Biomedical Instrumentation

Archive for September, 2009

High Frequency Heat Therapy: Physical stimulus commonly employed in the practice of physiotherapy is in the form of heat, either by simple heat radiation or by the application of high frequency energy obtained from special generators. The use of high frequency energy in thermotherapy has the advantage of considerable penetration as compared with simple heat application. Thus, with high frequency energy, deeper lying tissues can be provided heat. High frequency therapy is based on the fact that the dipole molecules of the body are normally placed randomly. Under the influence of an electric field, they rotate according to the polarity of their charge in the direction of the field lines.

The positively charged end of the dipole then orients itself to the minus pole and negatively charged end to the plus pole. Since the polarity of the electric field alternates, a micro-heating effect results from the continuous re-alignment of the molecules. High frequency energy for heating is obtained by various ways. It may be from the short-wave therapy unit making use of either the condenser field or the inductor field method. Microwave and ultrasonic waves are also used for heating purposes in special cases.

Microwave Diathermy: Microwave diathermy consists in irradiating the tissues of the patient’s body with very short wireless waves having frequency in the micro wave region. Microwaves are a form of electromagnetic radiation with a frequency range of 300-30000MHz and wavelengths varying from 10mm to 1mm. In the electromagnetic spectrum, microwaves lie between short waves and infrared waves. The heating effect is produced by the absorption of the microwaves in the region of the body under treatment. Microwave diathermy provides one of the most valuable sources of therapeutic heat available to the physician.

However, in many conditions, though the therapeutic effects of microwave diathermy are similar to short-wave diathermy, yet in others, better results are obtained by using microwave. The technique of application of microwave diathermy is very simple. Unlike the short-wave diathermy where pads are used to bring in the patient as a part of the circuit, the microwaves are transmitted from an emitter, and are directed towards the portion of the body to be treated.

Apex cardiograph: An apex cardiograph records the chest-wall movements over the apex of the heart. These movements are in the form of vibrations having a frequency range of 0.1 to about 20 Hz. The transducer required for recording these movements is similar to that employed for a phonocardiography but which has a frequency response much below the audio range. It can be air coupled microphone or a contact microphone. The apex cardiograph has limited applications. It is, however, useful in the diagnosis of the enlargement of the heart chambers and some type of valvular disorders.

Ballistocardiography: A ballistocardiography is a machine that records the movement imparted to the body with each beat of the heart cycle. These movements occur during the ventricular contraction of the heart muscle when the blood is ejected with sufficient force. In BCG, the patient is made to lie on a table top which is spring suspended or otherwise mounted to respond to very slight movements along the head axis. Sensing devices are mounted on the table to convert these movements into corresponding electrical signals. The sensors usually are piezo-electric crystals, resistive elements or permanent magnets, moving with respect to fixed coils. In all such cases, the output of the sensor is amplified and fed to an oscilloscope or to a chart recorder. BCG has so far been used mainly for research purpose only. It is rarely used in routine clinical applications.

Electroretinograph: It is found that an electrical potential exists between the cornea and the back of the eye. This potential changes when the eye is illuminated. The process of recording the change in potential when light falls on the eye is called Electroretinograph. ERG potentials can be recorded with a pair of electrodes. One of the electrodes is mounted on a contact lens and is in direct contact with the cornea. The other electrode is placed on the skin adjacent to the outer corner of the eye. A reference electrode may be placed on the forehead. A general purpose direct writing recorder may be used for recording electroretinograms.

Intermittent treatment with a mechanical device like the artificial kidney will reduce the accumulation of waste products and water and thus the blood concentrations of the toxic substances are returned to normal levels. By effectively removing these materials from the blood, the dialyzer temporarily replaces the function of the natural kidney is a dialyzing unit which operates outside the patient’s own body. It receives the patient’s blood from the cannulated artery via plastic tubing. The return of the dialyzed blood is by another plastic tube to an appropriate vein.

The artificial kidney is thus simply a membrane separation device that serves as a mass exchanger during clinical use. It is unable to perform any of the synthetic or metabolic functions of the normal kidney and, therefore, cannot correct abnormalities that result from the loss of these functions. The only use of the artificial kidney in replacing renal function, therefore, is the transfer of noxious substances from the blood to the dial sate, so that they might be eliminated from the body. The dialyzer is the part in the artificial kidney system in which the treatment actually takes place and where the blood is freed from the waste products.

It is the meeting point of two circuits, one in which the blood circulates and the other in which dialysis fluid flows. Dialyzer, in routine clinical use, may be classified according to three basic design considerations: coil, parallel plate and hollow fiber type. Each type of dialyzer has certain optimum operating requirements. The rate of clearance of substances such as urea, creatinine, etc. from the blood during passage through an artificial kidney is dependent upon the rate of the blood flow.

As the flow rate falls, there is a disproportionate fall in clearance. At high flow rates, there is little advantage in further augmentation of the blood flow. The rate and pattern of the dialysate flow also influence overall performance in respect of clearance of waste products. Almost all commercial dialyzers use cellulosic type membranes, the most common being Cuprohon. My dear friends! I am sure this article will enhance your knowledge regarding the artificial kidney.

Related to the measurement of the blood flow is the measurement of volume changes in any part of the body that results from the pulsation the diagnosis of arterial obstructions as well as for pulse-wave velocity measurements of these volume changes, or phenomena related thereto, is called plethysmography. True plethysmography is one that actually responds to changes in volume. Such an instrument consists of a rigid cup or chamber placed over the limb or digit in which the volume changes are to be measured. The cup is tightly sealed to the member to be measured so that any changes of volume in the limb or digit reflect as pressure changes inside the chamber. Either fluid or air can be used to fill the chamber.

Plethysmography may be designed for constant pressure or constant volume within the chamber. In either case, some form of pressure or displacement transducer must be included to respond to pressure changes and to provide a signal that can be calibrated to represent the volume of the limb or digit. The base line pressure can be calibrated by use of a calibrating string. This type of plethysmography can be used in two ways. If the cuff, placed upstream from the sealed, is not inflated, the output signal is simply a sequence of pulsations proportional to the individual volume changes with each heart beat .The plethysmograph can be used to measure the total amount of blood flowing into the limb or digit being measured.

By inflating the cuff to a pressure just above venous pressure, arterial blood can flow past the cuff, but venous blood cannot leave. The result is that the limb or digit increases its volume with each heart beat by the volume of the blood entering during that beat. Another device that quite closely approximates a true plethysmograph is the capacitance plethysmography. In this device, which is generally used on either the arm or leg, the limb in which the volume is being measured becomes one plate of capacitor. The other plate is formed by a fixed screen held at a small distance from the limb by an insulating layer.

In order to reduce the likelihood of electrical accidents, a number of protective methods have evolved. Some are used universally, some are required in areas that are generally considered especially hazardous, and still others have been essentially for the use in hospitals.

Grounding: Protection by grounding, however, has several shortcomings. Obviously, it is effective only as long as a good ground connection exists. Experience has shown that many receptacles, plugs, and line cords of the conventional type do not hold up under the conditions of the hospital use. Many manufacturers now make available hospital grade receptacles and plugs which are designed to pass a strict test required by the underwriters’ laboratory for devices to qualify for this specification. A second disadvantage is that in the case of a short, protection is provided by removing the power from the defective device by tripping the circuit breaker. This action, however, also removes the power from all other devices connected to the same branch circuit. In a hospital setting, one defective device could disable a number of other devices, which might include life-saving instruments.

Double insulation: In double-insulated equipment the case is made of non-conductive material, usually a suitable plastic. If accessible metal parts are used, they are attached to the conductive main body of the equipment through a separate layer of insulation in addition to the insulation that separates this body from the electrical parts. The intention of this method is to assure that the fault resistance is always large. Double-insulated equipment need not be grounded, and therefore it is usually equipped with the plug that does not have a ground pin. Equipment of this type must be labeled double insulted. Double insulation is now widely used as a method of protection in hand-held power tools and electric-powered garden equipment such as lawn mowers. However, double insulation is of only limited value for equipment found in a hospital environment. Unless the equipment is also designed to be waterproof, the double insulation can easily be rendered ineffective if a conductive fluid such as saline or urine is spilled over the equipment or if the equipment is submerged in such a fluid.

Definitions of drug abuse vary. The medical community and the FDA have created one set of formal definitions; society has created another set; and individual people have created others that reflect their own drug histories and attitudes. The FDA makes these distinctions: drug use is the taking of a drug as medicine, correctly-that is, for a medically intended purpose, and in the appropriate amount, frequency, strength, and manner. In contrast, drug abuse is the deliberate taking of a drug for a non medical purpose and in a manner that can result in damage to a person’s health and ability to function. Both legal and illegal drugs can be abused.

The FDA also defines drug misuse as the taking of a drug for its medically intended purpose, but not in the appropriate amount, frequency, strength, or manner. Recreational use of drugs is not defined by the FDA. Medical terminology describes drug abuse simply as any non-medical use or overuse of any drug. These definitions classify any use of drugs for non-medical reasons as drug abuse; there is no such thing as mere use for example, to produce pleasure or hallucinations. Medically speaking, then, a person who drinks alcohol excessively to get high or who uses tobacco is abusing a drug. Someone who takes too large a dose a prescription or over-the-drug is misusing the drug. Such drug misuse can lead to drug abuse.

Different factors may lead people to abuse drugs. Among them are the nature of the person, the legal consequences, and the nature of the drug. The nature of a person influences the person’s relationships with drugs in several ways. One is genetic, or physical. Some researchers are looking to people’s genetic make ups in hopes of finding inborn tendencies toward drug abuse. Others are exploring the personalities of youngsters to identify traits that predict such tendencies. These traits may be hereditary, may result from the way parents raise their children, or both.

Curiosity can be strong motivator drug abuse. Some people try drugs to see what they are like. Of these who experiment, some continue to use drugs and become drug dependent. The desire to fit in socially motivates many people to abuse drugs. Drugs are often part of social events. Everyone needs to have a sense of belonging to some group, and drug-taking can provide a reason for being together. My dear friends! I am sure this article is useful and that will enhance your knowledge regarding why people do people abuse drugs.

Dear friends! Seeking pleasure is an inborn instinct, universal to all creatures on earth. In nature, this instinct normally drives creatures to act in ways that benefit them without harming them. Eating is a pleasure that, in nature, leads to nourishment of the body. Sexual activity is pleasurable and leads to propagation of the species. Exercising and then relaxing after exertion are pleasurable, and lead to improved fitness and high energy. All of these activities can themselves be abused, and can lead to harm-overeating cause’s obesity; indiscriminate sexual activity can lead to unwanted pregnancy and sexually transmitted disease, and over exercising can lead to injury.

All these concerns are addressed elsewhere in the book; the point here is that reasonable pleasure seeking by healthy means is beneficial, but that obsessive pleasure seeking through risky behaviors can be harmful. The acts of eating, engaging in sexual activity, exercising, and relaxing produce pleasure by stimulating the brain to produce endorphins, pleasure producing chemicals. These chemicals are similar to mind-altering drugs, but there is a key difference- they are continuously produced in response to healthy activities. The taking of a mind-altering drug produces pleasure directly in the brain, but intermittently, and causes the brain to produce fewer endorphins on its own.

When the effects of the drug wear off, there is a lack of endorphin production. The drug-taker feels the low endorphin concentration as an unpleasant sensation, known as dysphoria. The person may then use drugs to chase away the dysphoria, unaware that the unpleasant feelings are the after effects of the drugs themselves. A drug is physiologically addictive if, when it is withheld, brainwave patterns change, mood alters, and drug-seeking behavior follows. Physiological addiction also involves tolerance, necessitating increasing doses.

Physiological addiction always has a psychological component a strong carving for the drug. But psychological addiction can occur without physiological addiction, and the craving can be for some other habit or behavior, such as excessive sexual activity, overwork, or over exercise. Almost any behavior can be employed in psychological addiction, and such an addiction can be as powerful as a physiological addiction. My dear friends! I am sure this article will enhance your knowledge regarding the effect of drug addiction.

People of certain religious groups have remarkably low cancer rates, and scientists have studied them to find out why. One such group, the Seventh Day Adventists encourages a vegetarian diet. Of course, abstinence from tobacco and alcohol accounts for a large part of the low cancer rate; still, the group’s cancer incidence is only half what would be expected in people who do not smoke or drink alcohol. These and other studies have led researchers to identify three dietary factors strongly associated with high cancer risk; high meat and fat consumption, low vegetable consumption, and low grain consumption.

Vegetarian-type diets are probably protective against certain types of cancers, particularly colon cancer, one of the major health problems in the modern world. The fat, and perhaps the excess protein, in meat may act as cancer promoters. In addition, any meat that has been smoked, charbroiled, burned, or commercially cured may contain carcinogens. Research also suggests that fibers present in vegetables and grains protect against cancer of the large intestine, probably by trapping carcinogens in the digestive tract and hastening their excretion. Further, evidence suggests that the vitamins that occur in fruits and vegetables may help to prevent the development of certain cancers.

For example the vitamin C of say, oranges may stop the formation of carcinogens called nitrosamines; and the vitamin A of vegetables and fruits such as sweet potatoes and peaches is important in preventing cancers of the body’s external and internal linings, including the skin and lungs. The fibers of plant foods such as whole grains, fruits, and vegetables may play roles as well. Other nutrient candidates for roles in cancer prevention are the vitamins riboflavin and folate, the mineral calcium, and a group of non vitamins found in the cabbage family.

Taken in whole foods, these arrive in the body together with many other nutrients. A word of caution though; these benefits come from foods, not supplements. Some people promote the sales of useless vitamin and mineral preparation as cancer fighters. Don’t waste money on nutrition supplements that provide a false hope of cancer prevention. My dear friends! I am sure this article will enhance your knowledge regarding diet and exercise required to cure cancer.

Dear friends! Hearing loss has many forms. The most common is related to the body aging process and to long term cumulative exposure of the ear to sound energy. As one grows older, it becomes more difficult to hear. The ear becomes less sensitive to sound, less precise as a sound analyzer and less effective as a speech processor. Loss of hearing differs greatly in different individuals. Changes in the ear occur gradually over time. However, by the time the changes are manifested, it is estimated that approximately 30 to 50 percent or more of the sensory cells in the inner ear have suffered irreparable structural damage or are missing.

Conventional Hearing Aid: Modern hearing aids have evolved from single-transistor amplifiers to modern multi-channel designs containing hundreds and even thousands of transistors. The basic functional parts include a microphone and associated preamplifier, an output transducer or receiver. The total circuitry works on a battery. The use of multiple channels in this design provides different compression characteristics for different frequency ranges. Typically, the crossover frequencies of the channels and the compression characteristics can be adjusted with potentiometers. The register outputs are used to switch resistor networks that control various analog circuits. The active filters are adjusted to generally provide for low-frequency attenuation. This is because most hearing aid wearers require high frequency gain.

Digital Hearing Aid: The major parts are the microphone, an analog-to-digital converter (ADC), the digital signal processor (DSP), the digital-to-analog converter (DAC), the receiver and a two port memory. Essentially, sound waves picked up by the microphone and transformed into electrical signals are converted into digital form by an analog to digital converter. A typical microphone will have an internal noise of 20 db sound pressure level when referred to the input and maximum undistorted output corresponding to a signal of about 90 db sound pressure level. Allowing some margin for peak performance, the total dynamic range required of the analog digital converter is 80 db. This requirement can be achieved with a 14 bit analog to digital converter. My dear friends! I am sure this article will enhance your knowledge regarding the digital and conventional hearing aids.

Dear friends! An important development in the field of defibrillators has been the development and successful use of smart automatic or advisory external defibrillators (AEDs) which are capable of accurately analyzing the ECG and of making reliable shock decisions. They are designed to detect ventricular fibrillation with sensitivity and specificity comparable to that of well trained paramedics, then deliver or recommend an appropriate high energy defibrillating shock.

AEDs require self-adhesive electrodes instead of hand-held paddles for two reasons. Firstly, the ECG signal required from self-adhesive electrodes usually contains less noise and higher quality; hence, it allows a faster and more accurate analysis of the ECG and, therefore, facilitates better shock decisions. Secondly, hands-off defibrillation is a safer procedure for the operator, especially if the operator has little or no training.

It was initially though that different self-adhesive electrode designs were needed for defibrillation, pacing, and monitoring. A critical factor in the safety and performance of an automatic external defibrillator is the ability device to accurately assess the patient’s heart and make an appropriate therapy decision. The defibrillator performs this evaluation by sensing electrical signals from the patient’s heart via electrodes and using a computerized algorithm to interpret the electrical signals. An automatic external defibrillator optimized for infrequent used by both first responders and untrained bystanders have been introduced by the agilient technologies, USA.

It is small, light, and virtually maintenance free while it is on standby for long periods, the device automatically self-tests its electronic circuitry everyday and periodically performs an internal discharge and recalibration. The device is powered by a long life disposable lithium battery. It uses a low energy biphasic waveform with dynamic compensation which accommodates a wide range of patient impedances. Multi function self-adhesive electrodes are now commonly used with defibrillator monitor pacer instruments. My dear friends! I am sure this article will enhance your knowledge regarding the smart automatic or advisory external defibrillators.