Biomedical Instrumentation

Archive for the ‘Biomedical Safety’ Category

A range of electrical safety analyzers are commercially available for testing both medical facility power systems and medical equipment. They vary in complexity from simple volt-ohm-meter to computerized automatic measurement systems that generate hard copies of test results. The facilities available in these testers are given below.

Mechanical testing of electrical outlets: The power delivery point in the patient area usually consists of the outlets in the vicinity of the patient. The outlets should have three-prong wall receptacles that meet the ground retention force requirements as per the relevant standards. These force requirements are important as they ensure that plugs on medical devices do not fall out of the receptacle, possible placing the patient in danger.

Electrical testing of electrical outlets: Electrical testing of a wall receptacle should be made to determine whether power is available at the receptacle and if its polarity is correct. Proper polarity of the receptacles means that the hot, neutral and ground wires are connected to their correct positions. Miswiring of an outlet can happen during the original construction of the area or when broken outlet is replaced.

Patient safety: Hospitals are confronted with the difficult problem of creating a safe electric environment for the care and comfort of the patients. Electric shocks, burns and fire hazards result from the careless use of electricity. When electricity is relied upon to support life with devices like external pacemakers, respirators, and etc power failure is a continuous threat. Shock resulting from electric power is a common experience. Disruption of physiologic function by leakage current applied internally remains sometimes hidden and mysterious. Electric current can flow through the human body either accidentally or intentionally.

Electrical currents are administered intentionally in the following cases such as high frequency currents are also passed through the body for therapeutic and surgical purposes and also when recording signals like ECG and EEG, the amplifiers used in the preamplifier stage may deliver small currents themselves to the patient. Accidental transmission of electrical current can take place because of a defect in the equipment; excessive leakage currents due to defect in design; operational error and simultaneous use of other equipment on the patient which may produce potentials on the patient circuit.

To understand the process of intoxication, one must get a basic understanding of how drugs affect the brain. Certain parts of the brain govern specific functions of the body. For example the cerebellum is involved with coordination and the hippocampus with memory. Each section of the brain communicates with other sections as well as with the rest of the body, through brain cells called neurons. The human brain consists of billions of these neurons. Neurons send and receive messages through a combination of electrical and chemical impulses. This process in the brain is known as neurotransmission.

Neurotransmission involves chemical substances found in the neurons called neurotransmitters. There are a variety of known neurotransmitters in the human brain. One neurotransmitter that appears to be particularly important during drug intoxication is dopamine. Dopamine will be used to explain the process of neurotransmission. In the normal communication process among neurons, an electrical impulse travels down a neuron and causes it to release dopamine from storage vessels, located inside the neuron, known as vesicles. The dopamine is released into a small gap between neurons called a synapse.

The released dopamine binds with specialized proteins called dopamine receptors on a neighboring neuron, causing a new electrical impulse to occur. After the impulse occurs, the dopamine is released from the receptors and, within milliseconds, transported back to the storage site by the dopamine transporter. Drugs of abuse are able to interface with this normal communication process in the brain by mimicking the neurotransmitters. Cocaine, for example, mimics dopamine. After cocaine is consumed, it blocks the dopamine transporters from working normally. This results in a buildup of dopamine in the synapse.

In turn, this causes a continuous stimulation of the receiving neurons, causing the feelings of euphoria. Mood altering substances appear to affect neurotransmission in a particular area of the brain known to be associated with feelings of reward or pleasure. This reward area is also activated by other pleasurable activities, such as sex or eating. This section of the brain is actually a connected pathway comprising three separate areas: the ventral tegmental area, the nucleus accumbens, and the prefrontal cortex. When activated by a rewarding stimulus the information travels from the ventral tegmental area to the nucleus accumbens and the n up to the prefrontal cortex.

Transmission of medical images: One of the most important aspects of telemedicine is the acquisition and transmission of medical images such as X-rays, CT, MRI, histopathology slides, etc. These images used in telemedicine include:

• Images stored on traditional film or print media and converted into digital format by direct imaging or scanning in a raster sequence under controlled lighting conditions. Charge coupled devices and laser based scanners are commercially available for digitizing the film recorded X-ray images.
• Computer generated images available in standard video format, computer format, or computer file format. In modern digital radiography systems, the X-ray image is stored in the computer in the digital format. Being a film less system, it does not require any further digitization.

The American College of Radiologists and the National Electrical Manufacturers Association jointly developed a 13 part Digital Imaging and Communications in Medicine standard for the interconnection of medical imaging devices, particularly for radiological imaging equipment such as digital radiography, CT, MRI and PACS. At transmitting end, there is usually a requirement for the local storage of image data, particularly when the storage and forward concept is adopted in the telemedicine system. The number of images that may be stored depends upon the size of the storage facility and the amount of data compression applied to the images before the storage.

Transmission of video images: Telemedicine applications generally require video and individual still frame images for interactive visual communication and medical diagnosis. National Television System Committee adopted the signal format used in USA for the broadcast and cable transmission of television. Images are obtained from direct visualization by a video camera and a lens system for direct observation or an optical adapter to a conventional scope that provides magnification or remote access using fiber optics. Video is captured one frame at a time typically in a 640 by 480 pixel format, with an intensity scale typically consisting of eight bits for monochrome and 24 bits for color.

It is a common experience that hazards due to electric shock are also associated with equipment other than that used in hospitals. However, the equipments used in medical practice have to operate in special environments, which differ in certain respects from the others. Some such special situations are as follows:

• A patient may not be usually able to react in the normal way. He is ill, unconscious, anesthetized or strapped on the operating table. He may not be able to withdraw himself from the electrified object, when feeling a tingling in his skin, before any danger of electrocution occurs.
• The patient or the operator may not realize that a potential hazard exists. This is because potential differences are small and high frequency and ionizing radiations are not directly indicated.
• A considerable natural protection and barrier to electric current is provided by human skin. In certain applications of electro medical equipment, the natural resistance of the skin may be by- passed. Such situations arise when the tests are carried out on the subject with a catheter in his heart or on large blood vessels.
• Electrochemical equipment, e.g. pacemakers may be used either temporarily or permanently to support or replace functions of some organs of the human body. An interruption in the power supply or failure of the equipment may give rise to hazards, which may cause permanent failure of the equipment ma give rise to hazards, which may cause permanent injuries or may even prove fatal for the patient.
• Medical instruments are quite often used in conjunction with several other instruments and equipment. These combinations are often adhoc. Several times there are combinations of high power equipment and extremely sensitive low signal equipment and extremely sensitive low signal equipment. Each of these devices may be safe in it, but can become dangerous when used in conjunction with others.

The various factors listed above indicate that the electro medical equipment may be used in different places and under different circumstances. It is also obvious that an optimum level of safety can also be achieved when efforts are made to include safety measures in the equipment, in the installation as well as in the application.

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.