Aerospace Physiology

Identify the important factors in normal respiration.

oxygen carbon dioxide d c c b b

Recall the signs and symptoms of hyperventilation.

signs - Most often observed in hyperventilation are increased rate and depth of breathing, muscle tightness and twitching, paleness, cold clammy skin, muscle spasms, rigidity and unconsciousness. Symptoms — Most often noted are dizziness, faintness, slight nausea, numbness, tingling or coolness and muscle tremors.

List the phases of respiration.

ventilation, diffusion, transportation and utilization

Recall the similarities of treatment for hypoxia and hyperventilation.

when you treat for hyperventilation, you are also treating for hypoxia.

Recall the corrective actions for suspected decompression sickness.

--Immediate descent --See flight surgeon

Identify the advantages and disadvantages of pressurization systems.

Advantages- Note — The primary purpose for aircraft pressurization is to reduce the possibility of DCS and hypoxia. Disadvantages- Decompression 4. Reduced expansion of gastrointestinal trapped gas 5. Controls cabin temperature, humidity, and ventilation within a desired comfort range 6. Allows the crew and passengers to move freely within large cabins unencumbered by oxygen equipment 7. Minimizes fatigue and discomfort of crew and passengers during long flights (air evacuation, troop transport, etc.). 8. Protects the sinuses and middle ears from sudden pressure increases during descents by slowly scheduling the cabin descent

Identify the areas of the body most likely to be affected by trapped gases and when it is most likely to occur.

Middle Ear GI tract Teeth Sinuses

List structures that are important to respiration.

Oral-Nasal Cavities (mouth, pharynx,etc Trachea (windpipe) Lungs Alveoli Composition of Inspired Air

Dalton's Law

The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture. The pressure exerted by each gas in a mixture is independent of other gases in the mixture. For example, the total pressure of the atmosphere at sea level is 760 mmHg this pressure equals PN2 + PO2 + PCO2 and the partial pressure of other trace gases. Dalton's Law explains how exposure to a high ambient altitude can reduce the available oxygen. As ambient altitude increases, the partial pressure of oxygen (PO2) decreases even though the percentage of oxygen remains the same. For example, at sea level the PO2 is 21 percent of 760 mmHg or 160 mmHg. Correspondingly, with a reduction of total pressure, the partial pressure of each gas will decrease. At 18,000 feet, PO2 is 21 percent of 380 mmHg or 80 mmHg.

Ventilation

The volume of gas exchanged between the lungs and the ambient environment per unit time. This process is regulated to provide adequate delivery of oxygen and removal of carbon dioxide to satisfy the demands of metabolism.

Recall the common units of measurement for atmospheric pressure.

The weight of the atmosphere can be measured in pounds per square inch (psi), millimeters of mercury (mmHg), or inches of mercury (inHg). Atmospheric pressure readings will vary daily, depending on changing surface temperatures and high and low pressure areas.

Recognize the description and common unit of measure of the U.S. Standard Atmosphere.

U.S. Standard Atmosphere was computed by taking the average pressure and temperature readings for a year at mid-latitude locations. At sea level, these readings were determined to be +15 °C and 760 mmHg (29.92 inHg) pressure. Figure 1-2 shows the U.S. Standard Atmosphere pressures at various altitudes. The pressure at 18,000 feet is 379.4 or about one half of the pressure encountered at sea level. This illustrates that the greatest pressure change occurs at lower atmospheric levels between sea level and 18,000 feet.

Utilization

Utilization — Cellular metabolism. This phase involves the use of oxygen in energy production and the production of carbon dioxide and water.

List the steps for emergency treatment of hyperventilation.

1. Maximum oxygen under pressure 2. Connections - check security 3. Breathe at a Rate and Depth Slightly Less Than Normal Until Symptoms Disappear 4. Descend Below 10,000 Feet MSL and Land as Soon as Possible

Identify which gases are present in the atmosphere and their associated percentage of the total composition.

78 percent nitrogen, 21 percent oxygen 1 percent other gases (including 0.03 percent carbon dioxide). These percentages remain relatively constant with increased altitude.

Diffusion

Diffusion - Oxygen and carbon dioxide pass through the alveolar membrane and capillary walls.

Identify the factors that influence hypoxia.

Altitude Rate of Pressure Change Duration of Exposure Individual Tolerance Physical Activity Self-Imposed Stress

Identify the signs and symptoms of hypoxia onset.

Blueness of skin Mental confusion poor judgment euphoria belligerence rate or depth of breathing

Boyle's Law

Boyle's Law When the temperature remains constant, as in the human body, a volume of gas is inversely proportional to the pressure surrounding it. This principle explains why a balloon expands as it ascends and also why a volume of air expands when trapped in a body cavity when the pressure is reduced around it. Boyle's Law explains for the effects of pressure changes in the ears, sinuses, teeth and gastrointestinal tract.

Boyle's Law

Boyle's Law states the volume of a gas is inversely proportional to the ambient pressure. Therefore, changes in ambient pressure during flight will result in changes in the volume of body gases.

Identify the basic cause of trapped gas disorders.

Boyle's Law states the volume of a gas is inversely proportional to the ambient pressure. Therefore, changes in ambient pressure during flight will result in changes in the volume of body gases. The human body can withstand these changes, including expanding gas pressure buildup, when the pressure can be relieved. However, difficulty (usually in the form of pain) results when the expanding gas cannot escape. The gas is then considered "trapped." With further decrease of ambient pressure (ascent), a greater increase in volume or pressure within the cavity occurs. These increases sometimes result in pain. Figure 3-2 shows the areas most often affected by the change in pressure.

Charles' Law

Charles' Law When volume is constant, the pressure of a gas increases or decreases proportionally to an increase or decrease in its temperature. Evidence of this law can be seen in the small decrease in pressure recorded from an oxygen cylinder taken from ground level on a hot day to an unpressurized aircraft altitude of 10,000 feet. Consequently, the cooler temperature at this altitude leads to a decrease in the pressure within the cylinder.

Recall symptoms of trapped gas disorders.

Ear Block-If the pressure differential of the atmosphere over the middle ear exceeds 80 mmHg, it may be impossible to open the Eustachian tube with equalization pressure methods. Sinus Block- However, if the sinus ducts are swollen because of an upper respiratory infection, there may be a blockage of the ducts. Sinus/Tooth Blockage of the ducts leading to the maxillary sinuses may be mistaken for upper tooth pain because of their proximity to the upper teeth. Expansion of Trapped GI Gas-A problem that may be experienced with a decrease in atmospheric pressure is discomfort from expansion of gases in the GI tract -----(2) The relative change in volume produced by the same change in pressure is greater for a wet gas than for a dry gas.

List the physical indications of rapid decompression.

Explosive Noise Windblast/Flying Debris Fogging Temperature Pressure

Henry's Law

Henry's Law The amount of gas in a solution varies directly with the partial pressure of that gas over the solution. Therefore, if pressure is reduced above the solution, some gas will come out of solution. This principle explains why carbon dioxide bubbles are released when a carbonated beverage container is opened or why nitrogen bubbles may come out of solution in body tissues during ascent. The nitrogen bubbles can lead to altitude-induced decompression sickness.

Henry's Law

Henry's Law states the amount of gas in a solution varies directly with the partial pressure of that gas over the solution. When the atmospheric pressure is decreased, the pressure difference between gases dissolved in body fluids and the ambient air may cause dissolved gases to come out of solution in the form of bubbles. This process can occur in the blood, other body fluids, and or body tissues.

Histotoxic Hypoxia

Histotoxic Hypoxia — Results when the O2 delivered to the cells cannot be used for energy production. Adequate O2 is available to the lungs and the blood is capable of carrying it to the tissues. However, the tissues and cells are unable to use the available O2. The primary cause of histotoxic hypoxia in a crewmember is cyanide. Cyanide, in the form of hydrogen cyanide gas (HCN), is a by-product of the combustion of plastics, insulation, seat covers, and other synthetic substances found on aircraft. HCN is highly toxic and extremely small concentrations (300 parts per million) cause incapacitation within seconds; death occurs within minutes. Therefore, you must not hesitate in donning oxygen equipment and breathing 100 percent oxygen. Secondary causes of histotoxic hypoxia are alcohol and some medications. To reduce the possibility of mishaps, AFI 11-202, Volume 3, General Flight Rules, restricts alcohol consumption 12 hours prior to flight. OPNAVINST 3710.7 restricts alcohol consumption for 12 hours prior to flight planning. Both USAF and USN instructions restrict medication unless prescribed by a flight surgeon.

Hypemic Hypoxia

Hypemic Hypoxia — Occurs when the O2 carrying capacity of the blood is reduced. Hypemic hypoxia affects O2 delivery by reducing the functional hemoglobin available for transporting O2. Certain drugs and chemicals can combine with or alter the characteristics of hemoglobin and reduce its O2 carrying capacity. For example, hemoglobin has an affinity for carbon monoxide (CO) about 200-250 times greater than with O2. The threat of inhaling carbon monoxide from smoke or fumes in the cockpit can be eliminated by using 100 percent oxygen. Smoking cigarettes prior to flight increases the amount of CO in the bloodstream and raises your physiological altitude. You then become more susceptible to hypoxic hypoxia because of the preexisting hypemic hypoxia. Blood donation and bleeding injuries also deplete the RBC/hemoglobin supply and cause hypemic hypoxia. Therefore, donating blood while on flying status is not recommended. If you choose to donate blood you will be grounded for a period of time. (USAF: 72 hours; USN: up to 28 days)

Recall the definition and causes of hyperventilation.

Hyperventilation is a condition in which the rate and or depth of breathing is abnormally increased. This increase causes an excessive loss of carbon dioxide (CO2) from the blood. The excessive loss of CO2 changes the acid-base balance of the blood making it more alkaline. but the primary cause of hyperventilation in crewmembers is emotional; e.g. fear, anxiety or stress. Voluntary Involuntary

Identify the definition of hypoxia.

Hypoxia is an oxygen (O2) deficiency sufficient to cause impairment of function. It occurs most frequently when protection against the fall in O2 partial pressure at altitude fails.

Hypoxic Hypoxia

Hypoxic Hypoxia — Results when there is a reduction of the PO2 in the lungs. Hypoxic hypoxia is usually caused by exposure to low barometric pressure and is frequently referred to as altitude hypoxia. This reduced oxygen partial pressure can result from oxygen equipment malfunctions, improper use of oxygen equipment, and loss of cabin pressurization at altitude. It can also be produced by lung diseases such as emphysema. The altitude threshold for hypoxic hypoxia is generally considered 10,000 feet MSL.

Describe the different pressurization systems.

Isobaric Pressurization- Aircraft pressurization may be regulated by maintaining a constant cabin pressure (isobaric system) as aircraft altitude increases. Isobaric Differential Pressurization- the aircraft is unpressurized until a preset cabin pressure is reached. Once reached, the isobaric function of the system maintains a constant pressure within the cabin until a selected pressure differential (cabin pressure versus ambient pressure) is attained.

Define partial pressure and identify its notation.

Partial Pressure is defined as the amount of pressure that a single gas out of a mixture of gases contributes to the sum or total pressure of that mixture. The denotation for the partial pressure of Nitrogen, Oxygen, and Carbon Dioxide is PN2, PO2, PCO2, respectively.

List the physiological divisions of the atmosphere.

Physiological Zone The physiological zone extends from sea level to approximately 10,000 feet and is the zone the human body is adapted to. Life above this zone requires considerable acclimatization. During ascent in the physiological zone, atmospheric pressure drops from 760 mmHg to 523 mmHg. Even though the oxygen partial pressure (PO2) falls, the body's compensatory mechanisms keep oxygen delivery within normal limits. Only at the upper boundary of the physiological zone and in tissues with very high O2 requirements, e.g., the retina, are symptoms of O2 deficiency noted. When flying unpressurized above 10,000 feet MSL, the use of supplemental oxygen is required. Also, trapped gas problems in body cavities can be a problem if not dealt with effectively. Physiological Deficient Zone This zone extends from approximately 10,000 feet to approximately 50,000 feet. Because of reduced atmospheric pressure, inadequate oxygen is available to sustain normal physiologic functions. Also, decompression sickness (caused by evolved gas) can occur in the body tissues and joints. This phenomena will be covered in later chapters. Atmospheric pressure decreases from 523 mmHg at 10,000 feet to 87 mmHg at 50,000 feet. Pressure suits are required above FL500. Space Equivalent Zone The space equivalent zone exists above 50,000 feet. The physiological problems of flight above 50,000 feet are essentially the same as those for space. The need for protection in a sealed cabin or pressure suit, the problem of ebullism (tissue water vaporization) above 63,000 feet, and other adverse influences on the body make this area of the atmosphere extremely hazardous for the human body (Figure 1-3).

Identify the procedures to treat hyperventilation.

Since hyperventilation and hypoxia may be confused or occur at the same time, identical corrective procedures should be followed. 1. Maximum oxygen under pressure 2. Connections - check security 3. Breathe at a Rate and Depth Slightly Less Than Normal Until Symptoms Disappear 4. Descend Below 10,000 Feet MSL and Land as Soon as Possible

Recall the types of decompression and characteristics of each.

Slow Decompression Rapid Decompression

Stagnant Hypoxia

Stagnant Hypoxia — Occurs when reduction in cardiac output, pooling of the blood, or restriction of blood flow reduces O2 delivery. Several conditions cause stagnant hypoxia. Two of these will be discussed in detail during subsequent instruction — hyperventilation and acceleration (G forces). Stagnant hypoxia can also be caused by shock (blood pooling in dilated blood vessels) or cold temperatures (constricting the blood vessels of the extremities, causing pooling of blood in the body core). Even sitting very still for long periods of time can result in stagnant hypoxia. An individual passing out while standing in formation is an example of stagnant hypoxia.

Identify the common types and causes of decompression sickness.

The Bends — The evolution of nitrogen bubbles into the joints of the body, causing pain. The pain is generally localized in and around the bony joints of the body. --Immediate descent Neurological Manifestations- One explanation for these symptoms theorizes the bubbles of evolved nitrogen circulate through the brain, reducing blood flow and causing localized, small regions of the brain to become hypoxic. -stroke: disturbances in vision, -evere persistent headache --Immediate descent Chokes-symptoms are very similar to those of a heart attack --hypothesis is that bubbles evolve in the smaller blood vessels in the lungs and in the tissue of the trachea (windpipe). The symptoms are deep sharp pain centrally located under the sternum (breast bone), a dry progressive cough, and difficulty with inspiration. --Immediate descent Skin Manifestations- In some instances, a mottled, reddish or purplish rash develops on the skin. --bubbles in and around the skin

The Law of Gaseous Diffusion

The Law of Gaseous Diffusion A gas will diffuse from an area of higher concentration or pressure to an area of lower concentration or pressure until equilibrium is reached. The speed of this movement depends on the relative concentrations of the gases (strength of the diffusion gradient). The physiological significance of this law relates to transfer of gases between the blood or other body fluids and the tissues they contact. For example, the gas transfer that takes place in the lungs by oxygen moving out of the lungs to the bloodstream and carbon dioxide moving from the bloodstream into the lungs.f

Explain how to treat and prevent trapped gas disorders.

The Valsalva Maneuver — Equalizing air pressure during descent may be accomplished by swallowing, yawning, tensing the muscles in the throat, moving the head from side to side, extending the jaw forward or rocking the jaw from side to side. However, the most effective way to equalize the pressure in the middle ear is the use of the Valsalva maneuver; force air into the middle ear by closing the mouth, pinching the nose closed and forcefully exhaling.

Recognize the functions of the atmosphere.

The atmosphere provides some unique functions that help sustain our existence on Earth. 1. It contains oxygen, essential for animal life and carbon dioxide, essential for plant life. 2. It is a shield that attenuates cosmic and ultraviolet radiation. 3. Precipitation occurs in the atmosphere, helping maintain the temperature and climate.

Recognize the potential characteristics of the onset of hypoxia.

The insidious onset is hypoxia's most dangerous characteristic. Hypoxia symptoms do not normally cause discomfort. In fact, many individuals perceive their symptoms as quite pleasant. During a slow decompression (where the cabin altitude gradually increases), hypoxia has a slow onset and the symptoms may be well developed before you recognize them. In some cases, you may not recognize the hypoxia and become impaired to the point of no longer being able to recover on your own.

Transportation

Transportation — Links the transfer of gases from the lungs to their site of production or use in the cells of the body.

Identify the procedures to treat hypoxia in the T-6.

Your first priority when correcting for hypoxia. When using narrow panel pressure demand or diluter demand-type regulators, like those found in the T-6 and the altitude chamber, this is accomplished by placing all three switches in the full-up position. This is known as "gangloading" the regulator. For speed, the procedure should be accomplished with a single sweep of the hand. "Gangloading" the regulator will place it in the On, 100 percent/Max oxygen, emergency pressure setting.