Lecture 4 Trapped gas and decompression sickness Aviation Human Factors

Review on Last Chapter 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.

Introduction Human physiology is evolutionary adapted to be efficient up to 12,000ft above sea level. Outside this zone, physiological compensatory mechanism may not be able to cope with the stresses altitude. Besides hypoxia, the changes in pressure will result in air or flight sickness which are: Trapped Gas Decompression Sickness (Evolved Gas Disorders)

TRAPPED GAS

PRESSURE DECREASE, VOLUME INCREASE Boyle’s Law 43,000 feet 25,000 feet 18,000 feet 10,000 feet Site level PRESSURE DECREASE, VOLUME INCREASE

Boyle’s Law Gases within the body are influenced by pressure and temperature changes outside the body Ascend – pressure is decreased and gases expand. Descend – 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

Boyle’s Law

Trapped Gas Trapped gas means the gas can’t be released especially by our body cavities part. Our body cavities that often experienced trapped gas are: Middle ear Sinuses Teeth Stomach & Intestines (Gastrointestinal tract)

4. Stomach and Intestines Trapped Gas 2. Sinus FRONTALS ETHMOIDS SPHENOID MAXILLARY 1. Middle Ear 3. Teeth 4. Stomach and Intestines

Anatomy of Ear

Anatomy of Ear

Ear 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.

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.

Trapped Gas Expansion

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)

Ear Block

Processes: How middle ear is affected when a person is flying into higher altitude Middle ear is on of the part of body cavities that being affected by the trapped gas. When the aircraft ascent to high altitude, the atmospheric pressure drop causing the gases within the body to expand. The expanded gas escape from body through the Eustachian tube located at middle ear to equalize the pressure.

Processes: How middle ear is affected when a person is flying into higher altitude The eardrum will bulge outwards to allow the gases escape from the body until the differential of the pressure is achieved and then back to it form after several force that push the gasses outward to achieve the equilibrium. When the aircraft descend, the sudden change of increasing of atmospheric pressure will force the gasses within the body to contract.

Processes: How middle ear is affected when a person is flying into higher altitude This will cause the body lose it equilibrium because the pressure outside the body is higher than within the body. One way to achieve it is that, the gasses will be push through Eustachian tube. Since Eustachian tube act like a flap valve, it will function to prevent the gasses from losing. If the Eustachian tube is blocked , the middle ear block will happen and it is extremely difficult to re-open the Eustachian tube. The person will feel uncomfortable and pain.

Ear Block – Contributing Factor Contributing Factors Flying with head cold 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. Flying with a sore throat

Ear Block - Symptoms Symptoms “Ear congestion” Ringing in the ears. Inflammation. Discomfort. Pain Temporary impairment of hearing Bleeding (severe cases) Eardrum rupture

Middle Ear Discomfort 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 more critical during descent compare to ascend.

Ear Block Prevention Prevention DO NOT FLY WITH A HEAD COLD “Stay ahead of your ears” Valsalva during 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 Valsalva… Yawn, Chew, Swallow Slow descent rate Post Flight Ear Block: Caused by absorbsion of O2 within the middle ear TREATMENT = Frequent Valsalva

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

The Sinuses Like the middle ear, sinuses can also trap gas during flight. The sinuses are air-filled, relatively rigid, bony cavities lined with mucous membranes. They connect with the nose by means of one or more small openings. The two frontal sinuses are within the bones of the forehead; the two maxillary sinuses the two ethmoid sinuses

The Sinuses If the openings into the sinuses are normal, air passes into and out of these cavities without difficulty and pressure equalizes during ascent or descent. Swelling of the mucous membrane lining, caused by an infection or allergic condition, may obstruct the sinus openings These conditions may make it impossible to equalize the pressure.

The Sinuses Change of altitude produces a pressure differential between the inside and the outside of the cavity, sometimes causing severe pain.

The Sinuses Symptoms Treatment 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

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

DECOMPRESSION SICKNESS

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. When the atmospheric pressure is decreased rapidly to certain critical values, the nitrogen pressure gradient between the body and the outside air is such that nitrogen will come out of solution in the form of bubbles Can occur in the blood, other fluids, or in the tissues Symptoms do not appear rapidly

Henry’s Law 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. Nitrogen dissolved in the blood responds in same way.

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

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

Decompression Sickness (DCS) The Bends (Pain in large joints) 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

Decompression Sickness (DCS) Skin manifestations 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

Decompression Sickness (DCS) 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 Feeling of suffocation with decreasing ability to take a breath Results in hypoxia

Decompression Sickness (DCS) Neurologic Manifestations Very rare Rarely may effect brain More common Visual disturbances (blind spots) Persistent headache Partial paralysis Inability to speak or hear Loss of orientation

Factors Affecting DCS Scuba diving 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 Time at altitude. The longer one is at an excessive altitude, the greater the risk for developing DCS because more bubbles can form and be transported throughout the body. Rate of ascent. The more rapid the ascent, the greater the chance of bubble formation because the body has little time to equalize the pressure changes. Altitude. 4. Age and obesity. Older people tend to be more susceptible to DCS under minimal conditions. The same is true for obese people whose fat will store more gas and nitrogen. It is also suspected that recent alcohol use can increase the risk. 6. Repeated exposure. Taking several flights over a short period of time (48 hours) increases the chances of problems. Repeated physiological “insults” to affected organs make them more susceptible. The threshold for developing DCS problems is usually above 18,000 feet. Increases more rapidly above 26,000 feet.

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: Cabin pressurization. Limitation of time at high altitude.

Quick notes about evolved gas disorders Rate of ascent, altitude, body fat, exercise, duration and repeated exposure are factors that increase the risk of having an evolved gas disorder pressurized cabins and denitrogenation are recommended for prevention if it occurs, get the individual to ground level immediately, give him 100% O2 seek medical attention and compression therapy

Summary Trapped Gas: Expanding gases within the body cannot escape to allow the equalization of body pressures. Decompression Sickness: Occurs when gases dissolved in body fluids are released as bubbles.