Glossary - healthcare electronics

Pressure sores have always been a problem for patients who are confined to bed for long periods of time. At the point on the patients body that makes contact with the mattress, a sore can develop that can ulcerate or become infected. It is inevitable that this would make the condition of the patient worse and slow down the recovery from first hospitalisation, as there is a secondary treatment needed. The patient must be regularly moved to a different position to alleviate the risk of a pressure sore. The idea of an Air bed is to reduce the need for turning as this is done to some degree automatically. The mattress is constructed of cells that are alternately inflated. This is done by a compressor with two outputs that alternate between each other. The compressor can sense a leak in the mattress and sound an alarm. There is a quick release C.P.R. plug to deflate the mattress in-case of an emergency where the patient needs to be resuscitated.

The ambulatory ECG recorder is the size of a personal stereo and is worn on a belt or strapped to the patient. It has electrodes that are attached to the chest and these pick up the ECG signal. This is then recorded onto the cassette tape which runs slow enough for 24 hours recording. The tape is then rapidly analysed by a machine that stops when it detects any abnormalities in the recording. The technician who controls the playback machine makes notes to report back to the physician. Also, there is a ambulatory blood pressure machine available that will make blood pressure recordings every five minutes and record 24 hours worth of data. In a similar way as the ECG recorder, this machine downloads the data to a PC that analyses the recording.

Integrated anesthesia delivery system, which includes the supply and control of anesthesia gas, a breathing and ventilation system, and a scavenging system for dispensing and delivering anesthetic gases and vapours into a breathing system.

Connected to the exhaust port(s) of an anaesthesia machine, this system conveys expired and/or excess anaesthesia gases to an appropriate place of discharge.

A medical device which is used to convert the anaesthetic agent from a liquid to a vapour.

Often for neonate or paediatric use, an apnoea monitor detects breathing with a strain gauge affixed to the chest to detect the expansion or with electrodes that measure the change in impedance as the chest moves. The device sounds an alarm if no breath is detected after a pre-set time. The alarm which is usually quite loud may actually startle the infant into breathing again. The audible alarm feature can often be switched off just to give a visual indication with flashing indicators. An apnoea alarm is ‘loaned’ to a parent of a child by the clinician that may suspect breathing difficulties. An apnoea alarm is also found in the operating theatre in conjunction with ventilators which would monitor the breathing of the unconscious patient. The alarm would alert the anaesthetist of a problem with the breathing circuit or patient.

A medical device instrument for evacuating fluid by suction. A common use of an aspirator is the tube-like straw which a dentist places into the patient’s mouth to evacuate the saliva.

An Autoclave is a pressure steam cleaners used to sterilise and decontaminate surgical equipment. The surgical instruments are usually wrapped in a porous material and sealed with indicating tape before being placed in the oven. The air inside the oven is evacuated before the high pressure steam is let in. Because the steam is under pressure it can get to a very high temperature that would be pre-set on the front panel. The steam contacts all parts of the instruments before the oven is then evacuated again. This action dries the instruments. The indicating tape that sealed the wrapping, changes colour to indicate that the process is complete and the instruments are sterilised ready for use.

Babies need to be kept warm because they cannot control their body temperature as adults can. These devices are often an overhead heater placed over the cot that contains an electrical heating element that is pre-set, or sometimes with a thermistor on the patients skin to control the thermostat. A warm water filled mattress is also used that can be placed in a cot that the baby is placed on.

Used in anaesthesia, this variant of a T-piece is a coaxial system in which fresh gas flows through a narrow inner tube within the outer corrugated tubing. The patient inspires fresh gas from the outer reservoir tube and expires into the reservoir tube. The fresh gas that is flowing into the system at the time of expiration is wasted as it is contaminated by expired gas, so there is an expiratory pause in which the fresh gas from the inner tube washes the expired gas out of the reservoir tube, filling it with fresh gas.

The branch of medicine which deals with the causes, prevention, and treatment of obesity, both pharmacological and surgical. Bariatric medical furniture, such as bariatric chairs and bariatric tables, are designed to accommodate the special needs of overweight or obese people.

An intestinal tube placed into the duodenum or jejunum for the performance of various gastrointestinal radiologic studies. The tube is placed with the aid of a stiffening guide wire.

BiPAP stands for Bi-level Positive Airway Pressure. It is a breathing apparatus that helps people get more air into their lungs. The development of BiPAP allowed air delivered through a mask to be set at one pressure for inhaling and another for exhaling. Because of these dual settings, BiPAP allows people to get more air in and out of the lungs without the natural muscular effort needed to do so.

Also known as diathermy, this is one of the two types of electrocautery. With this type, the active and receiving electrodes are both placed at the site of cauterisation. The probe is usually in the shape of a forceps with each tine forming one electrode, cauterising only the tissue between the electrodes. For information on the other type of electrocautery, see Monopolar Electrocautery.

Blood pressure is a measurement of the pressure inside the arteries as blood is pushed through the circulatory system. This pressure is highest when the venticles in the heart contract to push blood into the system (measured as the systolic reading, or the top number of blood pressure), and lowest when the venticles are relaxed (measured as the diastolic reading, or the bottom number of blood pressure). Both of these pressures are measured in millimetres of mercury. Normal blood pressure is 120/80.

Breast milk can be drawn from the mother for bottle feeding. A breast pump causes a low, adjustable suction and with the aid of a suction cup, the milk is drawn off and is placed into a container. The milk can then be used to feed the baby with the use of a bottle.

To check, adjust, or determine the graduations of a quantitative measuring instrument by comparison with a standard.

Determination, by measurement or comparison with a standard, of the correct value of each scale reading on a meter or other measuring instrument; or determination of the settings of a control device that correspond to particular values of voltage, current, frequency or other output.

The monitoring of the concentration of CO2 in the respiratory gases. Used as a monitoring tool for anaesthesia and in ICU.

A cautery machine used in a clinic is often an adjustable current output DC power supply with leads attached to a hand piece that holds a thin wire loop. As the current passes, the wire is heated rapidly. The heat of the wire is controlled by the adjustable current. The heat dissipated through the tissue causes coagulation and that can be used to stop bleeding or for cutting tissue. The wire loop is self sterilising as the heat passing through causes the wire to be at a very high temperature.

A mechanical medical equipment device which is used for spinning small mixed samples very rapidly. Using centrigual force, solid or liquid particles of different densities are separated by high-speed rotation. The particles are placed in a tube in a horizontal circle around a fixed axis, applying force perpendicular to the axis. The denser particles move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end. This has the same effect as filtration.

A CO2 (carbon dioxide) absorber is a device used during the administration of anaesthesia. The apparatus contains an absorbent material (such as soda lime), which is used to remove carbon dioxide from the gas exhaled by the patient.

CO2 monitoring is used during anaesthesia. Many potentially dangerous situations can be first detected using CO2 monitoring. The anaesthetic gas breathed by the patient is continuously sampled by the device that passes the sample past an infra-red light source. The absorption of the light is detected and the results are displayed in a wave form and percentage concentration. The wave form displayed clearly shows the breathing pattern of inhalation and exhalation. The first gas exhaled contains no CO2 because this gas has been in the dead space (the neck, mouth and face mask) and not in the alveoli therefore no gas exchange has taken place. Eventually, during exhalation, the gas is purely from the alveoli and this is measured as ‘end tidal CO2’ or ETCO2. On inspiration, the minimum level of CO2 is detected (0.0%) and this is the inspired CO2.

An apparatus for cooling a gas in order to convert it to a liquid or the simple or compound lens on a microscope that is used to focus light on the specimen under observation.

A Cryosurgery device uses a gas, typically CO2 that is fed from a pressure reducing regulator to a hand held pistol grip with a trigger. Attached to the hand piece is a metal tip. When the trigger is operated, the metal tip is rapidly taken to a very cold temperature, below freezing. Used in theatres, special clinics and chiropody, the metal tip is rapidly cooled on contact with the skin. The freezing action causes the tissue to die and the surrounding area is coagulated.

There is special equipment available to assist those who are deaf or hard of hearing. You may realise that many everyday items utilise an alarm or sound to warn you or catch your attention. Sound activated systems are devices that attach to telephones and doorbells and flash lights or use vibrating pagers to alert the user. There are unique devices such as smoke alarms to alert you if you are asleep and Baby alarms that operate vibrating pads, and that flash lights. Some telephones are hearing aid compatible, which means that you can switch your hearing aid to ‘t’ and the sound is amplified while background noise is cut. On some videos there are hidden captions that can be viewed when you use a special box to plug into your video. Contact : movietext@compuserve.com for more information.

A medical equipment device that is used to administer an electric shock to the heart in order to re-establish normal heart rhythm.

A defibrillator (defib) is used when the heart goes into fibrillation. This is when normal electrical activity of the heart is in a confused state and the heart is out of sync with itself. In fibrillation the heart is pumping ineffectively and is in more of a spasm. It was found that a ‘short sharp shock’ could bring the heart out of fibrillation and bring it back into its normal routine. Fibrillation could be caused by heart disease or an electric shock and can cause death within a few minutes. The fibrillation signal is a rapidly oscillating wavy trace that can be monitored using the ECG on the defib (through the paddles or separate ECG leads). A current is passed for a very short time through two paddles across the chest, and the patient's ECG signal is monitored and normal sinus rhythm is looked for.

Dental surgeries have many different types of equipment. Drill : The drill a dentist uses works from compressed air or an electric motor. The drill has a mandrel that takes different type of tools. Suction : The suction machine is used to remove debris from the mouth. Compressed air : Compressed air is used to look for cavities and sometime to remove debris. Light source : The light source is used to get a clear view of the mouth. Dental Chair : The dental chair has electric motors to enable the dentist to get the patient into the ideal position. The dental unit would also have anaesthetic machines for use in general surgery, along with oxygen and resuscitation equipment.

Small unwanted molecules can be removed from the patients blood if the kidneys have failed by the use of a Haemodialysis machine. Dialysis is the process whereby crystalloid and colloid substances are separated from a solution by interposing a semi-permeable membrane between the solution and pure water. The substances pass through the membrane until equilibrium is achieved. This is the principle upon which the artificial kidney works. When the patient's blood is used the process is known as Haemodialysis. When the dialysing fluid is passed into the abdominal cavity, and the peritoneum is used as the semi-permeable membrane, the process is known as Peritoneal Dialysis.

In the measurement of blood pressure, the bottom of the two blood pressure numbers refers to the diastolic measurement. The term refers to the period of time between two contactions in which the heart is at rest and the ventricles have relaxed.

Also known as bipolar electrocautery, this is one of the two types of electrocautery. With this type, the active and receiving electrodes are both placed at the site of cauterisation. The probe is usually in the shape of a forceps with each tine forming one electrode, cauterising only the tissue between the electrodes.

Johann Christian Doppler (1805-1853) first put forward the principle of the phenomena we now know today as the Doppler effect. The phenomena affects all waves when the source and receiver are moving relative to each other. Simply, a motor engine could be the source and your ear could the receiver. As the motor engine moves away from the ear, the note of the exhaust appears to go lower in tone. The shift in tone is the Doppler effect. The first measurement of blood flow in the heart was by Satomura in 1956. Bats use ultrasound to visualise their environment similar to the way echo cardiograph machines work to give images of the heart. The sound waves are pulsed into the Piezo crystals that project the sound. In between the pulses, the Piezo crystal is used to ‘listen’ for an echo. As the ultrasound penetrates tissue, the sound is absorbed or reflected. The strength of the echo depends on the density of the tissue. The results are displayed on a monitor where the intensity of the echo is shown in grey scales or colour. Alternatively, the results of the echo are amplified to a loudspeaker where one can hear the pulsations of blood flow or fetal heart.

This is equipment which can withstand repeated use, is primarily used to serve a medical purpose, is generally not useful to a person in the absence of an illness or injury, and is appropriate for use in the home.

Einthoven gave an alphabetical lettering to the ECG (electrocardiograph) wave form because he did not know the origins and did not wish to suggest interpretation by his labelling. Muscle cells are surrounded by a semi-permeable membrane which allows sodium ions to pass through. When the cell is at rest, there is a larger concentration of sodium ions outside the cell than are in it. You could measure about -90 mV across the membrane. When the cell is excited by a stimulus, the membrane begins to move sodium ions into the cell and the potential across the membrane would become less negative. The membrane has a threshold (about +40 mV) where it peaks, and starts to transport the sodium ions back out of the cell. Depolarisation is the act of going from -90 mV to +40 mV. During depolarisation, the muscle cell contracts. Repolarisation is where the membrane transports sodium ions back out of the cell. During repolarisation, the muscle cell relax. The basic ECG wave form represents a voltage level of the heart muscle, and consists of three recognisable deflections. The p wave , the QRS complex and the T wave. The depolarisation of the atria is represented by the ‘p’ wave, where the atria are contracting, forcing blood into the ventricles. ‘Q’ is the point where the ventricles begin depolarising and contracting. The time between ‘q’ and ‘s’ immediately precedes full contraction of the ventricles when blood is being forced into the arterial system. The ‘t’ wave represents the refractory period of the heart when the ventricles are depolarising.

First used by Berger (1924), an ELECTROENCEPHALOGRAPH (E.E.G.) is a machine that detects and records electrical activity in the brain. It does this by measuring potential differences (voltages) between electrodes placed on the scalp. The EEG machine may have up to sixteen channels that measure brain activity occurring as the result of ‘feeble currents’. The EEG signals are distinguished by their frequency and by the region of the head in which they arise. ALPHA WAVES (8 - 13 Hz) found in the occipital region are associated with relaxation and BETA WAVES (15 - 30 Hz) in the frontal region. Used in Neurology to diagnose disorders of the brain caused by epilepsy, and sometimes tumours, the machine requires skilled clinicians although the advent of computers have brought new machines that provide diagnosis for doctors.

The curve traced by an electrocardiograph.

Medium used between an electric conductor and the object to which the current is to be applied. In electrotherapy, electrodes are instruments with a point or surface from which to transmit electric current to the body of a patient or to another instrument; in electrodiagnosis, they are needles or metal plates used to stimulate or record the electrical activity of tissue.

The surgical use of high-frequency electric current for cutting or destroying tissue, as in cauterisation. Electrosurgery is performed using an electrosurgery unit / electrosurgical generator (also referred to as power supply or waveform generator) and a hand piece including one or several electrodes, sometimes referred to as an RF Knife. The apparatus when used for coagulation in surgery is still often referred to informally by surgeons as a 'Bovie', after the inventor.

Also referred to as a Power Supply or Waveform Generator. Medical equipment used during electrosurgery with a hand piece including one or several electrodes.

Acronym for Electrosurgical Generator, also known as an electrosurgical unit, or ESU. Medical equipment which powers an electrosurgical system with electricity at an appropriate voltage, frequency and waveform for cutting or for coagulation, as required.

Acronym for Electrosurgical Unit, also known as an electrosurgical generator, or ESG. This device powers an electrosurgical system with electricity at an appropriate voltage, frequency and waveform for cutting or for coagulation, as required.

Device used to measure the flow of fluids, or the air to measure respiration.

The heart lung machine replaces the function of the heart and lungs during surgery on these organs. The machine was first used by Gibbon in 1953 The machine circulates the patients blood through a special peristaltic pump, designed not to damage the cells in the blood. The blood is passed over a permeable membrane where a gas exchange takes place. Carbon Dioxide is removed from the blood and oxygen is absorbed by the blood. This gas exchange mimics lung function and the peristaltic pump replaces the heart.

A medical device used in open heart surgery to support the body during the surgical procedure while the heart is stopped. It is also referred to as a 'cardiopulmonary bypass pump' as it is used during cardiopulmonary bypass surgery. The heart-lung machine consists of a chamber that receives the blood from the body, which is normally the responsibility of the heart’s right atrium. This chamber temporarily holds the blood before it is diverted to an oxygenater and pumped back throughout the body.

A portable, wearable EKG device that is worn by the patient (usually for a period of 24-48 hours) to continuously monitor heart rhythms. The use of this device is especially effective in the diagnosis of rhythm problems, atrial fibrillation, angina, and other transient symptoms (those abnormalities which only appear sporadically and may not appear during a resting ECG).

A humidifier is used when the patient is anaesthetised or during ventilation to enrich the gases with water vapour because the gases used are too dry.

The definition of hyperbaric is 'at higher than normal pressure (esp. oxygen)'. Originally pressurised vessels were developed to combat decompression sickness suffered by deep sea divers. If a diver surfaces too quickly, molecules of nitrogen form into bubbles in the blood and cause the ‘bends’. This can be overcome by placing the patient in the chamber, increasing the pressure until the nitrogen is forced back into solution within the blood and then slowly reducing the pressure in a controlled way to stop the bubbles forming. This process is akin to opening a pop bottle too quickly and watching the carbon dioxide gas come out of solution. It was later discovered that an oxygen rich atmosphere within the vessel aided the application of oxygen therapy and accelerated the healing of wounds. Deep sea divers are sometimes transported from one dive site to another in hyperbaric chambers to avoid long inter dive decompression times.

A method of measuring blood pressure internally by using a sensitive IV catheter inserted into an artery. This provides a more accurate reading of the patent's current blood pressure.

Premature and under weight babies are placed inside heated incubators. Helping to control their body temperature saves vital energy giving them the greatest chance of survival because they need as much of their energy as possible to grow and fully develop. The incubator has an electrical heating element that is controlled by thermostats. There is a fan that circulates the heat to get an even distribution. The stabilised temperature is usually set to 37 ºC before the baby is put in. Most incubators incorporate oxygen controllers so that a specified oxygen concentration and humidification can be set. Incubators alarm at over/under temperature, fan fail, mains failure and oxygen over/under concentration.

Also known as a radiant warmer, an infant warmer is a medical apparatus that consists of an open bed with an overhead warmer which is used to keep an infant warm.

Infusion devices are mechanical pumps used to administer liquid drugs in-vitro from a fluid filled bag via a giving set. Flow rate and volume infused can be pre-set as can sometimes the maximum pressure in the line. Often, the infusion device has in-built sensors to detect air in the line and pressure sensors to stop the pump in the event of a blockage or occlusion. The most common form of infusion pump uses a peristaltic mechanism to drive the fluid through the line. A drop sensor connected to the device and attached to the drip bag counts the drops and checks for loss of flow or over infusion.

A device used to infuse fluids, medication or nutrients into a patient's circulatory system in a controlled manner. It is generally used intravenously, although subcutaneous, arterial and epidural infusions are occasionally used.

Also known as intravenous (or I.V.) therapy. Concerns the introduction of fluid other than blood into a vein.

Insufflators inflate the abdomen so that laparoscopes can move more easily around the organs. H. Fragenheim introduced a prototype automatic insufflator in the 1950's. A cannula is passed through the skin into the peritoneum and is connected to the Insufflator. The inflation is called a 'pneumoperitoneum', carbon dioxide being the most common gas used. The gas flow is controlled between 1 Lt /min and 10 Lt /min at a pressure of approximately 15 mmHg

A device used to treat medically by blowing a powder, gas, or vapour into a bodily cavity.

A medical device that uses a balloon catheter which is used to augment the functioning of a severely weakened heart. The catheter is placed in the aorta and is inflated and deflated in synchronisation with the patient’s heartbeat.

The Iron Lung was used in the treatment of respiratory disease, paralysis and in anaesthesia but most extensively during the poliomyelitis epidemics of the 1930’s and 1950’s. The Iron lung is a device that provides artificial respiration by mechanical means. Negative pressure units are a sealed vessel containing the patients body with the head protruding and a seal around the neck. The rhythmic removal of the air from the vessel forces the patient to take in air through the nose and mouth. Positive pressure units (ventilators) force air into the lungs through a close fitting tube into the trachea.

More commonly referred to as an incubator. See 'incubator' for additional information.

A type of medical insufflator which is inserted through a small incision in the abdomen during an investigative surgical procedure. This device is used to maintain constant intra-abdominal pressure in the patient. Some types of laparoflators include a heating system to prevent lowering the patient’s body temperature.

A cosmetic surgery procedure that removes fat from many different areas of the human body. Liposuction can remove fat from the abdomen, neck, thighs, buttocks, arms, and more.

The clinician needs to have accurate measures of the patients lungs to aid the observation or diagnosis of pulmonary problems. Accurate measures of lung capacity and forced flow are taken and compared to predicted values. The patients age and height are taken into account before the results are compared to statistics.

The equipment in use in maternity departments is primarily aimed at the baby, although there are breast pumps, thermometers, oxygen therapy, and patient weighing scales used on the mother. Other equipment may include an incubator, overhead heater, heated cots,

Also known as monothermy, one of the two types of electrocautery. Electrical current is passed from the probe (active electrode) where cauterisation occurs and the patient's body serves as a ground. A grounding pad (returning electrode) is placed on the person's body, usually the thigh, and it carries the current back to the machine. Careful application of the return electrode is necessary as extensive burns can occur undetected if the electrode is not correctly positioned. For a definition of the other type of electrocautery, see also Bipolar Electrocautery.

Also known as monopolar electrocautery, one of the two types of electrocautery. With this type, electrical current is passed from the probe (active electrode) where cauterisation occurs and the patient's body serves as a ground. A grounding pad (returning electrode) is placed on the person's body, usually the thigh, and it carries the current back to the machine. Careful application of the return electrode is necessary as extensive burns can occur undetected if the electrode is not correctly positioned. For a definition of the other type of electrocautery, see also Bipolar Electrocautery.

A medical device used to deliver oxygen at low flow rates to a patient or person in need of extra oxygen. This device, which is connected to an oxygen tank or portable oxygen generator, consists of a plastic tube with two plastic prongs that are inserted into the nostrils of an individual, allowing oxygen to flow from the oxygen source, through the tubing and out through the prongs into the individual’s nose.

Used in the treatment of certain respiratory ailments, a nebuliser is a machine that converts the liquid medication into a fine mist that the patient can inhale. Nebulisers are air compressors that are powered from mains and give an output of about 15 p.s.i. at a flow rate of about 2 litres per minute. Tubing is attached to the output of the compressor and the other has a chamber that holds the fluid drug and a face mask. The pressure from the nebuliser forces the drug through a small hole that creates a mist that the patient breathes in. The aerosol mist that is breathed ensures that the drug is administered direct. They have a filter on the air intake that should be regularly replaced.

Body ventilators that assist ventilation by applying intermittent subatmospheric pressure around the thorax, abdomen or airway and periodically expand the chest wall and inflate the lungs, including the tank ventilator, Portalung, Pneumowrap, and chest cuirass.

NIBP is a commonly-used acronym for Non-Invasive Blood Pressure, used to describe oscillometric blood pressure monitoring.This oscillometric equipment uses an electronic pressure sensor (a calibrated electronic device with a numerical readout of blood pressure) to detect blood flow, instead of relying on the stethoscope and ear as is used in the traditional auscultatory method.

Commonly referred to by the acronym NIBP, Non-Invasive Blood Pressure, is a term used to describe oscillometric blood pressure monitoring.This oscillometric equipment uses an electronic pressure sensor (a calibrated electronic device with a numerical readout of blood pressure) to detect blood flow, instead of relying on the stethoscope and ear as is used in the traditional auscultatory method.

An anaesthesia breathing circuit that incudes a reservoir bag, wide-bore corrugated tubing, and a spring-loaded expiratory valve. This system is semi-closed to prevent rebreathing by having the gas flow rate from the cylinders slightly in excess of the patient's minute respiratory volume.

System from where all the expired mixtures of gases are directly discharged.

One of the first requirements of a physician is to be able to see the cause of the patients problem. Originally doctors used natural light and a head worn reflector.

Commonly known as Non-Invasive Blood Pressure (NIBP).This oscillometric equipment uses an electronic pressure sensor (a calibrated electronic device with a numerical readout of blood pressure) to detect blood flow, instead of relying on the stethoscope and ear as is used in the traditional auscultatory method.

A device that monitors the amount of oxygen carried by the haemoglobin in red blood cells. In bloodless medicine, any blood a patient loses is not replaced by transfusion, so it is extremely important to monitor how much oxygen the patient's body is receiving from the remaining blood.

A device used to provide oxygen therapy to a patient at substantially higher concentrations than available in ambient air.

A medical equipment device that provides continuous oxygen monitoring for anaesthesia delivery equipment, as well as hospital and home ventilators.

Any of several usually miniaturised and surgically implanted electronic devices used to stimulate or regulate contractions of the heart muscle.

Medical equipment consisting of microphones and recording equipment used to monitor and record heart sounds and murmurs.

A catheter with a miniature microphone in its tip used in recording sounds and murmurs from within the heart and large blood vessels.

Physiotherapy equipment is many and varied. Heat is a common treatment often used in the form of hot wax, and more physical treatments include traction. Electrotherapy is used to treat muscle pain and strains in the form of interferential. This is a differential treatment that produces two independent sets of stimulating currents at different frequencies that can be pre-set. Each set of skin electrodes are placed at opposite sides of the affected area. Where the stimulating currents cross over, there is an interference that produces the treatment region. Ultrasound is used to generate heat in the body that can be applied to the affected area to treat pain, injury and inflammation.

Carl Matthes (USA) in 1935 built the first machine to measure human blood oxygen saturation, and in 1951 a paper was published that declared oximeters were capable of detecting low oxygen saturation levels before any clinical evidence of cyanosis. Hewlett-Packard invented an ear oximeter in 1970 but it was in 1974 that Takuo Aoyagi discovered pulsation's in the signal. Scott Wilber produced a sensor with cable to connect it to the instrument, and he recorded human volunteer data to improve the reliability of saturation estimates. It is from such statistics that modern pulse oximeters give their results, as they use empirical values in a ‘look-up table’ with a microprocessor. Oxygen is carried by the blood to tissue where it is required. Oxygen is carried mainly by a protein called haemoglobin. One molecule of haemoglobin can carry up to four molecules of oxygen which would then be 100% saturated, and therefore a pulse oximeter measures the oxygen saturation of haemoglobin in arterial blood. A pulse oximeter shines two different wavelengths of light through a finger or ear lobe. Some of the light is absorbed by tissue depending on the level of oxygenated haemoglobin. A photo detector sends the signal to the microprocessor which determines how much oxygen is saturated in the blood. The device also measures the pulse rate which is displayed along with the oxygen saturation and the wave form of the signal.

Also known as an infant warmer, a radiant warmer is a medical apparatus that consists of an open bed with an overhead warmer which is used to keep an infant warm.

Breathing circuits used during the administration of anaesthesia in which the exhaled gas is re-circulated to the patient with CO2 removed.

The number of breaths (inspirations and expirations) in one minute.

In any emergency, resuscitation equipment needs to be close to hand. Equipment may include oxygen, suction, a portable ventilator, or a defibrillator.

Also known as a lymphedema pump, this medical device is designed to limit the development of Peripheral Edema and Deep Vein Thrombosis (DVT) in immobile patients. This device consists of an air pump which is connected to a disposable sleeve by a series of air tubes. The sleeve is placed around the patient’s leg and air is forced into different parts of the sleeve in sequence, creating pressure around the calves and improving venous return. This is done to combat the tendency of blood pooling in the calf area of the lower leg when a patient is immobile for long periods of time. It is used to treat various medical conditions such as lymphedma, leg ulcers, and lymphostatic disorders.

Ophthalmologists started examining eyes by using hand held loupe's. The mounted microscope and head cradle replaced this and later the slit lamp was added. Slit lamp microscopy was pioneered by Alfred Vogts. His descriptions and observations were seen at the time as the definitive study of the eye. A slit lamp is used to look for foreign bodies or defects in the eye. Improvements in optical design and image analysis have taken this instrument much further although the basic design remains. A chin rest holds the head still and an adjustable beam of light shines into the eye while the clinician looks through the magnified image.

A sound level meter can be used to measure levels of ambient noise from conversations in specified areas.

A medical device, also known as a blood pressure meter, that comprises an inflatable cuff to restrict blood flow and a mercury or mechanical manometer to measure the individual’s blood pressure.

A medical device that tests lung function by measuring lung air volumes and flow rates.

A measurement of the saturation level of oxygen in the haemoglobin. Normally, this measurement is determined with the use of pulse oximetry, a non-invasive procedure.

An acoustic medical device used to transmit low-volume sounds such as heatbeat or intestinal, venous, or fetal sounds. This instrument generally comprises two earpieces that are connected by means of flexible tubing to a diaphragm, which is placed against the skin of the patient.

In some cases of heart disease, one way to carry out investigations is to put the heart under some stress. This is usually done by having the patient walk on a gradient-adjustable treadmill, which will be controlled by a computer. The patient will be connected to an ECG recorder. The test, of which there are several profiles, will then slowly increase the gradient of the treadmill to make the heart work a little harder. The computer monitors the patient, making sure it doesn't push the patient too far, and records the stress versus heart response. From this data the clinicians can decide on the required treatment.

Suction machines are powered from mains or sometimes from battery. An electric motor drives a mechanical pump that creates an adjustable suction usually of maximum -700 mmHg They are used with catheters for drainage purposes from oral (in the case of resuscitation) or surgical sites during operations.

Once a syringe has been filled with a drug, it can be mounted onto a syringe driver that will inject the drug at the rate that the clinician sets. Some syringe drivers automatically detect the size of syringe and ask the user to confirm the syringe size. Others, you must use the correct size syringe. Then the user must set the flow rate. Also the volume to be infused can be set. The syringe driver will detect an occlusion (a blockage), stop and alarm. Most syringe drivers have internal rechargeable batteries so that the patient can move if needed and the device will still work.

In the measurement of blood pressure, the top number refers to the systolic measurement. Systolic is a measurement of the maximum blood pressure reached as the blood is pumped out of the heart.

Medical equipment which monitors the remote measurement and transmission of patient data via a telecommunications system to a provider's site for analysis and decision making.

Transcutaneous electronic nerve stimulators (Tens) are used to treat pain or injury. The device is powered with a battery and electrode pads are placed on the skin. The machine gives an output that can be preset, of pulsed electrical stimulation of varying degrees of intensity and frequency. The concept of electrical stimulation for pain relief is far from modern. The first recorded use was some 2000 years ago, by the Roman Physician, Scribonius Largus. He applied electric eels to haemorrhoids, arthritis, headaches and gout sufferers. Although there is some evidence of electrotherapy in the Middle Ages, it was not until the early 19th century that the next recorded details appear. Duchenne De Boulogne developed the earliest forerunner to the TNS machine in the mid 1830’s, using cloth covered electrodes on the skin over the points of entry of the muscular nerves. Faraday developed the electromagnetic generator producing alternating current in 1831. This lead to excessive charlatanism and Electro-Quackery, including claims to cure not only pain, but such problems as poisoning and sexual impotence. By the 20th century continued advances in the field resulted in such developments as the cardiac pacemaker. TNS was introduced into clinical practice following Malzark & Wall's 'Gate control theory'.The TNS machines are usually battery powered with 1 or 2 sets of electrodes. The electrodes are positioned over the path of a peripheral nerve innervating the painful area. For pain relief, the stimulation should be increased until it can be accepted, without being uncomfortable, the recipient should experience paresthesia at the site of the pain.

Two temperature scales are available in modern thermometers in hospitals, Celsius (formerly centigrade) named after Anders Celsius and Fahrenheit developed by Gabriel Daniel Fahrenheit. Celcius is more commonly used. Thermometers using a mercury column are slowly being phased out because of the toxic content in favour of electronic units that give quick and reliable results. The electronic thermometer has a probe which is placed in a disposable cover and placed in the mouth or under arm. The probe contains a thermocouple whose resistance changes proportional to heat applied. This resistance is measured by the unit and the result displayed digitally. Some electronic thermometers have anti-theft devices built in that alarm when the unit is removed from the building.

Humidification and medication of air or anaesthetic gases may be achieved by using high-intensity ultrasound to break up water, or sterilising agents, into tiny droplets. There are two main types, those in which the ultrasonic transducer is immersed in fluid from which the mist is projected, and those in which the liquid falls on to the transducer one drop at a time. Such devices are found in the wards and in the intensive care department. The unit may also incorporate a fan to assist the flow of gases which are being humidified.

A device for measuring and electrically recording the volume and rate of urine output from a patient in intensive care, via a urethral catheter. One such device senses the pressure head developed at the bottom of a narrow vessel. The vessel empties periodically and a computer record is made of the volumes emptied.

Originally problems were assessed by simple timed observations of fluctuations in collecting tubes fed from indwelling catheters. More recent advances have allowed machines to be developed that can carry out a host of investigations. Uroflowmeters actually plot the flow and volume of urine against time. The data is collected via the weight of urine voided, by dipstick capacitive measurement, depth / pressure measurement or current analysis of a spinning disc onto which urine is voided. Urodynamic Systems offer a complex series of tests that can show urethral pressures, bladder function, muscle tone and flow / volume data. They also profile peak flow, flow instability and can carry out fluid filled cystometry tests.

Medical equipment that produces vapour from volatile anaesthetic agents such as ether, chloroform, or halothane. Gases are blown through, over the surface, or over a wick of the volatile liquids to produce vapour.Vaporisers usually fit on the back of the anaesthetic machine so that the gas mixtures from the flowmeters can pass through, collecting the vapour.

A ventilator is a breathing machine used in anaesthesia, intensive care, and for emergency resuscitation. Often powered by compressed gas, ventilators force the patient to breath or assist in breathing to an adjustable preset pattern. Inspiration and Expiration times can be independently set, as can Cpap (constant positive airway pressure), PEEP (peak expiratory end pressure), and tidal volume. In-built alarms monitor conditions and are triggered by loss of pressure.

Medical equipment or a breathing machine for providing assisted or artificial ventilation of the lungs. It can thus mean a resuscitator for emergency use, a body respirator, or lung ventilator. In any form its function is to assist or take over from the spontaneous respiratory effort of the patient. These are used during anaesthesia, in intensive care for life support, and during emergency resuscitation.

Vital signs machines consist of Blood pressure, ECG, pulse oximetry, and temperature measurement. These devices are often very portable, being mounted on stands. The compactness of these machines is ideal as there is no need for several different pieces of equipment. The blood pressure measurement is non-invasive and measured with an inflatable cuff (usually around the arm), the ECG is measured from electrodes placed on the chest and the pulse oximeter measured with a finger probe. The vital signs monitor would be microprocessor controlled with a digital display showing all results of measurements and often have an in-built printer. Also there would be battery back-up to make the unit fully portable.

A bacterial filter for use in anaesthetic and lung ventilator airways.

A paper chart recorder for producing graphs of one variable against another. It has a separate signal amplifier to drive the pen in the X (horizontal) direction and the Y (vertical) direction. Such recorders are used in the audiology department for plotting acoustic impedance change against outer ear pressure, and for other applications to plot one variable against another.