Aviation Physiology Flashcards
Hypoxia Symptoms
● The literal definition of hypoxia is “low oxygen”.
● Therefore, hypoxia implies a lack of sufficient oxygen for the body to operate normally.
● Its onset is insidious and may be accompanied by a feeling of well being, known as euphoria.
➢ The result is that in many cases the pilot may become seriously hypoxic without appreciating that there is a problem.
● Even minor hypoxia impairs night vision and slows reaction time.
● Without supplemental oxygen, night vision measurably declines at pressure altitudes above 5000 feet
● More seriously hypoxia impairs judgement and coordination is poor and then gives rise to unusual fatigue and, finally, results in a loss of consciousness.
● Hypoxia occurs because the the atmospheric pressure and the partial pressure of oxygen both decline at higher altitudes.
● Relatively small amounts of alcohol affect tolerance to hypoxia and rapidly deteriorates with increase of altitude
● Tolerance to–and the associated symptoms with–hypoxia will vary from individual to individual and from time to time.
➢ Tolerance can be increased by continual exposure to high altitudes.
➢ It can also vary with the level of the hemoglobin and the oxygen carrying capacity of the blood.
➢ Tolerance is decreased by fatigue, cold, and poor physical conditioning.
● Smokers are more susceptible to the effects of hypoxia because smoking increases the carbon monoxide levels in the blood and reduces lung capacity.
● To avoid hypoxia, do not fly above 10 000 ft ASL (3 050 m) without supplemental oxygen or cabin pressurization.
● ALSO: Remember that that retina of the eye is more sensitive to hypoxia than any other part of the body; one of the first symptoms of hypoxia is a decrease in night vision.
➢ For this reason, pilots flying at night are advised to use oxygen, if available, from the ground up
Gas Expansion / Trapped Gases
● Dysbarism is a condition brought about by gases trapped in the body that expand or contract in body cavities.
● This trapped gas can cause severe toothaches, ear or sinus pain. Abdominal pain is also another symptom.
● The most likely time that problems with these trapped gases will be evident is during a descent or when descending too quickly.
● Physical damage caused by these trapped gases are called barotraumas.
● The ears are most susceptible to this!
○ The problem of ear block can sometimes be helped by using the Valsalva Technique, which is to close the mouth, hold the nose, and blow gently.
● Yawning, swallowing, or chewing gum can also be used.
● If a passenger reports pain in their ears, you should level off and instruct them on how to clear their ears
Decompression
● At ground level the body tissues are saturated with nitrogen, an inert gas which makes up 80% of our atmosphere.
● As the aircraft climbs, atmospheric pressure is reduced, and by 18 000 ft (5 486 m) above sea level (ASL) atmospheric pressure is halved.
● Pilots flying aircraft with unpressurized cabins at altitudes greater than 25 000 ft (7 620 m) ASL may be subject to the “bends”
● Although decompression sickness does not normally occur below 20 000 ft (6 096 m) ASL, people who fly after scuba diving may develop the symptoms at much lower altitudes.
● Atmospheric pressure beneath the water increases by one atmosphere for every 33 ft (10 m) and divers who breathe pressurized air for more than a few minutes supersaturate their tissues with nitrogen.
● For this reason, as the aircraft ascends, nitrogen bubble formation may take place above 8 000 ft (2 432 m) ASL causing the bends
● can produce many symptoms from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its name
● After non-decompression dives, flights up to altitudes of 8000 ft (2 432 m) ASL should be avoided for 12 hours.
● Where decompression stops have been required on returning to the surface, the interval should be 24 hours.
● For flights above 8000 ft (2 432 m) ASL the interval is 24 hours regardless of the type of dive.
➢ This is because even a pressurized aircraft may lose cabin pressurization
Vision
● Because the cones in the eye require a lot of light to function properly, at night pilots can experience reduced vision.
● Using your peripheral vision may help in this case.
➢ Look at things off center.
● Flashlights should have a red filter.
➢ A red light does not cause the eye to adjust to it as does bright white light.
Scanning
● Scanning should be done by segmenting the windshield and examining each segment for aircraft before moving on to the next segment.
● Objects which are growing larger but not moving horizontally or vertically are the hardest to spot and the most dangerous.
Orientation / Disorientation
● Spatial disorientation can occur if you become confused about your sense of position or movement.
● Vertigo is a sense or hallucination of spinning or moving even after motion has stopped.
● Fluid in the inner ear is moved when the body is moved and sensed by the brain which gives us our sense of equilibrium.
● Illusions caused by linear acceleration or deceleration are referred to as Somatogravic illusion
➢ Acceleration gives the illusion of climbing (nose up)
➢ Deceleration gives the illusion of descending (nose down)
➢ Banks give the illusion of level flight.
➢ The Leans happen when you enter a banked turn too slowly. For example, if you don’t roll quickly enough into a left turn, the fluid in your ears won’t start moving, and your brain thinks you’re still straight-and-level. If you correct your wings back to level flight abruptly, your ears and brain think they’re banking in the opposite direction (to the right). This makes you feel like you need to roll the airplane back to the left, or lean your body in that direction to be ‘upright’.
● When the aircraft is established in a turn the fluid in the inner ear incorrectly indicates that the turn has stopped or if the turn stops (back to level) the fluid will indicate a turn in the opposite direction.
● These illusions will be especially strong at night or in instrument conditions and are called vestibular (ear) illusions
Body Rhythms / Jet Lag
● Jet lag is caused by the disturbance of the circadian rhythm by moving through different time zones.
➢ Symptoms can include insomnia, disruption of bodily functions, irritability etc
● Drugs should not be used to fight jet lag, the body will eventually accustom itself to the new rhythm.
➢ It takes approximately one day per time zone change to get into a new rhythm.
● Our circadian rhythm makes us least alert between 0200 - 0559 at the location where the flight crew member is acclimatized
Sleep / Fatigue
● Almost every analysis of aircraft accidents points to the need for more crew rest.
● Fatigue can be caused by many things besides a lack of sleep.
➢ Including things like stress, noise, eye strain, vibration, temperature variation, heavy workload, poor diet, boredom, etc.
Anesthetics / Blood Donations
● When a local anesthetic is used for an extensive dental procedure, pilots should wait at least 24 hours before flying.
● Generally, active pilots should not donate blood, but if blood has been donated the pilot should wait at least 48 hours before flying
Carbon Monoxide
● This is a colorless, odorless, and tasteless gas.
● Hemoglobin has 210 times the affinity for carbon monoxide than it has for oxygen.
● The body requires up to 48 hours to dispose of carbon monoxide.
● As altitude increases susceptibility to carbon monoxide poisoning increases.
● The symptoms of carbon monoxide poisoning are insidious.
➢ Initially, there is an inability to concentrate,
➢ thinking becomes blurred, and
➢ subsequently dizziness and headache develop.
● If any of these symptoms are noticed, pilots should turn off the heater, open the air ventilators and descend to a lower altitude if it is safe to do so.
● If oxygen is available, it should be used.
Night Vision
● The retina of the eye is more sensitive to hypoxia than any part of the body; one of the first symptoms of hypoxia is a decrease in night vision.
➢ For this reason, pilots flying at night are advised to use oxygen, if available, from the ground up.
● Many factors affect vision.
● At night, cockpit lights should be kept low to maintain the dark adaption needed to see clearly outside the cockpit.
● It takes dark adaptation about 30 minutes to adjust to each new light setting.
● There is a blind spot in the centre of the eye at night.
● The same scan is required at night, with one difference: the part of the eye that is best suited for night vision is not in the centre.
➢ An object detected in barely adequate light will disappear if viewed directly, but will often reappear if one looks 10 to 15° to one side of the object.
➢ To improve dark adaption, pilots should use sunglasses during the day to avoid eye fatigue
Hyperventilation
● Hyperventilation is breathing at a faster and/or deeper rate than the body requires for good oxygenation at the existing work level.
● The rate of breathing is controlled by the amount of carbon dioxide in the lungs and in the blood.
● In hyperventilation, carbon dioxide is blown off and its level in the blood drops below normal.
● Pilots may notice slight dizziness, a feeling of coldness, a sensation like a tight band around the head, and pins and needles in the hands and feet
● Hyperventilation most commonly occurs in association with anxiety, fear, or during intense concentration on a difficult task such as performing a complicated instrument procedure.
● To recover from hyperventilation
➢ Consciously slow the rate of breathing to 10-12 breaths per minute,
➢ and do not breathe deeply.
➢ Keep the respiratory rate slow until the symptoms disappear and then resume a normal breathing pattern
Effects of Smoking
● Smoking is a source of carbon monoxide.
● Smokers carry some carbon monoxide in their blood all the time, and may have 5 to 10% of their haemoglobin saturated with carbon monoxide.
● This reduces the oxygen-carrying capacity of the blood and smokers may become hypoxic at altitudes below 10 000 ft ASL (3 050 m).
Time of Useful Consciousness
● The amount of time an individual is able to perform flying duties efficiently in an environment of inadequate oxygen supply.
● A rapid decompression can reduce the TUC by up to 50%
Effects of G Forces
● Tolerance is increased due to good physical conditioning and to continued exposure.
● During the manoeuvres, tensing the calves and thigh muscles increases tolerance.
● Positive G forces (head to foot so no blood in head) can also cause something called Stagnant Hypoxia, where the blood is unable to be pumped to the head.
● Negative G forces can result in redout, where the blood gathers in your head causing everything to have a reddish tinge.
Hypoxic hypoxia
● Hypoxic hypoxia is the result of low oxygen levels in the bloodstream.
● In pilots, this most often occurs with exposure to altitude (hypobaric hypoxia).
● At low altitudes, the partial pressure of oxygen in the atmosphere is adequate to maintain brain function at peak efficiency.
● At 8 000 ft ASL (2 440 m), some people may notice a slight increase in heart rate and speed of breathing (respiratory rate).
● By 10 000 ft ASL (3 030 m), all pilots will experience mild hypoxia and some will become symptomatic.
Anaemic hypoxia
● Oxygen in blood is carried by haemoglobin, which is found in red blood cells.
● When the red blood cell count decreases, or the haemoglobin does not function properly, less oxygen can be carried.
● This can occur in carbon monoxide poisoning
● A person suffering from anaemia may notice symptoms such as breathlessness, fatigue, or chest pain, and symptoms will worsen at higher altitudes, as the effects of hypoxia and anaemia are additive
Ischaemic hypoxia / Stagnant hypoxia
● ischaemic hypoxia occurs when there is inadequate blood flow to body tissues.
● This can occur with constriction of blood vessels (cold) as well as low blood pressure and fainting, or high accelerations
Histotoxic Hypoxia
● Histotoxic hypoxia refers to an inability of the cells of the body to use the oxygen available.
● cyanide poisoning, chemical poisoning, and intoxication with certain drugs or alcohol.
Empty-field myopia
● It is a condition in which eyes have nothing specific within the available visual field upon which to focus.
● sunny conditions over a cloud layer or the flight course is in the direction of the sun; or flying over snow covered or desert surfaces with predominantly featureless ground characteristics and over large bodies of water;
● While scanning, take an object on the horizon, focus on it and then scan all sectors of the sky, refocusing as needed
