

possible to use the same investigator, and hence, ensure the same systematic

errors.

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Although direct-wound tracing is an inexpensive and convenient method,

albeit time-consuming; it is invasive as the transparencies have to make contact

with the wounds. This has the real potential to further disrupt the wound healing

process (ironically, dressing removal in itself can interfere with healing), and

thus, lead to contamination, the pathogens in the wound fluid spreading to

clinicians and other patients.

2.1.3 Visitrack system

A further example of a wound tracing technique is Smith and Nephew’s

Visitrack system; a clipboard like device used to trace the wound as shown in

fig. 2.1. Initially, a layered grid is applied to the wound. The clinician then

traces the wound, removes the top layer of the grid and attaches it to the

electrical clipboard. He then has to trace the wound again to enable the digital

analysis. Any error in tracing will be multiplied by the repetition of the process.

Fig.2.1 Visitrack System from Smith and Nephew.

The noncontact photographic technique (planimetry) eliminates the

increased risk of contamination or wound interference associated with direct-

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contact methods (dressing removal is still required), however, the ease of use is

offset by costly, bulky equipment, and intensive training requirements. The

digital image must be of a high resolution, however, even with this, it is still

very difficult.

2.1.4 Stereophotogrammetry

To overcome the limitations of the photographic (and other) methods,

the latest approach is to use stereophotogrammetry, a stereo camera combined

with a computer system generates a 3-D characterization of the wound. Once

again expensive, bulky equipment and intensive training are required, making it

a useful tool for clinical trials, but not practicable for routine care.

2.1.5 PDA powered laser digitizer

A recently launched technique is the use of a personal digital assistant

(PDA)-powered laser digitizer, as shown in fig.2.2. Images can be analyzed and

documented, and then, transferred to an electronic patient file. Ease-of-use is

greatly increased in this case.

Fig.2.2 PDA powered laser digitizer

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2.2 ADVANTAGES AND DISADVANTAGES OF THESE

METHODS

2.2.1 Advantages

1. Inexpensive

2. Convenient to Use

2.2.2 Disadvantages

Invasive and makes contacts with the wound

Requires opening of the bandage

May lead to infections due to exposure

Disrupts wound healing process

Time Consuming

To date no technique is available that can be readily performed by the

patient or his family that would enable them to take a more active role in wound

management. The professional clinician is required to identify the progress of

wound healing and to decide on any further treatment based on the wound

characterization. No technique is available that could perform/enable this

characterization without the removal of the wound dressing, which can lead to

disturbance of the wound healing processes and to increased risk of

contamination.

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CHAPTER 3

BLOCK DIAGRAM

3.1 INTRODUCTION

The proposed method of monitoring wound healing is based on the

measurement of the tissue impedance and temperature; hence could enable the

investigator to assess the wound healing progress without removing the

dressing, and thus, avoiding interfering with wound healing. It is targeted at the

monitoring of chronic wounds, but could also be utilized in the study or

diagnosis of acute wounds or burns. The basic principle behind this proposed

model is that intact skin has high impedance, whereas an open wound has very

low impedance, the latter largely due to the resistance of the underlying dermis.

Similarly the temperature of the areas around the wound will be higher than the

normal skin temperature due to the increased blood flow to the wounded area.

So this model measures the normal skin impedance, the normal skin

temperature, the skin impedance and the temperature in the wounded tissues.

Then the normal values of temperature and skin impedance are compared with

the values that are measured for the wound and the wound healing progress is

assessed.

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BLOCK DIAGRAM

Fig.3.1.Block Diagram

19

OSCILLATOR

(100 Hz)AMPLIFIER

AMPLIFIER

PIC 16F877

ADCDISPLAY

3.2 DESCRIPTION

This project makes use of five skin electrodes and two temperature

sensors. Two skin electrodes are used as transmitters, two are used as receivers

and the remaining one electrode is used for grounding. A set of transmitter and

receiving electrodes are placed on the normal skin. This is used for measuring

the normal skin impedance. A temperature sensor is also used on the normal

skin to measure the normal skin temperature. A similar set up of electrodes are

used to measure the impedance of the skin with the wound. The transmitter and

the receiving electrodes are placed on either side of the bandage .The

temperature sensor is placed close to the bandage around the bandage. The

oscillator circuit generates a frequency of 100 Hz. This is then given to both the

transmitting electrodes. The signal passes through the normal skin and the

wound. The signals are captured by the receiver electrodes. The signals passing

through the wound undergoes changes in frequency. These signals are then

amplified, filtered and given to the microcontroller. At the same time the

temperature of normal skin and wounded skin will be sensed by temperature

sensor and it is also given to the controller as shown in fig.3.1.The results are

displayed on the LCD screen.

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CHAPTER 4

HARDWARE DESCRIPTION

The hardware part of this project includes the five skin electrodes, two

temperature sensors, power supply circuit, oscillator circuit, the signal

processing circuitary, microcontroller, the interfacing unit and the display unit.

The oscillator circuit generates a signal of frequency 100 Hz. The skin

electrodes are used for transmission and reception of signals from the skin and

the temperature sensors are used for measuring skin temperature. The signal

processing unit performs the signal conditioning and provides the patient

isolation unit to ensure patient safety. The values are displayed on the LCD

display or the prototype can be interfaced to a computer where the values are

displayed.

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4.1 CIRCUIT DESCRIPTION

The signals picked up by the receiver electrodes are fed to the

amplifiers. The signals picked up from the body are very weak in the order of a

few mill volts. These signals are to be converted in the order of volts for the

proper analysis. Amplifiers are used for this purpose. IC TL072 and IC TL074

are used amplifiers in this circuit. This amplified signal contains the line

frequency, high frequency and low frequency noise signals. So the signal is fed

to filter section. The filter section consists of high pass filter and low pass filter

which is used to remove the high frequency and low frequency noise signal.

The cut off frequency of the high pass filter is tuned at 10Hz and that of low

pass filter is tuned to pass frequencies below 1 KHz. Then the filtered signals

are fed to a clamper circuit to shift the dc level of the signal to a value required

to bias the isolation circuit. The filtered signals are fed to the patient isolation

circuit which includes a pulse width modulator, optocoupler and demodulator.

The isolation is necessary to isolate the human body and monitoring equipment,

to ensure patient safety. In this section the incoming signals are converted to

pulses by the PWM. The width of the pulses depends on the amplitude of the

incoming signal .The carrier signal used for modulation has a frequency of 2

KHZ. These pulses are then sent to the optocoupler which includes a LED and a

phototransistor. For each pulse that has been received the LED emits light

which falls on the phototransistor. For each light signal that falls on the

phototransistor it produces pulses which are sent to pulse demodulation unit

where the carrier signal is removed and the original signal is retrieved again.

Then the wave is fed to notch filter section in order to remove the line

frequency noise signal. A notch filter is a band-stop filter with a narrow stop

band. Here the notch filter is constructed by the operational amplifier TL074.

Finally noise free signal is given to amplifier. Then the amplified signal is given

to PIC microcontroller.

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4.2ELECTRODES

The skin electrodes act as both transmitter and receiver. The frequencies

generated by the oscillator circuit are transmitted to the knee through the

transmitting electrodes and the corresponding signals are received by the

receiver electrodes for both normal skin and the wound. These signals are

amplified, filtered and fed to the microcontroller.

The electrodes chosen for this project are disc electrodes made up of

conducting materials like copper. These electrodes provide good contact with

skin to enable the proper transmission and reception of signals.

4.3 TEMPERATURE SENSOR

Fig.4.2 Thermistor Circuit

A thermistor is a type of resistor used to measure temperature changes,

relying on the change in its resistance with changing temperature. In this project

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we are using negative temperature coefficient thermistors (NTC thermistors)

(fig.4.2).These are sensors whose output voltage is linearly proportional to the

Celsius temperature. It does not require any external calibration or trimming. It

has low output impedance; linear output and precise inherent calibration make

interfacing to readout or control circuitry easy. It can be used with single power

supply.

Features:

• Low cost solid state sensor

• Standard resistance tolerances down to ±2%

• High sensitivity to changes in temperature

• Excellent mechanical strength

• Wide operating temperature range: -50°C to 150°C

• Available in a wide range of material systems

4.4 POWER SUPPLY

The regulated power supply is made by converting the domestic ac

supply to dc supply. Power supply circuits are built using filters, rectifiers, and

then voltage regulators. Starting with an ac voltage, a steady dc voltage is

obtained by rectifying the ac voltage, then filtering to a dc level, and finally,

regulating to obtain a desired fixed dc voltage (fig.4.4).

4.4.1 Working principle

Transformer

The potential transformer will step down the power supply voltage (0-

230V) to (0-6V) level. Then the secondary of the potential transformer will be

connected to the bridge rectifier.

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Bridge Rectifier

When four diodes are connected as shown in figure, the circuit is called as

bridge rectifier. The input to the circuit is applied to the diagonally opposite

corners of the network, and the output is taken from the remaining two corners.

One advantage of a bridge rectifier over a conventional full-wave rectifier is

that with a given transformer the bridge rectifier produces a voltage output that

is nearly twice that of the conventional full-wave circuit. This resulting dc

voltage usually has some ripple or ac voltage variation. It is initially filtered by

a simple capacitor filter to produce a dc voltage.

Voltage Regulators

Voltage regulators comprise a class of widely used ICs. Regulator IC

units contain the circuitry for reference source, comparator amplifier, control

device, and overload protection all in a single IC. Although the internal

construction of the IC is somewhat different from that described for discrete

voltage regulator circuits, the external operation is much the same. IC units

provide regulation of either a fixed positive voltage, a fixed negative voltage,

or an adjustably set voltage.

A power supply can be built using a transformer connected to the ac

supply line to step the ac voltage to desired amplitude, then rectifying that ac

voltage, filtering with a capacitor and RC filter, if desired, and finally regulating

the dc voltage using an IC regulator. The regulators can be selected for

operation with load currents from hundreds of milli amperes to tens of amperes,

corresponding to power ratings from milli watts to tens of watts.

Three-terminal voltage regulators:

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Fig. 4.3 shows the basic connection of a three-terminal voltage regulator

IC to a load. The fixed voltage regulator has an unregulated dc input voltage,

Vi, applied to one input terminal, a regulated output dc voltage, Vo, from a

second terminal, with the third terminal connected to ground. For a selected

regulator, IC device specifications list a voltage range over which the input

voltage can vary to maintain a regulated output voltage over a range of load

current. The specifications also list the amount of output voltage change

resulting from a change in load current (load regulation) or in input voltage (line

regulation).

Fixed Positive Voltage Regulators:

Fig. 4.3 Voltage regulator

The series 78 regulators provide fixed regulated voltages from 5 to 24 V. An

unregulated input voltage Vi is filtered by capacitor C1 and connected to the

IC’s IN terminal. The IC’s OUT terminal provides a regulated + 12V which is

filtered by capacitor C2 (mostly for any high-frequency noise). The third IC

terminal is connected to ground (GND). While the input voltage may vary over

some permissible voltage range, and the output load may vary over some

acceptable range, the output voltage remains constant within specified voltage

variation limits.

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4.1.2 CIRCUIT DIAGRAM

Fig 4.4 Power Supply Circuit

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4.5 OSCILLATOR CIRCUIT

Fig. 4.5 Oscillator circuit

CIRCUIT DESCRIPTION

The oscillator circuit is made up of IC 4046 which generates a signal of

desired frequency depending upon the RC value as shown in fig 4.5. Here we

have a 10K variable resistor which is connected in series with another resistor.

When the value of this variable resistor is varied, the total resistance of the

resistors which are connected in series, changes. This changes the frequency of

the signal that is generated by the IC 4046.

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IC 4046

The IC 4046 is a CMOS Micro power Phase locked loop IC which

consists of a low power, voltage controlled oscillator and two different phase

comparators having a common signal-input amplifier and a common

comparator input. A 5.2 V zener diode is provided for supply regulation if

necessary.

Features:

Very low power consumption

Wide operating frequency range

High voltage controlled oscillator linearity

Low frequency drift

Zener diode to assist supply regulation

Standardised symmetrical output characteristics

4.6 TL-071 –JFET OP AMP

The instrumentation amplifier is constructed by the TL 071 operational

amplifier. The TL071 are high speed J-FET input dual operational amplifier

incorporating well matched, high voltage J-FET and bipolar transistors in a

monolithic integrated circuit (fig.4.5). The devices feature high slew rates, low

input bias and offset current and low offset voltage temperature coefficient.

FEATURES OF TL-071

Low input bias and offset current

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Low noise

Output short-circuit protection

High input impedance JFET input stage

Wide common-mode and differential voltage range

Low harmonic distortion :

Internal frequency compensation

Latch up free operation

High slew rate : 16v/ms

Fig.4.5.TL-071 IC

4.7 TL 074-JFET OP AMP

The TL074, TL074A and TL074B are high speed J–FET input quad

operational amplifiers incorporating well matched, high voltage J–FET and

bipolar transistors in a monolithic integrated circuit (fig.4.6). The devices

feature high slew rates, low input bias and offset currents, and low offset

voltage temperature coefficient.

FEATURES OF TL-074

Low input bias and offset current

Low noise 30

Output short-circuit protection high input impedance JFET input stage

Low harmonic distortion

Low power consumption wide common-mode and differential voltage

range

Internal frequency compensation

Latch up free operation

High slew rate : 13v/ms

Fig. 4.6 TL-074 IC

4.8 PIC MICROCONTROLLER

Microcontroller is a general purpose device, which integrates a number

of the components of a microprocessor system on to single chip. It has inbuilt

CPU, memory and peripherals to make it as a mini computer.

The microcontroller that has been used for this project is from PIC

series. PIC microcontroller is the first RISC based microcontroller fabricated in

CMOS (complementary metal oxide semiconductor) that uses separate bus for

instruction and data allowing simultaneous access of program and data memory.

The main advantage of CMOS and RISC combination is low power

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consumption resulting in a very small chip size with a small pin count as in

fig.4.8. The main advantage of CMOS is that it has immunity to noise than

other fabrication techniques.

PIC (16F877):

Fig.4.7 Pin Diagram of PIC16F877

Various microcontrollers offer different kinds of memories. EEPROM,

EPROM, FLASH etc. are some of the memories of which FLASH is the most

recently developed. Technology that is used in PIC16F877 is flash technology,

so that data is retained even when the power is switched off. Easy Programming

and Erasing are other features of PIC 16F877.

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4.7.1 Special features of PIC microcontroller:

• High-performance RISC CPU

• Only 35 single word instructions to learn

• All single cycle instructions except for program branches which are two

cycle

• Operating speed: DC - 20 MHz clock input

DC - 200 ns instruction cycle

• Up to 8K x 14 words of Flash Program Memory,

Up to 368 x 8 bytes of Data Memory (RAM)

Up to 256 x 8 bytes of EEPROM data memory

• Pin out compatible to the PIC16C73/74/76/77

• Interrupt capability (up to 14 internal/external)

• Eight level deep hardware stack

• Direct, indirect, and relative addressing modes

• Power-on Reset (POR)

• Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)

• Watchdog Timer (WDT) with its own on-chip RC Oscillator for reliable

operation

• Programmable code-protection

• Power saving SLEEP mode

• Selectable oscillator options

• Low-power, high-speed CMOS EPROM/EEPROM technology

• Only single 5V source needed for programming capability

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• In-Circuit Debugging via two pins

• Processor read/write access to program memory

• Wide operating voltage range: 2.5V to 5.5V

• High Sink/Source Current: 25 mA

• Commercial and Industrial temperature ranges

• Low-power consumption

4.9 INTERFACING

RS-232 is a standard for serial binary data interconnection between a

DTE (Data terminal equipment) and a DCE (Data Circuit-terminating

Equipment). It is commonly used in computer serial ports. Details of character

format and transmission bit rate are controlled by the serial port hardware, often

a single integrated circuit called a UART that converts data from parallel to

serial form. A typical serial port includes specialized driver and receiver

integrated circuits to convert between internal logic levels and RS-232

compatible signal levels as given in fig.4.8

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Fig.4.8 Logic Diagram and Function Tables

CIRCUIT WORKING DESCRIPTION:

In this circuit the MAX 232 IC used as level logic converter. The

MAX232 is a dual driver/receiver that includes a capacitive voltage generator to

supply EIA 232 voltage levels from a single 5V supply. Each receiver converts

EIA-232 to 5V TTL/CMOS levels. Each driver converts TLL/CMOS input

levels into EIA-232 levels.

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Fig. 4.9 RS-232 Interfacing

In this circuit the microcontroller transmitter pin is connected in the

MAX232 T2IN pin which converts input 5V TTL/CMOS level to RS232 level.

Then T2OUT pin is connected to reviver pin of 9 pin D type serial connector

which is directly connected to PC as shown in fig.4.9.

In PC the transmitting data is given to R2IN of MAX232 through

transmitting pin of 9 pin D type connector which converts the RS232 level to 5v

TTL/CMOS level. The R2OUT pin is connected to receiver pin of the

microcontroller. Likewise the data is transmitted and received between the

microcontroller and PC or other device vice versa.

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4.10 DISPLAY

There are two main displays used in this project to display the monitored

parameters.

A 20×4 LCD display which is mounted on the prototype

A display of the monitored parameters in the PC along with a graph to

show the wound healing progress for a patient. This is developed using

LabVIEW software.

37

CHAPTER 5

LabVIEW

LabVIEW (short for Laboratory Virtual Instrumentation Engineering

Workbench) is a platform and development environment for a visual

programming language from National Instruments. The purpose of such

programming is automating the usage of processing and measuring equipment

in any laboratory setup. LabVIEW is commonly used for data

acquisition, instrument control, and industrial automation on a variety of

platforms including Microsoft Windows, various versions of UNIX, Linux,

and Mac OS X. The latest version of LabVIEW is version LabVIEW 2010,

released in August 2010. LabVIEW is a graphical programming environment

used by millions of engineers and scientists to develop sophisticated

measurement, test, and control systems using intuitive graphical icons and wires

that resemble a flowchart. It offers unrivalled integration with thousands of

hardware devices and provides hundreds of built-in libraries for advanced

analysis and data visualization–all for creating virtual instrumentation. The

LabVIEW platform is scalable across multiple targets and OSs, and, since its

introduction in 1986, it has become an industry leader.

Graphical programming

LabVIEW ties the creation of user interfaces (called front panels) into

the development cycle. LabVIEW programs/subroutines are called virtual

instruments (VIs). Each VI has three components: a block diagram, a front

panel and a connector panel. The last is used to represent the VI in the block

diagrams of other, calling VIs. Controls and indicators on the front panel allow

an operator to input data into or extract data from a running virtual instrument.

However, the front panel can also serve as a programmatic interface. Thus a

38

virtual instrument can either be run as a program, with the front panel serving as

a user interface, or, when dropped as a node onto the block diagram, the front

panel defines the inputs and outputs for the given node through the connector

pane. This implies each VI can be easily tested before being embedded as a

subroutine into a larger program. The graphical approach also allows non-

programmers to build programs by dragging and dropping virtual

representations of lab equipment with which they are already familiar. The

LabVIEW programming environment, with the included examples and the

documentation, makes it simple to create small applications. For complex

algorithms or large-scale code, it is important that the programmer possess an

extensive knowledge of the special LabVIEW syntax and the topology of its

memory management. The most advanced LabVIEW development systems

offer the possibility of building stand-alone applications.

39

5.1 FRONT PANEL

Fig. 5.1 Front Panel

40

5.2 BLOCK DIAGRAM

Fig. 5.2 Block Diagram

41

CHAPTER 6

CASE STUDY

Skin impedance is a term used to describe the response of a living

organism to an externally applied electric current. It is a measure of the

opposition to the flow of electric current through the tissues. When one studies

the impedance of a biological conductor it may be observed that it varies

according to the frequency of the measurement current. The higher the

frequency the more easily the current passes and consequently, the lower the

impedance. The higher the applied frequency, the lesser will be the impedance.

Abrasion of skin causes reduction in skin impedance. There will be an increased

cellular activity in the wounded tissues which leads to an increased blood flow

to the wounded tissues. Hence the temperature in the tissues with wound will be

higher than the normal skin temperature.

In this proposed model of wound monitoring, the measured parameters

are normal skin impedance, skin impedance of the tissue with wound, normal

skin temperature and temperature of the wounded tissue. For these

measurements we make use of five skin electrodes and two temperature sensors.

Among the five skin electrodes, two electrodes act as transmitters and two

electrodes act as receivers and one electrode acts as ground electrode. A

transmitter and a receiver are placed on the normal skin to measure the normal

skin impedance. A thermistor is also placed on the normal skin to measure the

normal skin temperature. We have a similar set up of electrodes is placed on the

skin with wound. The transmitter and receiver electrodes are placed on either

side of the bandage and a thermistor is placed very close to the bandage. The

parameters are measured .The values obtained for normal skin and the skin with

wound are then compared .These values are used to assess the progress in

wound healing. These parameters are measured everyday or once in a few days

and the difference between the impedance values for normal skin and the skin

with wound are noted. It was observed that the impedance value for wound

42

increases as the wound healing progresses. The difference between the

impedance value for the wound and the normal skin is reduced as the wound

heals. Similarly temperature values also become nearly the same on the normal

skin and on the skin with wound as the wound heals.

CASE STUDY

The impedance measurements for four patients were conducted in

Ganga Hospital under the guidance of Dr.Ravindra Bharathi, Plastic Surgeon,

Ganga Hospital. The case study was conducted from the duration 12th March

2011 to 21th March 2011. The results of the case study proved that the device

can be successfully used for monitoring wound healing progress without the

need for opening the bandage.

43

CASE STUDY 1

Name : Mr. John Paul

Age : 26 yrs

Position of the wound : Right Foot

Parameters Day 1

Day 7

(After skin grafting)

Date 12-03-11 18-03-11

Impedance

(Ω)

Normal 154 116

Wound 82 98

Difference 72 18

Temperature

(0C)

Normal 35 34

Wound 36 35

Difference 1 1

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CASE STUDY 2

Name : Mr. Periasamy

Age : 50 yrs

Position of the wound : Left Ankle

Length of the wound : 9 cm

Parameters Day 1 Day 7 Day 10

Date 12-03-11 18-03-11 21-03-11

Impedance

(Ω)

Normal 123 123 177

Wound 66 110 166

Difference 57 13 11

Temperature

(0C)

Normal 35 34 35

Wound 34 35 35

Difference 1 1 0

45

CASE STUDY 3

Name : Mr. Kumaresan

Age : 32 yrs

Position of the wound : Left Thigh

Parameters Day 1 Day 7 After healing

Date 12-03-11 18-03-11 21-03-11

Impedance

(Ω)

Normal 163 110 148

Wound 103 93 137

Difference 63 17 11

Temperature

(0C)

Normal 33 32 34

Wound 34 33 34

Difference 1 1 0

46

CASE STUDY 4

Name : Mr. Chembaga Gounder

Age : 66

Position of the wound : Left Elbow

Parameters Day 1 Day 7 Day 10

Date 12-03-11 18-03-11 21-03-11

Impedance

(Ω)

Normal 100 151 103

Wound 66 121 83

Difference 34 30 20

Temperature

(0C)

Normal 34 33 33

Wound 36 35 33

Difference 2 2 0

47

The case study was conducted among four patients, Mr. John Paul,

Mr.Periasamy, Mr.Kumaresan and Mr.Chembaga Gounder. Mr. John Paul had a

wound on his right foot. On day 1, the difference in impedance values measured

on the normal skin and on the foot was about 72 Ω.On day 7, after skin grafting

the difference in impedance values reduced to 18Ω showing that the wound

healing is progressing after skin grafting. Mr Kumaresan had a deep wound on

his left thigh which initially showed a very low impedance value of 103

Ω,whereas the impedance value measured on normal skin was 163 Ω.On day

7,the difference between the two values reduced to 17Ω ,which further reduced

to11 Ω on day 10 which clearly indicated wound healing progress.

Mr.Periasamy had the wound on his left ankle, and initially the difference

between the measured impedance values for the normal skin and the wound was

57Ω which eventually reduced to13 Ω on day 7 and 11Ω on day 10.This again

shows that the impedance of the skin with the wound becomes closer to that of

the normal skin impedance as the wound heals. Mr.Chembaga Gounder had a

wound on his left elbow. In this case also, the difference between the normal

skin impedance and the impedance of the wound reduced to 20 Ω on day 10,

which had been 34 Ω on day 1 and 30 on day 7.In all the cases, the temperature

values showed a difference of 20C or 10C for the skin with wound and the

normal skin.

48

CHAPTER 7

RESULTS AND DISCUSSION

7.1 MERITS OF THE SYSTEM

The developed prototype has certain advantages over the conventional

methods used for assessing wound healing progress.

Few of these merits are enumerated as follows

Monitoring wound healing process without removing the dressing

This is the most important aspect of this system. Frequent removal of

dressings will cause the newly formed tissues to come off along with the

bandage. This exposes the wounds to external environments which may lead to

infections. These problems can be avoided by this method.

Use of Specialized bandages

This system permits the use of special kind of bandages that does not

require opening for at least 5 days. Such bandages are provided with special

kinds of fenestrated tubes for the necessary medication to reach the wound

area and for the removal of unwanted materials from the wound.

Protecting the wound from contamination

As this system does not require opening of bandage, the wound is

protected from contamination and thus from hospital acquired infections.

49

Less supervision by the clinician

The parameters can be measured by the patient himself with the help of

a nurse or a family member. The wound healing progress can be assessed by

them from the displayed values and the clinician can be informed later about

the condition of the wound.

Reduced hospitalization

The measurements can be done by patient at his home itself and thus

hospitalization is reduced.

Economic Criterion

This device will reduce hospitalization and thus the health care cost is

reduced. It is easy to fabricate and costs pretty low.

Simple and Reliable

The system is very easy to use. The wound healing can be monitored by

the patient himself or by his family members.

Portable

The system is portable because of its simple design criteria. It is

compact and can be carried anywhere.

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7.2 RESULTS

Our prototype aimed at monitoring of wound healing progress without

opening the dressing by measuring the skin impedance and temperature. It is

based on the principle that the skin with wound has lower skin impedance and a

higher temperature than the normal values of skin impedance and temperature.

The case study was conducted in four patients between the age group of 26 to

66. It proved that as the wound healing progresses the impedance value rises.

The difference between the impedance value for the wound and the normal skin

is reduced as the wound heals. Similarly temperature values also become nearly

the same on the normal skin and on the skin with wound as the wound heals.

51

PHTOGRAPHS OF THE PROJECT

PROTOTYPE

INTERNAL CIRCUITRY

52

PLACEMENT OF ELECTRODES ON NORMAL SKIN

DISPLAY

53

PLACEMENT OF ELECTRODES ON PATIENTS

Day 1

SKIN WITH WOUND NORMAL SKIN

DISPLAY

54

Day 10

SKIN WITH WOUND NORMAL SKIN

DISPLAY

55

CHAPTER 8

CONCLUSION AND FUTURE SCOPE

Our innovative idea of monitoring wound healing by measuring skin

impedance and temperature has been implemented and completed successfully.

This project titled ‘Remote Wound Monitoring of Chronic Ulcers’, aids the

diabetic patients, paraplegic patients and bedridden patients to self manage their

ulcers or wounds. The new device developed will enable clinicians to monitor

wound healing without disturbing, the wound-healing process. It has been

thoroughly evaluated and certified to be diagnostically good.

We are very happy that we were able to innovate in a rare area of

interest which is common in daily life but left unnoticed. Our idea has been

implemented successfully; however it requires certain modifications before it

can be commercially used.

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FUTURE SCOPE

The project can be made more efficient by implementing the following

ideas

Miniaturization of the device so that the device is more compact.

Incorporation of wireless Transmitter into the device.

This enables telemonitoring. Patient can be at home or in a remote place

and the recorded data can then be sent to the clinician.

This will enable patients and their families to optimally manage the

ulcers themselves under the guidance of a clinician. The cost of the healthcare

system is also reduced considerably .Such a monitoring system could be used to

improve the quality of care and give vital support and confidence to the patients

and their families.

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REFERENCES

1. Javier Rosell, Josep Colominas, Pere Riu, Ramon Pallas Areny, And John G.

Webster-Skin Impedance from 1 Hz to 1 MHz

2. Rudolph. J.Liedtke – Principles of Bio impedance Analysis.

3. Ursula .G. Kyle –Bio electrical Impedance Analysis, Principles and

Methods.

4. Rainer. J. Fink - Skin Impedance Matching System and Method for Skin

Electrode Interface.

5. Prof. Ritter – Variable Frequency Skin Impedance Monitor

6. www.wikipedia.com- Bioimpedance

7. www.dermatology.about.com – Anatomy of Skin

8. www.emedicine.medspace.com – Wound Healing

9. www.medicaledu.com – Phases of Wound Healing

10. www.analog.com – Trans dermal delivery.

11. www.copewithcytokines.com – wounding

12. www.datasheets.com

13. R. S. Khandpur – Handbook of Biomedical Instrumentation, Tata Mc-Graw-

Hill Publishing

14. S. Chand and Company Ltd – A text book of Applied Electronics

15. Rai Chaudry – Linear Integrated Circuits

16. S.Salivahanan, N. Suresh, A. Vallavaraj - Electronic Devices and Circuits

58