Friday, 29 December 2017

Non Invasive Blood Pressure Measurement

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.

Wednesday, 20 December 2017

Systolic Pressure and Diastolic Pressure

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

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

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

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

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

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

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

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.