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Friday, 29 December 2017

Non Invasive Blood Pressure Measurement

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Non Invasive Blood Pressure Measurement

Invasive measurement refers to the measurement of BP by placing an intravascular cannula needle in the artery. As the name implies, in indirect measurements, the BP is measured indirectly and here we don’t require any direct contact with the artery. Hence it is called non-invasive measurement. The indirect or non-invasive measurements are simpler and quicker than invasive measurements.

1. Using Sphygmomanometer:

Normally physician measure blood pressure by a device called Sphygmomanometer. This comprises an inflatable cuff to restrict the blood flow and is placed around the upper arm attached to a mercury manometer. The mercury manometer measures the height of the mercury column through we can measure the blood pressure. The word sphygmomanometer comes from Greek works ‘sphygmos’ meaning pulse and ‘manometer’ meaning pressure meter.

Now digital sphygmomanometers are also used for the measurement. Here the process of making the measurement is done electronically and the display shows the result. The procedure for measuring the BP using sphygmomanometer is described below.

1. Firstly the cuff is wrapped around the patient’s upper arm at roughly same vertical height as heart. The cuff is placed over an artery. The physician then places his stethoscope over an artery downstream to the cuff.

2. Then the cuff is inflated so that the pressure inside the inflated bladder increases to a point greater than the expected systolic blood pressure. Since the cuff pressure is greater than the arterial pressure, an occlusion (interruption) to the blood flow occurs. So the blood flow in the vessels is shut off.

3. Then the physician slowly reduces the pressure in the cuff which causes the systolic pressure to increase. When the systolic pressure first exceeds the cuff pressure he can hear some crashing sounds in the stethoscope. These sounds are caused by the first jet of blood pushing through the occlusion when the occlusion is reduced. These sounds are called ‘Korotkoff’ sounds. By using the mercury manometer the physician can note the pressure at the onset of these sounds which will be the systolic pressure. As the physician still reduces the pressure on the cuff these sound disappear. The pressure corresponding to the disappearance of these sounds will be the diastolic pressure. In between systolic and diastolic pressures, we can hear some murmurs. Traditionally systolic pressure is the pressure at which the first Korotkoff sound is heard and diastolic pressure is the pressure at which Korotkoff sound is not audible.

Double Diastolic Pressure:

As the term means, in double diastolic pressure measurements, two diastolic pressures are take. First diastolic pressure is the pressure at which the Korotkoff sounds are very less audible. The second diastolic pressure is the pressure at which the Korotkoff sounds are not at all audible. Double diastolic pressure is indicated as (Systolic pressure/ 1st Diastolic pressure/2nd Diastolic pressure)mm Hg.
example for double diastolic pressure 120/80/77 mm Hg.

2. Ultrasonic blood pressure measurement:

Ultrasonic techniques can be used to measure arterial blood pressure indirectly with the same method as used for flow detection. Here piezoelectric crystals are placed between the patients arm and a blood pressure cuff.

The ultrasonic BP measurements are done with the help of Doppler Effect. The detailed working is explained below. The ultrasonic generator generates pulses and these are made to fall on the brachial artery. Due to the effect of pulses, the blood flow varies. This causes Doppler shift. The Doppler shift is measured by the ultrasonic circuits.

To measure Blood pressure, first the brachial artery is occluded and since there is no relative velocity between the transmitter and the receiver this time, the Doppler shift is zero. But as the Blood Pressure rises so that the arterial pressure is able to overcome the occlusion, a frequency shift is produced (200 – 500 Hz range). This is proportional to systolic pressure. Then as the arterial pressure reaches the diastolic pressure, the frequency shift due to Doppler effect is around 25 – 100 Hz. So by comparing the frequency shift caused due to each heart beat the Blood pressure can be measured by comparing the frequency shifts obtained  each time with the standard reference values. pt>

Wednesday, 20 December 2017

Systolic Pressure and Diastolic Pressure

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Blood pressure (BP) is the pressure exerted by the circulating blood on the walls of blood vessels. For each heart beat the blood pressure varies between systolic and diastolic pressures.

Systolic Pressure and Diastolic Pressure: Systolic pressure is the peak pressure in the arteries, when the ventricles are contracting. It occurs towards the end of cardiac cycle. Diastolic pressure is the minimum pressure on the arteries when the ventricles are relaxing. The standard values of systolic and diastolic pressures for a resting healthy adult are 120mm Hg and 80mm Hg respectively. Usually written as 120/80 mm Hg and read as one twenty over eighty. The systolic and diastolic pressures are not fixed and they may undergo natural variations from one heart beat to another. They are related to the factors such as stress, disease, nutritional factors etc. Hypertension is the condition in which the arterial pressure of the patient is abnormally high whereas hypotension is the condition where the arterial pressure is abnormally low. The difference between systolic and diastolic pressure is called pulse pressure and the standard value is 40mm Hg.

Blood pressure (BP) is one of the most commonly measured physiological parameter. Normally we classify blood pressure measurements into two categories – Indirect (Non Invasive) blood pressure measurement and Direct (Invasive) blood pressure measurement.

Human Respiratory System - functions, parts and parameters

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The respiratory system provides a means for acquiring oxygen (O2) and eliminating carbon dioxide (CO2). Humans have a well developed respiratory system and respiration involves inspiration (breathing in) and expiration (breathing out) exchange of gases in the lungs and its transport to the tissues.

Types of Respiration:

Respiration is the interchange of gases between an organism and the medium in which it lives. Respiration is divided into two types.
Internal Respiration: It is the exchange of gases between blood stream and nearby cells.
External Respiration: External or lung respiration is the exchange of gases between lungs and blood stream. The respiratory rate, respiratory volume, respiratory air flow etc are important variables of respiration.
The mechanism of breathing involves the action of muscles that change the volume of the thoracic cavity (chest) to generate inspiration and expiration. Inspiration results from the contraction of diaphragm and intercostals muscles whereas the expiration results from their relaxation.

Functions of Respiratory System:

1. It helps to avoid sudden changes in blood pH and body fluids.
2. The respiratory organs provide maximum surface area for diffusion of oxygen and CO2.
3. With the help of respiratory system, gases are constantly renewed.
4. Respiratory system protects the surface membranes from harsh environments such as temperature.

Parts of Respiration:

The main parts of respiration are given in the block below.

The function of each block is discussed below.

1. Nose and nasal cavities: The air from outside to inside and vice-versa is guided through the nose and nasal cavities. Actually nose provides the entry of air during inspiration and exit of air during expiration.

2. Pharynx (Throat): The throat is subdivided into three parts – Nasopharynx, Oropharynx, Hypopharynx.

3. Larynx (Voice Box): The vocal cords are located in the larynx. It is called voice box because it is due to the vibration of vocal cords when air is forced upwards, that the sound is produced.

4. Trachea (Windpipe): It is a vertical tube that allows the passage of air to and from the lungs.

5. Bronchi: Trachea is divided into two branches which divide into each lung. Each branch is called bronchus.

6. Bronchioles: The bronchi is also divided into many smaller branches. Bronchioles are the smallest bronchial branches. Air inspired through nose passed through the trachea and which divided into bronchi and terminates at the bronchioles.

7. Alveoli (air sacs): The air sacs trap the air and allow the exchange of gases to blood capillaries. Alveoli have a maximum capacity of around 9L in adult men and 7L in adult women.

8. Lung capillaries: The alveoli is surrounded with thin tubes carrying blood. These are called lung capillaries and they allow the exchange of gases.

9. Lungs: The lungs consists of two cone shaped spongy organs that contain the alveoli (air sacs) that trap the air for gas exchange with blood. Blood enters the lungs through pulmonary arteries and after oxygenation it leaves through pulmonary veins.

Parameters of Respiration:

The parameters of respiration indicate the state of the respiratory function and the lung volumes and capacities under specific conditions. The various parameters of respiration are discussed below. Several factors can affect the lung volumes. A person who is born and lives at sea level will develop a slightly smaller lung capacity than a person who lives at high altitude levels. Also taller people, non-smokers and athletes are found to have more lung capacity when compared to shorter people, smokers and non – athletes respectively. Also the various values vary with the age of the person. In conditions such as asthma the volumes are normally lower but the flow rates are normally obstructed.

1. Dead air (About 150 mL): We know that the air enters the lungs through nose and the nasal cavities. Only a certain portion of air entering the respiratory system reaches the alveoli. The volume of air that is not available for gas exchange with the blood is called dead air.

2. Tidal Volume (TV – Male 500 Ml/ Female 390 mL): It is called the depth of breathing and it is defined as the volume of gases inspired or expired during each respiratory cycle. In other words it is the volume of air an individual is normally breathing in and out.

3. Inspiratory Reserve Volume (IRV Male 3L/ Female 2.3 L): It is the maximum amount of gas that can be inspired with effort from end inspiratory position. Or it is the extra inspiration from low peak tidal volume. It is also called ‘complemental air’.

4. Expiratory Reserve Volume (ERV – Male 1.2L/ Female 0.93 L): It is the maximum amount of gas that can be expired from end expiratory level. Or it is the extra expiration from low peak tidal volume.

5. Residual Volume (RV – Male 1.2L / Female 0.93L): Even if we expire with maximum effort some amount of gas remains in lungs. Residual volume is the amount of gas remaining in lungs after maximal expiration.

6. Total Lung Capacity (TLC – Male 6L/ Female 4.7L): It is the amount of gas contained in the lungs at the end of maximal inspiration. It is the sum of Inspiratory Capacity (IC) and Functional Residual Capacity (FRC). Inspiratory capacity is defined as the maximal amount of gas that can be inspired from resting expiratory level. It is about 3.6 L. Functional Residual Capacity (FRC) is the amount of gas containing in lungs at resting expiratory level. TLC = FRC + IC

7. Minute volume (MV): It is the volume of air breathed for one minute.

8. Vital Capacity (VC – Male 4.6L/ Female 3.6 L): Vital Capacity is the maximum amount of air that a person can expel from the lungs after first filling the lungs to their maximum extent. It is equal to the sum of Inspiratory Reserve Volume (IRV), Expiratory Reserve Volume (ERV) and Tidal Volume (TV). So, VC = IRV+ERV+TV.

Spirometer Working Principle

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Spirometer is the most widely used instrument for the measurement of various lung capacities and respiratory volume.

Working Principle:

As told the spirometer is an apparatus for accurately measuring the volume of air inspired and expired by the lungs. The standard spirometer consists of a movable bell inverted over a chamber of water. To balance the bell jar we use a weight to maintain the gas inside the atmospheric pressure. The height of the bell jar above the water will be proportional to the amount of gas inside it. A breathing tube is connected to the mouth of the patient with the gas under the bell.

When no one is breathing into the mouth piece, the bell will be at rest with a fixed volume above the water level. When the patient expires the pressure inside the bell increases above the atmospheric pressure causing the bell to rise. Similarly when the patient inspires, the pressure inside the bell decrease below the atmospheric pressure and the bell drops down.

As the change in bell pressure changes the volume inside the bell, the position of the bell jar is varied with respect to the inspiration and expiration. As the bell position varies, the position of the weight which balances the bell jar also varies. A pen is attached to the weight in order to record the volume changes in a piece of graph paper. The chart recorder is called spirograph or kymograph and it is a rotary drum. The graph obtained corresponding to breathing is called spirogram.

Some spirometers also have the provision to offer an electrical output that is analog equivalent of the spirogram. Here we connect the pen and weight assembly to a linear potentiometer. If we connect certain positive and negative potentials to the end of the potentiometer, then the resulting electrical output can provide the same data as the pen. When the patient is not breathing the output will be zero. When the patient inspires the output will have one polarity and it will be of opposite polarity during expiration.

Spirometers are one of the primary equipments used for PFT meaning Pulmonary Function Tests. It is a useful test for assessing the health conditions of the patient’s lungs. In addition, it is often used for finding the cause for shortness of breath, analyzing the effects of contaminants on lung functions, effect of medication, and progress for disease treatment.

Tuesday, 19 December 2017

Impedance pneumography

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It is an indirect method used for the measurement of respiratory rate. It is comparatively simpler method because it does not require any placement of mask on the face, fixing of tubes etc. In this method we place only an electrode over the thorax region of patient.

We know that the impedance of the skin of thoracic region changes during respiration depending on the depth and rate of respiration. In this method we are actually measuring the change of impedance of the skin using typical circuits. The motion artifacts can be minimized using a self adhesive type electrode.

Block diagram of impedance pneumograph measurement technique is shown. Here a low voltage ac signal is applied to the chest of patient through surface electrodes. High value fixed resistors connected in series with each electrode create a constant ac current source. Usually the current through the patient’s chest is very small.

Advantages of impedance pneumograph:

1. Artifacts can be easily recognized
2. Electrically safe
3. Equipment is easy to use
4. The ability to obtain ECG from same electrode makes it useful during surgical anesthesia.
5. It is comfortable to the patient

The equivalent circuit of measurement technique is shown below.

The voltage drop across the resistance represents the patient’s thoracic impedance

E0 = I(R + ΔR), where E0 is the output voltage in Volts.
I = Current through the chest in Ampere.
R = Chest Impedance without respiration in Ohms.
ΔR = Change in chest impedance caused by respiration in Ohms.

The signal E0 is amplified by the ac amplifier and applied to a synchronous AM detector. Amplitude variations in E0 are caused due to change in resistance (ΔR) which changes the respiration waveform. A LPF is used after the synchronous detector to remove carrier signal. DC amplifier after LPF is used to increase the output waveform up to a level as required by the display device.

Types of Ventilator Modes

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There are mainly three different types of Ventilators:

A. Assist mode:

In the assist mode, the patient is able to control their breathing. But they are unable to take sufficient amount of air. So in the assist mode the inspiration can be triggered by the patient’s attempt to breath. So the ventilator help the patient to inspire when he wants to do so.

B. Control mode:

This type of ventilators are required especially for the patients who are unable to breath theemselves. Here the breathing is controlled by a timer set to provide desired respiration rate. In this mode the ventilator has complete control over the patient’s respiration.

C. Assist Control mode:

It has the features of both assist mode and control mode. As in assist mode, here also the ventilator is triggered by the patient’s attempt to breath. If the patient fails to breath within a predetermined level, the control mode come into action and the timer automatically triggers the device to inflate the lungs. This mode depends on the patient’s physical condition. Patient can breath as long as he can, and when he fails to do so, the machine takes over the control. The assist – control mode is mainly used in critical care settings.

The ventilators are also classified into the following types depending on the inflation of lungs.

a. Pressure cycled ventilators: In some patients the pressure of the breathed air will not be the specific peak airway pressure. In pressure cycled ventilators, the inflation of lungs continues till the delivered gas to the patients reaches a predetermined level of pressure.

b. Volume cycled ventilators: Due to various lung disorders caused due to smoking problems, some patients cannot inspire upto the desired volume. In volume cycled ventilators, the ventilation of lungs continues till a specified volume of gas has been delivered to the patient. Advantages of volume – cycled ventilation are the selection of variable modes of ventilation, improved patient-ventilator synchronism etc. Also the tidal volume can be simply adjusted.

c. Time cycled ventilators: As the name implies, the patient is supplied with oxygen and other gases for a certain period of time. Time – cycled ventilation occurs as the inspiratory phase begins and gas flows through the ventilator circuits into the patient’s lung until a timing mechanism in the ventilator reaches a preset level. Once the preset time is reached, the inspiratory phase ends and the patient passively exhales. During time-cycled ventilation tidal volume is not controlled directly. The ventilator delivers a tidal volume dependent on gas flow rate. The gas flow rate has to be adjusted to maintain a desired tidal volume and limit peak inspiratory pressure.

Microprocessor based Ventilators

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Microprocessor based Ventilators
In a microprocessor based ventilator, the microprocessor will assist for ventilation. A gas consumption meter is attached to the microprocessor   . This unit will monitor the patient’s ability to breath naturally by monitoring the gas consumption. If the gas consumption is low it indicates that the patient is unable to breath himself. So if the gasconsumption degrades below a desired value, this unit will issue control signals to the micrprocessor. The micrprocessor in turn issue trigger signals to the servo ventilator which is connected to the patient. Lung machine is also connected to the patient to measure various respiration parameters. If the parameters measured are not satisfactory enough, the lung machine unit can also trigger the microprocessor to activate servo ventilator.

Respiratory Therapy Equipments

Under certain conditions some patients may be incapable of breathing in natural means. So they will be provided with mechanical assistance so as to deliver sufficient oxygen to the organs and tissues of the body. Respiratory therapy is a biomedical field in which mechanical assistance is provided for patients in respiration. Also some patients require higher than normal concentration oxygen. It is also provided by respiration therapy.

Oxygen therapy is a means for providing oxygen for the treatment of various conditions resulting from oxyen deficiency. The conditions can be a major heart failure, blood leakage, complicated conditions due to surgery etc. The required oxygen is provided to the patient from an oxygen cylinder through nasal catheters, masks, funnels etc. In some special cases the oxygen is introduced to the patient with medicine such as in nebulizer. If the humidity of the oxygen is to be increased it can be done by using a humidifier.


Inhalators are devices used to supply oxygen or some other therapeutic gases to the patient. It is mainly used in the treatment of conditions such as asthma. Normally inhalators are used when the concentration of oxygen higher than that of air is required
2.Ventilators and Respirators:

Ventilators are used when artificial ventilation is to be provided to the patient for a long time. It is otherwise called a respirator. The main function of respirator is to ventilate the lungs similar to natural ventilation as possible.Ventilators can be of positive pressure ventilators or negative pressure ventilators. The primary indications that a patient needs artificial ventilation are inadequate breathing on the part of the patient which results in lowerd blood oxygen levels. Mechanical ventilation is applied to adjust alveolar ventilation to a level that is as normal as possible for each patient.

a. Positive – pressure ventilators: Most ventilators used normally in positive pressure condition where the inspiratory flow is generated by applying a positive pressure greater than the atmospheric pressure. The air is expired passively. Positive – pressure ventilation is commonly used in ICU and CCU units.

b. Negative – pressure ventilators: It is mostly used in weak and paralyzed patients, Here negative pressure is produced on peripheral of the patient’s chest and pass on to the core to enlarge the lungs and allow the air to surge in. Today negative – pressure ventilation is used in barely a few circumstances. It offer appropriate option for patients with neuromuscular disorders.


The air or oxygen delivered to the patient during respiratory therapy must be humidified in order to prevent damage to the patient’s lungs. So all respiratory therapy equipments include special devices called humidifiers to humidify the air by bubbling an air stream through a water container. The benefit of using a humidifier includes reducing bacteria and dust particles from air. A respiration humidifier has a humidifying chamber, an inlet for feeding breathing air to be humidified, an outlet for releasing the humidified air.


 Nebulizer is a special device used to administer medication to the people in the form of a mist inhaled into the lung. For the treatment of some respiratory diseases such as asthma it is necessary that the patients is supplied with proper medicines. So in nebulizers, the medication is broken into controllable sized particles. It is done by a jet nebulizer or atomizer. Here the medicine is picked up by a high velocity jet of air or oxygen to break it in the form of aerosol which can be easily inhaled by the patient.

Another type of nebulizer is the ultrasonic nebulizer. Here an ultrasonic device is used to produce high intensity ultrasonic waves so that the medication can be easily disintegrated. The block diagram of Ultrasonic nebulizer is shown below.

Nebulizer offer the advantage  of delivering the medicine directly into the lungs and it is an effective way to administer asthma medicine to young children. The disadvantages of conventional nebulizers are that these devices are bulky and expensive, require alternating current and are not portable.


Aspirator is a device which is used as a part of ventilator or  inhalator to remove mucus and other fluids from the airways so that the patient can breath smoothly. Aspirators are typically used for people such as babies who can’t blow out mucus out. The simplest of nasal aspirators is a bulb syringe, which has a squeezable bulb attached to a narrow neck with an opening. A squeeze of the bulb results in the suck out of mucus.

Monday, 18 December 2017

Application of First law of thermodynamics

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This law is simply a statement of law of conservation of energy for a thermodynamic system. Suppose a quantity of energy ΔQ is supplied to a system. It may change the thermal state of the system and the molecules of the system move more vigorously. As a result the internal energy of the system increases. Let ΔU be the increase in internal energy.

In addition, the mechanical state of the system may change. If the system is kept at constant pressure P and its volume increases by ΔV; the work done by the gas against constant pressure P is given by ΔW = P ΔV. Hence, 

ΔQ = ΔU + ΔW

This is known as the first law of thermodynamics.

In differential form, dQ = dU + dW

Application of First law of thermodynamics

1. Isolated system: It is a system that does not interact with the surroundings. In this case there is no heat flow and the work done is zero. It means ΔQ = 0 and ΔW = 0. Hence ΔU = 0. Therefore internal energy of an isolated system remains constant.

2. A cyclic process: The process in which a system returns to its initial state after passing through various intermediate states is called a cyclic process. In this process the change in internal energy is zero. i.e., ΔU = 0. Hence from first law of thermodynamics.

ΔU = ΔQ – ΔW
0 = ΔQ – ΔW

Hence, in a cyclic process, the amount of heat given to a system is equal to the network done by the system. This is the principle of heat engines whose purpose is to absorb heat and perform work in a cyclic process.

3. Boiling process: When a liquid is heated it absorbs heat and its temperature rises. After some time, a stage is reached, when it starts boiling and changes its phase from liquid to vapour. Due to this change of phase the volume increases and work is done. As the process involves work and heat, first law of thermodynamics can be applied.
Consider the vaporization of mass m of a liquid at its boiling point T and pressure P. Let V1 be the volume of the liquid and V2 the volume of the vapour. The work done in expansion is given by,
ΔW = P ΔV = P(V2- V1)

If L is the latent heat of vaporization, the heat absorbed, ΔQ = mL. If ΔU is the change in internal energy during the process, then,
ΔQ = ΔU + ΔW;  ΔU = ΔQ – ΔW
ΔW = mL - P(V2- V1)
It is to be noted that as pressure remains constant during boiling it is an isobaric process.

4. Melting process: When quantity of heat dQ is given to a solid at its melting point it is converted into liquid. The temperature and pressure remain constant till the whole solid is completely converted into liquid. The internal energy changes during melting.
If m is the mass and L is the specific latent heat of fusion of the solid, then, dQ = mL.
dW = pdV = P(V2- V1); where P is the pressure, V1 the volume of the solid and V2 is the volume of the liquid.

Therefore, mL = dU + P(V2- V1) = dU (since dV = V2- V1 is negligible)

Thermodynamics Lecture Notes

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Thermodynamics is the branch of physics which deals with process involving heat, work and internal energy. Its scope is very wide and covers all branches of science in which heat or some other quantities depending on it play an important role.

System and surroundings

When we study thermodynamics, we focus our attention on a particular region of space or a finite portion of matter. This is called a thermodynamic system. Anything outside the system which has got some bearing on the behaviour of the system is called the surrounding.
To investigate a system there are two kinds of approaches. In one approach called microscopic approach, we go into the details of the internal structure of the system. Here we take into account the properties of atoms and molecules, constituting the system. For example in kinetic theory of matter, the behaviour of a system is explained in terms of the properties of molecules.
In another approach called macroscopic approach we take into account only the properties of the system as a whole without reference to internal structure. Volume, pressure, temperature etc are macroscopic quantities which are measurable. Thermodynamics deals with the bulk property of the system and it does not pay attention to the internal structure.

Thermodynamic variables

The thermal state of a simple homogeneous body is defined by its temperature T, pressure P and volume V. These quantities are called thermodynamic variables or co-ordinates. A particular set of such values specify a particular state of the system. The process by which the system goes from one thermodynamic state to the other is called thermodynamic process. Heating a gas contained in a cylinder fitted with a piston or compressing the gas are familiar examples of thermodynamic process.


When two bodies at different tempratures are brought in contact with each other, the temperature of one body falls while the temperature of the other rises. The process continues until both attain a common temperature. To explain this phenomenon we assume that a certain amount of energy is transferred from the hot body to the cold body. This energy in transit is reffered to as heat. Conventionally heat energy entering a system is said to be positive and that leaving a system is said to be negative. Like any other form of energy, heat energy is measured in Joules.


In mechanics we define work as the product of force and displacement in the direction of force. When we speak of work in thermodynamics we consider only the external work which involves the interaction between the system and its surroundings. Any internal work done by one part of the system on another part is not considered in thermodynamics. In thermodynamics work done by a system is taken as positive and work done on the system is taken as negative. In thermodynamics work is associated with a change in volume.

At the first glance it appears that heat and work are two separate concepts entirely independent of each other; but they are interrelated. Both heat and work are forms of energy and can be transformed from one form into another.

Work done by a thermodynamic system

Consider an ideal gas enclosed in a cylinder fitted with a smooth piston. If the pressure exerted by the gas is P and area of cross section of the piston is A, then force exerted by the gas on the piston is given by, F = PA.

If due to this force the piston moves through a small distance dx, then work done by the gas is given by,

dW = F × dx = P × A × dx = P × dV, where A × dx = dV, the change in volume. If the volume changes from V1 to V2 the total work done is given by,

Internal energy of a thermodynamic system:

According to kinetic theory, a system is made up of large number of particles called molecules. These molecules are constantly in motion and hence possess kinetic energy. Again there exists a force called intermolecular forces between molecules of matter. Due to this force, the molecules possess potential energy. The sum of the kinetic and potential energies of all the molecules of a system is called internal energy. If the temperature of a body increased, its molecular motion increases. Hence the internal energy also increases. When matter changes its phase, its internal energy also changes.

Wednesday, 22 November 2017

Electrocardiogram of the Heart

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An Electrocardiogram of the Heart is the recording of small electric waves being generated during heart activity. The term electrocardiograph is derived from three Greek words 'electro' meaning related to electrical activity, 'cardio' meaning heart, and 'graph' meaning to write. It is used worldwide as a simple way of diagnosing heart conditions.

Electrical activity of heart: In the heart there are specialized cells called pacemaker cells. When the heart muscle is at rest, the pacemaker cells are negatively charged and when the heart contracts they are positively charged. These cells produce small electrical signals b changing their electrical from positive to negative and back. The heart cells have the ability to spread its electrical charge to its adjacent cells. This initial trigger is enough to produce a chain reaction. Thus the electrical activity of heart starts at the top of the heart and spreads down. So this tiny electric shock spreads down to heart causing it to contract. The contraction of heart results in the pumping of blood.

For the cardiovascular system to work properly, the atria and ventricles must operate in proper time relationship. During each cycle of ECG, the action potential in the heart originates near the top of the right atrium at a point called the pace maker or sino-atrial node (SA node). Pacemakers are specialized cells that generate action potentials at a regular rate. It is necessary that to initiate the heart beat, the action potentials generated by the pacemakers propagate in all directions along the surface of atria. These propagating waves terminate at a point near the center of the heart called AV node (Atrio-ventricular node). As told earlier, the action of atria and ventricles must have a proper timing relationship. This is provided by some special fibers at the AV node. These fibers act as a delay line to provide the timing between the atria and ventricles. So after the electrical excitation passes through the delay line, it is spread rapidly to all parts of both ventricles by the bundle of His. Purkinje fibers are special fibers present in the bundle of His.

Usually heart problems can produce a wide range of symptoms. Without the help of ECG it may not be possible to tell whether the symptoms are caused by a heart problem. Symptoms are chest pain, shortness of breath, palpitations, abdominal pain, weakness etc. In some cases ECG reveals a problem that is not cardiac in nature. Ex: Overdose of certain drugs, electrolyte abnormalities etc.

Saturday, 18 November 2017

E-commerce - Challenges, Security Issues, Fundamentals

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Traditional commerce is the term used for the local buying and selling of products. here there is no intermediary service such as internet or others. Some of the products involved in sale or purchase are fashion clothing, food products, jewelry and other products which are available in the local market. While in a E-commerce, sale or purchase of books, online CD'S, delivery of software, advertising and promotion of travel and other services takes place. Also online tracking of shipments is done through E-commerce.

But we can also combine both traditional commerce and E-commerce. The combination of both includes online banking, sale or purchase of automobiles and insurance products. Investment can be also done through the traditional and electronic commerce.


E-commerce can help to increase the profit that is increasing sales and decreasing cost. Some of the challenges faced by e-commerce is explained below.

E-commerce can help to increase the profit, that is increasing sales and decreasing cost. The advertisement provided on the web can help small industries for the purpose of promotion. It will reach all the customers in the world. This help in the increased sale and thus the cost of product can be reduced. Also, the business can use e-commerce in their purchasing process to identify the new suppliers and business parties. This is also a challenge faced by an E-commerce. When we create a site for the purpose of E-commerce, the following factors should be considered.
1. Why do we need to create a site?
2. Who is the visitor for the site?
3. Why do we want our own website for E-Commerce?


Security issues in E-commerce can be classified according to secrecy, integrity and necessity.

1. Necessity Threats: This type of threats will happen due to delay or denial threat. It will disrupt the normal computer processing. A computer that has affected necessity threats slows the processing speed.
2. Secrecy Threats: It is one of the most high security threat. It prevents the unauthorized information disclosure. But the privacy is to the protection of individual rights to non disclosure.
Example: Sniffer programs.
3. Integrity Threats: Unprotected banking transactions are a type of integrity threat. Here the deposited amount transmitted over the internet may sometimes subject to integrity violations may leads to integrity threat.
Example: Cyber Vandalism (replacing data with porn or others).


E-Commerce not only helps to increase the profit by increasing sales and decreasing cost. But also increases the purchasing opportunities for the buyer. This process helps to identify new parties and business suppliers. Thus negotiation of price and delivery terms can be made easier. This is one of the success factors for E-Commerce. Another factor is the buyer can select from a wide range of choices and information available about the product in the web. Also they can customize the level of details about a particular product.

The involvement of E-commerce in the social welfare is also a success factor for the E-commerce. The welfare of the society includes tax refunds, public retirement and so on. This type of electronic payment helps the customer to audit and monitor. This type of transaction can be done at home. Thus we can avoid the transportation cost and save time.


1. Electronic Cash: Electronic Cash must be able to pass transparently across international borders and can be automatically converted to recipient country's currency. It must have a monetary value. Companies offering E-Cash are
a. Check Free: Check Free provides software that permits users to pay all their bills with online electronic checks.
b. Internet Cash: Merchants provide cash rather than credit cards to pay for products for online customers.
c. Pay Pal: Pay Pal provide payment processing services to business and for individuals.
d. Cyber Cash: Cyber Cash includes credit card, micro payment and check payment services.

2. Electronic Payment: Electronic Payment is the first introduced money transfer method. In Early days, it was labeled at Electronic Fund Transfer. The transfer of fund is done through electronic terminals, telephone or computers.

3. Electronic Wallets: It includes credit cards, electronic cash, owner identification and owner address information. Examples are Agile Wallet, Microsoft Wallet and E-Wallets.

4. Stored Value Cards: It consists of a microchip or a plastic card with a magnetic strip. Commonly used stored value cards include Prepaid Phone and Bus Card.
   example: Magnets strip cards, Smart Cards, Mondex Smart Card etc.

Acuwin is one of the leading thiruvananthapuram IT companies providing Software Development and Web Development Services.

Website Development

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Web Developers are the people involved in developing the website. They consists of a team of workers. Their main aim is to satisfy the client's need and to meet the expectation level of client. The web development team consists of  Web Optimizers,Web Designers,Web Programmers and Content Writers. The main duty of designers is to design the web page. They produce prototypes. Dynamic programming section belongs to Web programmers. Content writers write the contents for the website. Web Optimizers optimize the web pages.

Each Worker in the Web Development Company should have their own duty. The web designers produce the prototypes according to the client's need. They design the pages beautifully to attract the visitors.Content Writers write the contents for the website. They construct the sentences simply in order to understand the visitors quickly. Programming is an important part in website development and is done by the web programmers. Optimization is done by the Web Optimizers. Optimizers are the key people in website development. Their duty is to increase the page rank.

Web developers work in co-operation in order to fulfill clients demand. The prototypes built by the developers are reviewed by the team workers and send to client. After demonstration, client will send the feedback of website. According to the feedback, they redesign the web page. After designing, programming and content writing, optimization for website is done.

Acuwin is one of the leading Thiruvananthapuram IT Companies providing Software Development and Web Development Services.

Sunday, 16 July 2017

Isolation Amplifiers

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Isolation amplifiers are used to provide electrical isolation and an electric safety barrier to the patients during measurements. Some patients are highly susceptible to electrical shock hazards. Under certain conditions, these shock hazards can cause very severe effects to the patient. So it is required to protect the patient. The isolation amplifiers can provide very high insulation in the range of about a lack mega ohms! There exist a common mode voltage which are the potential difference between instrument ground and signal ground during measurement. The data acquisition components need to be protected from this common mode voltages because as the magnitude of it increases, the chance of instrument destruction increases. Even if the magnitude of the common mode voltage is low, there is a possibility of noisy representation of the signal under investigation.

Isolation amplifiers are very useful when we need to amplify low level signals in multichannel applications. Also they eliminate measurement errors caused by ground loops.

There are two broad classifications of isolation amplifiers. Some isolation amplifiers provide input-to-output isolation without channel-to-channel isolation. It offers only one isolation barrier for a multichannel instrument. Some other type of isolation amplifiers provide both input-to-output isolation and channel-to-channel isolation.

There are two isolation amplifier specifications.
1. The amplifier isolation breakdown voltage: It is defined as the absolute maximum common mode voltage that the isolation amplifier can handle without damage.
2. The Amplifier CMRR: It is defined as the degree to which the common mode voltage will disrupt the normal mode component measurement.

In addition to these, the frequency of the common mode voltage is also important. Higher frequency common mode voltages can create difficulty for many isolation amplifiers due to the effect of parasitic capacitance.

The basic block in figure which illustrate the working of an isolation amplifier is shown below.

Input amplifier amplifies the input  and the amplified output is applied to a modulatior which modulates the signal by using AM, PWM or any other technique. The isolation barrier is generally an energy converter where the electrical energy of the modulator is converted to some other form of energy (a non-electrical energy). Then the signal is modulated and finally amplified by the output amplifier.

The standard symbol of an isolation amplifier is shown in figure.

Isolation Amplifiers using Optical Isolation

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Normally we use optical isolation barrier in order to reduce the effect of EMI (Electromagnetic Interference) as the optical fibers are not susceptible to EMI.  In Isolation amplifier using Optical isolation, the transducer converts the physiological information into electrical form which is amplified by the isolation amplifier. The amplified output is applied to a voltage to frequency converter. It is done because after voltage to frequency conversion the signals will be in digital form which is ideal for optical transmission. The FOT (Fiber Optic Transmitter) transmits the signal through the optical fiber cable which can provide a high degree of isolation. At the receiving end, the signal is received by a FOR (Fiber Optic Receiver) which feeds the signal to FVC (Frequency to Voltage Converter) to get the original signal.

Bioelectric Amplifiers

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As the name implies, the bioelectric amplifiers are used to amplify the bioelectric signals. The bioelectric signals measured from various body parts are having an amplitude ranging from mVs to µVs. So it is necessary to amplify the extremely low amplitude signals for the analysis of the biological data. It is for this purpose that the bioelectric amplifiers are used. Usually we use operational amplifiers as bioelectric amplifiers due to its high gain and other versatile features.

The bioelectric amplifiers have some properties.

1. The gain of the bioelectric amplifier may be low, medium or high depending on the type of amplifier and the signal to be amplified. For example the low gain amplifiers are used for the measurement of action potential, medium gain amplifiers are used for the amplification of ECG waveform and the high gain amplifiers are used for EEG signal amplification.

2. The bioelectric amplifiers may be ac coupled or dc coupled.

3. The frequency response of a bioelectric amplifier range from very low frequency to high frequency range.

4. Bioelectric amplifiers have differential input and single ended output.

5. High CMRR and extremely high input impedance.

Two important parameters of bioelectric amplifiers are noise and drift. We have to avoid the effect of both these parameters on bioelectric amplifiers. Drift is the change in output due to the change in temperature. Noise is the thermal noise generated in electronic devices. Both these problems can be avoided by proper design to make the bioelectric amplifier more effective.

LVDT - Advantages and Disadvantages

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As shown in figure, LVDT consists of a transformer with one primary winding and two secondary windings. Here the secondary windings are connected in such a way that their induced voltages oppose each other. An alternating current is driven through the primary, causing a voltage to be induced in each secondary proportional to its mutual inductance with the primary. An iron core is located in between the primary and secondary windings.If the core is at the central position, the voltages in the two secondary windings are equal and hence the output is cancelled. When the core is displaced in one direction, the voltage in one coin increase as the other decreases causing the output voltage to increase from zero to maximum. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero to maximum, but its phase is opposite to that of primary. Thus the magnitude of the output voltage will be proportional to the distance moved by the core and it is why the device is called linear. The phase of the voltage indicates the direction of the displacement.

Advantages of LVDTs

1. The sliding core does not touch inside the tube and hence it can  move without friction.
2. As friction is avoided, the output will be accurate in almost all cases.
3. There is no sliding or rotating contacts which improves the efficiency.
4. Very high resolution
5. Simple in construction
6. Easy to align and maintain
7. Light in weight

Disadvantages of LVDTs

1. Large displacements are required for differential output
2. Sensitive to stray magnetic field
3. It is sensitive to temperature variations.

Tuesday, 20 June 2017

Capacitive and Inductive Transducers

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Capacitive Transducers:

Capacitive transducer is a measurement device in which variations in pressure upon a capacitive element proportionally change the element’s capacitive rating and thus the strength of the measured electric signal from the device. As we know here the capacitance of the transducer varies with respect to the external stimulas. Normally a capacitive transducer uses a stationary plate and a movable plate. The stationary and the movable plates are separated by aair or vacuum dielectric. The movable plate changes its position under the influence of an external stimulus. As we know the capacitance depends on the area of plates, the movement of plate causes a change in capacitance. This is the basic working principle of a capacitive transducer.

Advantages of Capacitive transducers:

Compared with optical, piezo-resistive and inductive transducers, capacitive transducers have many advantages.
1. Low cost,
2. Less power usage,
3. Good stability,
4. High resolution,
5. Better speed,
6. Good frequency response
7. They require very little force to operate..

Disadvantages of Capacitive transducers:

1. The performance is severely affected by dirt and contaminants as they change the dielectric constant.
2. They are sensitive to temperature variations
3. Metallic parts must be insulated from each other

Biomedical Application:

1. It is mainly used for blood pressure measurements.
2. Also used for displacement or position measurement.
3. They can detect motion, acceleration, flow and many other variables.

Inductive Transducers:

The inductance of a coil can be changed either by changing its physical dimension or by changing the effective permeability of its magnetic core. In transducers using inductive elements we normally use the second principle. The effective permeability can be changed by moving a core, which is having a permeability higher than, the air through the coil. But the disadvantage with basic type of inductive transducer is that the inductance of coil is not related linearly to the displacement of coil if large displacements occur accidently. It is to avoid this disadvantage that we use LVDTs. The existing inductive transducers have a relatively small output power and often require amplification of their outputs.

Transducers and Sensors

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A transducer is a device that performs the conversion of one form of variable into another. Normally in biomedical applications, the transducer input is in non-electrical form and the output will be in electrical form. Actually transducers and electrodes are a part of a group of devices called sensors. Major difference between transducers and electrodes is that transducers make use of some transducible element for the measurement. But the electrodes directly measure the signals. A sensor means a device used to measure a particular parameter either by changing the desired signal to electrical signal or by changing ionic flow into electron flow.

Two types of principles are involved in the process of converting non-electrical variable into electrical signal. Depending on these principles the transducers are mainly classified into two types. - Active transducers and Passive transducers


An active transducer is one which gives its output without the use of excitation voltage or modulation of a carrier signal. One property of active transducer is that it converts non-electrical energy into electrical energy and vice-versa.
The various types of active transducers are
a.Magnetic induction type transducers
b. Piezoelectric type transducers
c. Photovoltaic type transducers
d. Thermoelectric type transducers

A. Magnetic induction type Transducers:

We know that when an electrical conductor is moved in a magnetic field in such a way that flux through the conductor is changed, a voltage is induced. The induced voltage will be proportional to the rate of change of magnetic flux which in turn is proportional to the conductor movement.. The induced emf is given by, e = Blv

Biomedical Applications:
1. These type of transducers are used in electromagnetic flow meters to measure blood flow.
2. Also used in heart sound microphones.

B. Piezoelectric type transducers:

Piezoelectricity is the ability of some materials to generate an electric field or electric potential in response to applied mechanical stress. The effect is related to a change of polarization density within the materials volume and is also reversible-means the production of stress or strain when an electric field is applied. A piezoelectric crystal (such as Quartz) can produce a voltage under deformation by compression or tension. This is called piezoelectric effect. This effect is the basic working principle of piezoelectric type transducers. So they convert displacement or pressure into an electrical variable.

Biomedical Application:
Mainly used in pulse sensing measurements.

C. Photo voltaic type of transducers:

Photoelectric effect is the ejection of electron from a metal or semi conductor surface when it is illuminated by light or any other radiation of suitable wavelength. So a photoelectric transducer generates electrical voltage in proportion to the radiant energy incident on it.

Biomedical Application:
Used in pulse sensors.

D. Thermoelectric type transducers:

These types of transducers are based on the seeback effect. It states that when two junctions of a thermocouple are maintained at different temperatures, an emf is generated which wil be proportional to the temperature difference between the junctions. Thermocouples are widely used type of temperature sensor for measurement and control. They are inexpensive, interchangeable and are supplied with standard connectors and can measure a wide range of temperatures. Also we can use thermistors as active transducers. Here its resistance value changes with change in temperature. The material used in a thermistor is usually a ceramic or polymer.

Advantages: Small size, Low cost, Fast response, Wide temperature range, High accuracy

Disadvantages: Thermistors are unsuitable for wide temperature ranges, Less stable at high temperatures, Non-linear temperature-resistance curve.

Biomedical Application:
1. Used in the measurement of physiological temperature
2. In biotelemetry systems to measure temperature.


Passive transducers convert the physiological parameter (such as blood pressure, temperature etc) into an electrical output using a DC or AC excitation voltage. One important property of the passive transducers is that they are not reversible. Passive components such as resistors, capacitors, inductors are used to make the passive transducers. They require an external power to operate and the output is a measure of some variation in the passive components.

Wheatstone Bridge
Many transducers make use of the principle of Wheatstone bridge. In many biomedical transducers using Wheatstone bridge, all four resistances are equal under balanced condition. The balanced condition is varied when any of the resistances varies. Normally during the measurement, it is designed in such a way that the resistance value of a particular resistance varies and hence balance is lost. By analyzing this change in resistance, the parameter can be measured indirectly.

Friday, 2 June 2017

CRO and its Applications

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An oscilloscope is previously called as an oscillograph. It can be informally known as a scope, CRO (for cathode-ray oscilloscope), or DSO (for the more modern digital storage oscilloscope). It is a type of electronic test instrument that allows observation of constantly varying signal voltages. The output of a CRO will be usually as a two-dimensional graph of one or more electrical potential differences using the vertical or y-axis, plotted as a function of time (horizontal or x-axis). Many signals (e.g. sine, cosine etc) can be converted to voltages and can be displayed this way. By changing the mode of CRO into transfer characteristics, we can see the transfer characteristics of signals. The transfer characteristics of a signal give the variation of the output wave with respect to the variation to the input wave. The Signals may be either periodic or repeat constantly, so that the multiple samples of a signal which is actually varying with respect to time can be displayed as a steady picture in the CRO. Many oscilloscopes (storage oscilloscopes) are able to capture non-repeating waveforms for a specified period of time, and are able to produce a steady display of the captured segment.

Oscilloscopes are mainly used to observe the correct wave shape of an electrical signal. Oscilloscopes are usually calibrated so that the two axes voltage and time can be easily read as well as possible by the eye. This will yields to the measurement of the peak-to-peak voltage of a waveform. It also allows checking the frequency of periodic signals, the time between pulses, the time taken for a signal to rise to full amplitude, which is usually called as the rise time, and relative timing of several related signals.

The applications of Oscilloscopes are in the fields of sciences, engineering, medicine, and telecommunications industry. For the maintenance of electronic equipment and laboratory work, general-purpose instruments are used. Special-purpose oscilloscopes are used for analyzing an automotive ignition system or to display the waveform of the heartbeat as an electrocardiogram. If we consider some practical example, some computer sound software allows the sound being listened to be displayed on the screen as by an oscilloscope. Thus CRO can be used in many applications in the emerging world technologies. Most of all, the CRO can be considered as the eye of an electronic engineer. In other words an electronic engineer cannot see his outputs without the help of a CRO.

Some special storage CRTs are used to maintain a steady display of a single brief signal in case of advanced storage oscilloscopes. By digital storage oscilloscopes (DSOs) with thin panel displays, fast analog-to-digital converters and digital signal processors, CROs were later largely outdated. DSOs without integrated displays are known as digitizers. Digitizers are available at lower cost, and it uses a general-purpose digital computer to process and display the required waveforms.