Lecture 4-Aviation Human Factors

Remember Decompression means loss of pressurization. Flying with the aircraft that loss of pressurization will expose the crew/passengers to: Hypoxia, Hyperventilation, Decompression sickness, Trapped gas expansion.

Contents Hyperventilation Trapped Gas Decompression Sickness (Evolved Gas Disorders)

HYPERVENTILATION

Breathing Breathing: process of taking air (O 2 )into the lung and exchanging gas (CO 2 )to the environment. CO 2 is the gas produce by all living cells It is important for maintaining chemical balance and control our breathing. Removing of CO 2 from the body is limited by the lung during exhalation. When human expose to situation of emotional stress, breathing become fast and can cause hyperventilation.

Hyperventilation Hyperventilation is simply a matter of rate and depth breathing increases rapidly. It causes the excessive loss of CO 2 from the blood. This results to degrade the chemical balance in the blood. Also can affect the brain, as the CO 2 levels in the brain reduces.

Hyperventilation CAUSES It caused by emotional reaction such as anxiety, fear, stress and anger.

Hyperventilation SYMPTOMPS Dizziness Lightheadedness Blurred Vision Numbness Tingling Hot and cold sensations. Muscle incoordination. Unconsciousness: due to respiratory systems overriding mechanism to regain control of breathing.

Hyperventilation & Hypoxia Hyperventilation: Usually occurs below 10,000. Skin may look pale. As we ascend, it can occur slowly and gradually over time. Hypoxia: Usually occurs above 10,000. Skin may look blue cyanosis. Can occur rapidly.

Treatment of hyperventilation Best method is to voluntarily reduce rate of breathing Normal rate is breaths per minute Avoid panic Go to 100% O 2 (if available) Talk or sing (to increase CO 2 level) If severe or combined with hypoxia, return to ground level. Breathing into a bag.

TRAPPED GAS

Boyle’s Law Pressure decrease, Volume increase Site level 10,000 feet 18,000 feet 25,000 feet 43,000 feet

Boyle’s Law Gases within the body are influenced by pressure and temperature changes outside the body Ascent – pressure is decreased and gases expand. Descent – pressure is increased and gases contract. The body can withstand changes in total pressure as long as the air pressure within the body cavities is equalized to ambient pressure

Trapped Gas Body cavities most often affected Middle ear Sinuses Teeth Stomach & Intestines (Gastrointestinal tract)

Trapped Gas 1. Middle Ear FRONTALS ETHMOIDS SPHENOID MAXILLARY 2. Sinus 3. Stomach and Intestines 1. Teeth

Anatomy of Ear

17 The ear is not only an organ of hearing but also one of regulating equilibrium. When ascending to altitude, aircrew members often experience physiological discomfort during changes in atmospheric pressure. Ear

The Middle Ear Ascent to altitude As ambient pressure decreases with ascent, gas expands within the middle ear Air escapes through the Eustachian tubes to equalize pressure As pressure increases, the eardrum bulges outward until a differential pressure is achieved and a small amount of gas is forced out through eustachian tube and the eardrum relaxes.

The Middle Ear Descent to altitude Equalization of pressure does not occur automatically Eustachian tube performs as a flap valve and allows gas to pass outward easily, but resists the reverse. During descent the ambient pressure increase, the flap valve can stop the returning air into the middle- ear to equalize the pressure. If pressure is not equalized Ear block may occur and it is extremely difficult to reopen the eustachian tube The eardrum may not vibrate normally and decreased hearing results (minor hearing lost)

Middle Ear Block

Ear Block Symptoms “Ear congestion” Ringing in the ears. Inflammation. Discomfort. Pain. Temporary impairment of hearing Bleeding (severe cases) Eardrum rupture Contributing Factors Flying with head cold Flying with a sore throat

Middle Ear Discomfort A cold can produce enough congestion around the eustachian tube to make equalization difficult. This causes and ear block causing a build up in pressure that can be very painful. Severe ear pain and loss of hearing that can last several hours to several days. Can cause rupture of the ear drum Usually occurs on descent

Ear Block Treatment Treatment Yawning or swallowing Performing “Valsalva” Nasal sprays – best used prior to descent Pain medications For infants / children – provide a bottle / straw to suck Ascend to safe altitude where symptoms subside and then slowly descend

Ear Block Prevention Prevention DO NOT FLY WITH A HEAD COLD “Stay ahead of your ears” Valsalva during descent

Delayed Ear Block Occurs in situations where crew members breath 100% oxygen at altitude, especially if oxygen was maintained during descent to ground level Symptoms occur 2 to 6 hours after descent Oxygen in the middle ear is absorbed and creates a decreased pressure Prevention – valsalva numerous times after altitude exposure to prevent absorption

Sinus Sinus is the cavity within a bone, especially in the bones of the face. FRONTALS ETHMOIDS SPHENOID MAXILLARY

The Sinuses Most often involves frontal sinuses (above each eyebrow) and maxillary sinuses (both cheeks) Sinus ducts have openings into the nasal passage Gas escaped with increases upon ascent most often without problems With descent, air moves back out through the ducts if they are open If the openings are swollen, a blockage may occur.

The Sinuses Symptoms Severe pain Possible referred pain to teeth Treatment Equalize pressure as quickly as possible Valsalva is sometimes effective Coughing against pressure is effective Ascent to safe altitude then slow descent Nasal sprays may help

The Teeth Air trapped within teeth expands with ascent. Pain often increases with altitude. Rarely caused by a root abscess with a small pocket of trapped gas

The Teeth (Barodontalgia) Treatment / Prevention Descent Pain medications Good dental hygiene

Gastrointestinal Tract Gastrointestinal: related to stomach and intestines Most frequently experienced with a rapid ascent (decrease in barometric pressure) Symptoms result from gas expansion Above 25,000 feet distention could be large enough to produce severe pain May produce interference with breathing

Gastrointestinal

Gastrointestinal Tract

Sources of Gas Swallowed air (including gum chewing) Food digestion Carbonated beverages Treatment Walking or moving Massage the affected area Loosen restrictive clothing Use of a gas reducing agent Descent to a higher pressure Gastrointestinal Tract

DECOMPRESSION SICKNESS

Henry’s Law Nitrogen dissolved in the blood responds in same way. Carbonated drink: Once the seal is opened, the gas that has been under pressure escapes, gas that has been dissolved in the drink also begins to escape by forming bubbles. Henry’s Law: Pressure of gas decrease, the gas in the in the liquid also decrease.

Decompression sickness Decompression sickness is caused by nitrogen forming as bubbles in the blood. As pressure decreases, gases (nitrogen) dissolved in body fluids are released as bubbles. Can occur in the blood, other fluids, or in the tissues This sickness refer to the nitrogen saturation of the body. This is related to the inefficient removal and transport of the expanded nitrogen gas volume from the tissues to the lungs.

Remember Composition of gas in atmosphere consists of: 78% nitrogen, 21% oxygen and 1% are amounts of other gases.

Decompression sickness Tissues and fluid of the body contain from 1 to 1.5 litres of dissolved nitrogen, depending on the pressure of nitrogen in the surrounding air. As altitude increases, the partial pressure of atmospheric nitrogen decreases and nitrogen leaves the body to re-establish equilibrium. If the change is rapid, recovery of equilibrium lags, leaving the body supersaturated.

Decompression Sickness Type I (Non-Serious) Bends Skin Manifestations Type II (Serious) Chokes Neurological Manisfestations

The Bends Generally located around / near articulating joints of the body Pain from mild to unbearable Factors of exercise, increased altitude, and increased time of exposure will increase severity of symptoms Descent to below altitude of onset Decompression Sickness (DCS)

Skin manifestations Mild Tingling of the skin Believed to be caused by bubbles of gas evolving under the skin Symptoms themselves are not serious HOWEVER they are a WARNING that bubbles may form elsewhere Continued exposure may lead to more serious forms of decompression sickness

The Chokes Rare but potentially life-threatening Nitrogen bubbles in the blood vessels of the lungs Symptoms Deep and sharp pain or burning sensation under the sternum Shortness of breath Dry, progressive, nonproductive cough Feeling of suffocation with decreasing ability to take a breath Results in hypoxia Decompression Sickness (DCS)

Neurologic Manifestations (CNS) Very rare Rarely may effect brain or spinal cord More common Visual disturbances (blind spots, flushing, or flickering vision – Scotoma) Persistent headache Partial paralysis Inability to speak or hear Loss of orientation

Factors Affecting DCS Scuba diving Hydration level Repeated exposures Length of time at altitude Rate of ascent Altitude (18,000ft)

Severity and Rapidity of Onset Related to Rate of ascent More rapid = sooner symptoms appear Altitude Below 25,000 feet is rare Above 25,000 feet may occur after leveling off Duration of exposure Physical activity Exercise lowers the threshold for manifestations, particularly the bends Individual susceptibility Unpredictable

SCUBA Diving Greatly lowers threshold altitude for the occurrence of decompression sickness when flying Cases of decompression sickness have occurred in individuals who fly in cabins as low at 5,000 feet If within 6 hours of diving Recommended at least 24-hour delay between diving with SCUBA and flying

Decompression Sickness (DCS) Emergency Treatment 100% oxygen for everyone onboard Declare an emergency Descent as rapidly as possible Immobilize affected areas Treat shock Land as soon as possible Medical evaluation by a QUALIFIED flight surgeon / hyperbaric physician ASAP Decompression chamber therapy if required

Prevention In high-altitude flight, aircrews can be protected against decompression sickness. Protective measures include: De-nitrogenation. Cabin pressurization. Limitation of time at high altitude. Aircrew restrictions. 49