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Glossary

  • Aerospace Medicine: The field of preventive or occupational medicine concerned with the maintenance of health, safety, and performance of those involved in aviation and space travel. Aerospace medicine is the sum of aviation medicine and space medicine – health in flight both inside and outside the Earth’s atmosphere.
  • Aviation Medicine: This is the study of the biological and psychological effects of aviation. Medically significant aspects of aviation travel include exposure to changing temperatures, large inertial forces, oxygen deprivation, and air sickness, as well as pilot fatigue. Aviation medicine is also concerned, for instance, with the spread of disease by air travel and the adverse effects of noise and air pollution.
  • Space Medicine: This is the study of the biological and psychological effects of space travel. Medically significant aspects of space travel include weightlessness, strong inertial forces during liftoff and reentry, radiation exposure, absence of the day and night, and existence in a closed environment. Space medicine is concerned, for instance, with osteoporosis caused by weightlessness and the resultant increased risk of fractures. [Source: Medterm.com]
  • Accident: An unanticipated event, which damages the system and/or the individual or affects the accomplishment of the system mission or the individual’s task [Source: Sanders MS, McCormick EJ].
  • Acuity : It is the ability to discriminate at varying distances. An individual with an acuity of 20/20 vision should be able to see at 20 feet that which the so-called normal person is capable of seeing at this range
  • Aero Odontalgia: The pain experienced in teeth due to the expansion of gas pockets in and around the teeth as a result of poor fillings or from dental abscess formation at the apex of the tooth. The gas expansion can be caused by ascent to altitude.
  • Alveoli: The final division in the lungs; very fine sac-like structures where blood in the alveolar capillaries is brought into very close proximity with oxygen molecules. Under the effect of a pressure gradient, oxygen diffuses across the capillary membrane from the alveolar sac into the blood.
  • Anaemia: This occurs when cells of the various tissues are deprived of oxygen through insufficient haemoglobin or red blood cells.
  • Anthropometry: The study of human measurement.
  • Anxiety: A state of apprehension, tension and worry. It can also be a vague feeling of danger and foreboding.
  • Arousal: The measure of the Human Being’s readiness to respond. It can be said to be the general activation of the physiological systems.
  • Attention : Attention is the deliberate devotion of the cognitive resources to a specific item.
  • Auto-kinesis: This occurs in the dark when a static light may appear to move after being stared at for several seconds.
  • Autonomic nervous system (ANS): The nervous system controlling many of the functions essential to life, such as respiration, Arterial pressure gastrointestinal motility, urinary output, sweating, body temperature and the General Adaption Syndrome (sometimes known as the Fight or Flight Response) over which we normally have no conscious control.
  • Bacchus: The Roman God of wine and intoxication, equated with the Greek God Dionysus.
  • Barotrauma: Pain caused by the expansion and contraction, due to outside pressure changes of air trapped in the cavities of the body, notably within the intestines, middle ear, sinuses or teeth. Barotrauma can cause discomfort or extreme pain sufficient to interfere with the operation of the aircraft.
  • Bends: Experienced during decompression sickness when nitrogen bubbles affect the joints causing pain.
  • Blind Spot: The site on the retina where the optic nerve enters the eyeball. Having no light sensitive cells in this area, any image on this section of the retina will not be detected.
  • Blood Pressure: Blood pressure as measured in mm Hg at a medical examination is given as two figures eg 120/80. The first (highest) figure is the systolic pressure which is the pressure at systole when the left ventricle is contracting to send the oxygenated blood around the body to the various tissues. The lower figure is the diastolic pressure which is the constant pressure in the system even when the heart is not contracting.
  • Capillary: The smallest division of the blood circulation system. They are very thin walled blood vessels in which oxygen is in close proximity to the tissues and unlatches from haemoglobin. The oxygen molecules diffuse down a pressure dependant gradient across the cell walls into the respiring tissues. Carbon dioxide and water is picked up in exchange, and the capillary blood passes on into the veins.
  • Cardiac Arrest: State in which the heart ceases to pump blood around the body.
  • Central Vision: Vision at the Fovea. Only at this part of the retina is vision 20/20 or 6/6.
  • Chokes: The difficulty in breathing experienced as a result of decompression sickness.
  • Ciliary muscles: The ciliary muscles push and pull the lens of the eye to achieve the final focussing. – see also accommodation above.
  • Circadian Rhythms: Many physiological processes in the body exhibit regular rhythmic fluctuations, and they occur whether one is asleep or is kept awake. These rhythms are controlled not by reactions to the external environment but internally. The most common rhythms exhibited by man and other organisms have periodicities of, or about, 24 hours. These rhythms are termed “circadian rhythms”, from the Latin “circa” – about and “dies”‘ – day.
  • Cones: Light sensitive cells situated on the retina at the back of the eye which are sensitive to colour.. These cells convert light into nerve impulses that travel up the optic nerve to the brain where the visual picture is built up.
  • Coriolis : An illusion of a change in the turn rate due to a sudden movement of the head.
  • Cornea : A transparent focussing layer at the front of the eyeball.
  • Cyanosis : The development of a blue colour in those parts of the body in which the blood supply is close to the surface, the lips or under the fingernails, caused by a lack of oxygen in the blood and a consequent shortage of oxy-hemoglobin. Cyanosis is one of the signs of Hypoxia.
  • Diaphragm: A muscular and tendinous sheet separating the thorax and abdomen. Movement of the diaphragm helps to reduce the pressure in the chest, drawing air into the lungs. In the process of breathing out the diaphragm is relaxed.
  • Diffusion: The movement of particles from regions of high concentration to regions of lower concentrations.
  • ECG: Electrocardiogram, a device for measuring the synchronization of the brain’s electrical impulses with the beating of the heart (pulse rate).
  • EEG: Electroencephalogram, a device to measure the electrical activity of the brain.
  • EMG: Electromyogram, used to measure the electrical activity associated with the contraction and relaxation of muscles.Endolymph: The fluid which fills the inner ear and in particular the three semi-circular canals which are used to detect angular movement and provide balance cues for the brain.
  • Electrolytes : Electrolyte is a chemical capable of carrying or conducting an electrical charge in solution. The body relies on the presence of electrolytes to carry nerve impulses and to maintain cell metabolism.
  • EOG: Electroculogram, a device to measure eye movement using electrodes attached to the outer comers of the eyes.Episodic Memory: A part of Long-term memory storing episodes/events in our lives.Ergonomics: The principle of design which ensures that the job required should be fitted to the man rather than the man to the job
  • FDTL (Flight and Duty Time Limitation): Regulator defined duty schedule for a flight crewmember, to be mandatorily implemented by operators, where no flight crewmember may serve, in excess of the flight time or duty period limitations set forth in the regulation for flight duty time, including flight time, without a rest period.
  • Fovea: That part of the retina, composed only of cones, which is the most central part of the retina, only at the fovea is there 6/6 or 20/20 vision. It is the area of highest visual acuity and away from the fovea the acuity declines rapidly.
  • ‘G’: A useful concept in aviation, which is a ratio between a given acceleration and the acceleration due to gravity. The term ‘G’ force is used sometimes to describe a force, resulting in acceleration, which is a multiple of the acceleration due to gravity (9.81 m/sec2). Thus, an acceleration of 98.1 m/sec2 would be 10 G. In other words, say a combat pilot wearing a helmet weighing 1.5 Kg, while manoeuvring his aircraft at 5 G, shall have the helmet weighing five times, i.e. 7.5Kg, during that 5G manoeuvre.
  • Glaucoma : A disease of the eye which causes a pressure rise of the liquid within the eye. Glaucoma can cause severe pain and even blindness. Glaucoma exists in two forms: Acute and Chronic.
  • Haemoglobin: Haemoglobin is made up of a combination of protein and a chemical called Heme which has an atom of iron contained in the middle of the molecule. It is found in the red blood cells and has the property of uniting with oxygen in a reversible manner to form oxy-haemoglobin. The combination will release the oxygen again to a gas mixture which contains little, or no, oxygen. Haemoglobin has a much greater affinity for CO (carbon monoxide) than for oxygen, therefore the presence of carbon monoxide in the air will cause a reduction in the amount of oxygen that may be carried in the blood.
  • Hearing Loss: Caused by a number of factors. A breakdown of the eardrum / ossicles system is Conductive Deafness. The loss of some hearing as the natural consequence of growing old is known as Presbycusis. Hearing loss caused by damage to the sensitive membrane in the cochlea by the intensity and duration of loud noises is called “Noise Induced Hearing Loss”(NIHL).
  • Heart Attack: Also known as myocardial infarction. The blockage of one of the coronary arteries, usually by a clot, will deprive some of the heart muscle of an oxygen supply. The effects are dramatic, often with severe chest pain, collapse, and sometimes complete cessation of the heart. (See also Infarct)
  • Homeostasis : The process of the body maintaining physiological equilibrium through organs and internal control mechanisms in spite of varying external conditions.
  • Human Error: An inappropriate or undesirable human decision or behaviour that reduces, or has the potential for reducing effectiveness, safety or system performance [Source: Sanders MS, McCormick EJ].
  • Human Performance: a person’s ability to optimally use his or her capabilities.
  • Hypertension: High blood pressure.
  • Hyperventilation: Over-breathing, causing changes in the acid /base balance of the body. Can be caused not only by I lypoxia but also by anxiety, motion sickness, vibration, heat, high “G” or shock.
  • Hypoglycemia: Low sugar content of the blood normally caused by fasting not eating regularly.
  • Hypovigilance : Sleep patterns showing on an EEG during human activity.
  • Hypoxia:  Lack of Oxygen in the tissues due to decreased quantity and molecular concentration. In aviation, it occurs due to fall in partial pressure of oxygen in the inspired air with increasing altitudes.
  • Iconic memory: The visual sensory store. Physical stimuli which are received by the sensory receptors (eg eyes, ears etc) can be stored for a brief period of time after the input has ceased. The iconic memory only lasts for about 0.5 to one second but it does enable us to retain information for a brief period of time until we have sufficient spare processing capacity to deal with the new input.
  • Indifferent Zone Altitude : Sea level to 3,000m since ordinary daytime vision is unaffected. However there is a slight impairment of night vision.
  • Infarct: (Infarction). The death of a portion of a tissue or organ due to the failure of the blood supply. Hence the death of part of the heart muscle due to a failure of some of the coronary artery supply is also known as a “coronary infarction”.
  • Leans: Experienced when the vestibular apparatus of the ear has given an incorrect assessment of attitude leading to the senses of the pilot giving, for example, a “banking sensation” when the visual picture will tell him that he is “straight and level”.
  • Maximal Voluntary Contraction (MVC): Maximal holding time of muscles in sustained isometric contraction.
  • Mesopic Vision: Vision through the functioning of both the Rods and Cones.
  • Metabolism: The chemical processes in a living organism producing energy and growth.
  • Microsleeps: Very short periods of sleep lasting from a fraction of second to two to three seconds.
  • Myopia: Short sightedness. A longer than normal eye results in image forming in front of the retina. If accommodation cannot overcome this then distant objects will be out of focus.
  • NIHL: See Hearing loss.
  • Oculogravic Illusion : Visually apparent movement of a forward object that is actually in a fixed position relative to the observer due to the displacement of the Otoliths.
  • Oculogyral Illusion : A false sensation of movement of an object viewed by a pilot. It is the visual sister to the Somatogyral Illusion.
  • Orthodox sleep : Another term for slow wave sleep.
  • Ossicles: The small bones in the middle ear which transmit the vibration of the eardrum to the cochlea of the inner ear.
  • Otoliths: Literally “stones in the ear”. They are fleshy organs surmounted by calcite crystals located at the base of the semicircular canals and act as linear accclerometers.
  • Paradoxical Sleep: Another term for REM Sleep for although the person is certainly asleep the brain activity is very similar to that of someone who is fully awake.
  • Perception: The active process through which people use knowledge and understanding of the world to interpret sensations as meaningful experiences.
  • Peripheral Vision : Vision emanating away from the Fovea and from the rods cell-receptors of the eyes.
  • Peristalsis: Automatic muscular movement of the intestine consisting of wave-like contractions that take place when the body is digesting food.
  • Photopic Vision: Vision through the functioning of the Cone light-sensitive cells of the eye.
  • Proprioceptors : Information transmitters of the nervous system which feed spatial orientation impulses to the brain.
  • Psychosomatic: Refers to a psychological reaction to an outside stimulus causing physiological changes or changes. It refers to the interrelationships of the mind and body.
  • Pulmonary: Referring to the lungs.
  • Regression : A symptom of stress in which correct actions are forgotten and substituted for procedures learnt in the past.
  • REM: (Rapid Eye Movements) A term used in sleep studies to define a stage of sleep. In REM sleep the EEG becomes irregular and the EOG shows the eyes rapidly darting back and forth whilst the EMG shows the muscles to be relaxed. It is suggested that during REM sleep the memory is strengthened and organized. Sometimes referred to as Paradoxical Sleep.
  • Retina: A light sensitive screen on the inside of the eye to which images are focussed. The retina has light sensitive cells, rods and cones, which convert the image into nerve impulses which are interpreted by the brain.
  • Rods: Light sensitive cells on the retina. They are sensitive to lower levels of light than the cones and are not sensitive to colour. To adapt completely to dark conditions will take the rods about 30 minutes and their adaption can be destroyed by even a transitory bright light.
  • Scotopic Vision: Vision through the functioning of the Rod light-sensitive cells of the eye.
  • Semicircular canals: The organs of the inner ear set in three planes at right angles to each other, which detect angular acceleration.
  • Skill: is an organised and co-ordinated pattern of activity. It may be physical, social, linguistic or intellectual.
  • Sleep Inertia: Transitional state of lowered arousal occurring immediately after awakening from sleep and producing a temporary decrement in subsequent performance.
  • Somatogravic Illusion : The illusion of pitching up or down as a result of the movement of the Otoliths due to linear acceleration and by the resultant vector of the g forces acting on the pilot and aircraft. The Somatogravic Illusion can result from both these two quite different effects.
  • Somatogyral Illusion : is the sensation of turning in the opposite direction that occurs whenever the body undergoes angular deceleration from a condition of persisting angular velocity.
  • Spatial Disorientation: A state characterized by an erroneous sense of position, attitude and motion of oneself or one’s aircraft in relation to a fixed, three dimensional co-ordinate system defined by the surface of the earth and the gravitational vertical. In addition, this also includes errors of perception by the aviator of his position, attitude or motion with respect to his aircraft or of his own aircraft relative to other aircraft [Benson AJ]
  • Staggers : Experienced when suffering from decompression sickness as nitrogen bubbles affect the blood supply to the brain causing the sufferer to lose some mental and body control functions.
  • Stereopsis : The ability to judge depth visually due to the principle that near objects produce images on each retina that are more different from one another than distant objects.
  • Stress : any force, that when applied to a human system, causes some significant modification of its form, where forces can be physical, psychological or due to social pressures.
  • Stroke : A term used to describe the effects of a blockage of one of the arteries to the brain. The disruption of blood flow, and therefore oxygen supply to that part of the brain will cause a failure in the ability of the brain to control a particular part of the body. Depending on the site affected, the results could be paralysis, loss of speech, loss of control of facial expression.
  • Syncope: Fainting through a fall in blood pressure.
  • Systole: See blood pressure.
  • Time of Useful Consciousness (TUC): The amount of time an individual is able to perform useful flying duties in an environment of inadequate oxygen.
  • Trachea: The main airway leading from the nose / mouth into the chest cavity. It is a cartilage reinforced tube which divides into two Bronchi which deliver air to the left and right lungs.
  • Vestibular Apparatus: The combination of the semicircular canals and the otoliths. The function of the vestibular apparatus is to provide data to the brain that enables it both to maintain a model of spatial orientation and to control other systems that need this information.
  • Vigilance (state of): The degree of activation of the central nervous system. This can vary from deep sleep to extreme alertness.
  • Window of Circadian Low (WOCL): Usually hours between 0200 and 0600 for individuals adapted to a usual day-wake/night-sleep schedule, estimated on the basis of circadian low of performance, alertness, subjective feelings of fatigue and body temperature. In aviation, for flight duty periods that cross three or less time zones, WOCL is estimated between 0200 to 0600 home base time; while it is considered to be the same period for change of 4 or more time zones for the first 48 hours only.
  • Zeitgebers: From the German phrase “time givers”, Zeitgebers are cues that serve to synchronise the internal body rhythms. Such body rhythms as temperature variations and sleep cycles may be adj usted by a change to external cues which over a period of time will allow the body clocks to adjust to, for example, a change to the time zone.

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