Post on 08-Jan-2018
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TTTTT TChapter 4
Flight Physiology
EMS 482
Dr. Maha Saud Khalid
Barometric Maladies
• Flight physiology requires recognition that: –Many conditions are exacerbated by changes in
barometric pressure– Forces experienced during flight can significantly
impact disease pathophysiology
Atmospheric Composition (1 of 3)
• Percentage of gases constitutes almost 99% of the atmosphere– Remains constant, but density varies with altitude
• Oxygen – 21% of atmosphere, regardless of altitude– By product of photosynthesis– Necessary to sustain life
Atmospheric Composition (2 of 3)
• Nitrogen– 78% of total volume of atmosphere– Most abundant gas– Inert, odorless, colorless, tasteless– Critical element for life
• Argon – 0.93% of atmosphere
Boyle’s Law (1 of 3)
• When volume of gas increases, pressure decreases; when volume of gas decreases, pressure increases.
• “Boil Very Prudently” – Boyle = Volume (Very) x Pressure (Prudently)
Boyle’s Law (2 of 3)
• Numerous implications found in aviation medicine – Tension pneumothorax, pneumocephalus, sinus pain
• Affects certain types of medical equipment– Endotracheal tubes, IV fluids, PASGs, nasogastric and
orogastric tubes
Charles’ Law
• As air heats up, volume increases, allowing molecules to spread out, making air less dense.– Helicopters fly better in cold weather.
• “Charles’ cold,” “Charles Celsius” • Significant in flight medicine because aircraft
cabins get cold at altitude– Hypothermia
Dalton’s Law (1 of 2)
• In gas mixture, gas molecules are unaffected by each others’ motion because of space between molecules.– Increasing altitude results in proportional decrease of
partial pressures of gases found in atmosphere.• “Dalton’s gang” • Decrease in pressure can cause hypoxia.
Hypoxia
• Main aviation hazard, with potential for catastrophic results– 8–10 incidents occur during flight every year.– Most caused by cabin pressure failure
• May occur in otherwise healthy people at altitudes less than 10,000´
Early Signs of Hypoxia
• Impaired judgment – Limits aviator’s ability to recognize condition or take
immediate corrective actions• Fatigue and hypoglycemia– Make hypoxia difficult to recognize– Fatigue and hunger also contribute to hypoxia.
Hypoxia Timeframes (1 of 3)
• Effective performance time – Limited timeframe during which person can function with
inadequate level of oxygen• Time of useful consciousness– Period between sudden oxygen deprivation at given
altitude and onset of physical, mental impairment to point at which deliberate function is lost
Hypoxia Timeframes (2 of 3)
Hypoxia Timeframes (3 of 3)
• Vary by individual depending on:– Individual tolerances– Method of hypoxia induction– Environment before hypoxia– Amount of exercise person undertakes– Percentage of oxygen prior to hypoxia – Rapid cabin depressurization
Hypoxic Hypoxia (1 of 2)
• Inadequate ventilation or reduction in PO2 • Characterized by lack of oxygen entering blood• In air environment, result of reduced atmospheric
pressure causing reduced alveolar PaO2
– Symptoms only begin to manifest at heights above 5,000´.
Hypoxic Hypoxia (2 of 2)
Other Types of Hypoxia (1 of 2)
• Histotoxic hypoxia– Cell’s inability to use oxygen adequately
• Stagnant hypoxia – Failure to transport oxygenated blood
• Hypemic hypoxia (anemic hypoxia)– Reduction in ability of blood to carry oxygen to tissues,
despite oxygen’s abundance
Other Types of Hypoxia (2 of 2)
Symptoms of Hypoxia
Four Stages of HypoxiaRelated to Altitude (1 of 4)
• Indifferent stage– Minor physiological effects– Experienced between sea level and 10,000´
• Compensatory stage– Body provides short-term compensation against hypoxia
effects– Experienced between 10,000´ and 15,000´
Four Stages of HypoxiaRelated to Altitude (2 of 4)
• Disturbance stage– Characterized by subjective, objective hypoxia symptoms– Cognition impairment most critical– Experienced between 15,000´ and 20,000´– Personality manifestations– Muscular coordination decreases
Four Stages of HypoxiaRelated to Altitude (3 of 4)
• Critical stage– Occurs within 3–5 minutes– Mental confusion, quickly followed by incapacitation,
unconsciousness, death– Experienced between 20,000´ and above– Hyperventilation
Four Stages of HypoxiaRelated to Altitude (4 of 4)
Hypoxia Treatment
• Supply 100% oxygen for complete restoration of function (hypoxia paradox).
• Avoid hypoxia.– Use supplemental oxygen.– Descend to below 10,000´ if hypoxia is detected.
Supplemental Oxygen Requirements
• FAR Part 135.89 – Governs use of supplemental oxygen by pilots – Provides rules for pressurized, nonpressurized aircraft
• FAR Part 91.211– Requires passengers be provided with supplemental
oxygen
Primary Stressors of Flight (1 of 9)
• Decreased levels of PO2 – May quickly cause hypoxia
• Barometric pressure changes– May require supplemental oxygen– Cause discomfort in air-trapped organs and sinuses
Primary Stressors of Flight (2 of 9)
Primary Stressors of Flight (3 of 9)
• Thermal changes (heat and cold)– Increase oxygen demands on body– Cause hypothermia (higher altitudes) or heat stress
(ambient temperature changes)• Vibration from aircraft– Causes discomfort, chest/abdominal pain, decreased vision,
fatigue
Primary Stressors of Flight (4 of 9)
• Decreased humidity– More common in jet aircraft– Causes dryness, dehydration, jet-lag– Requires hydration of patients, crew
• Noise– Causes variety of problems, including increased blood
pressure, headaches, stomach ulcers, apathy, hearing loss
Primary Stressors of Flight (5 of 9)
Primary Stressors of Flight (6 of 9)
• Fatigue– Caused by physiologic problems encountered in
flight environment– Leads to delayed reaction time, vulnerability to
critical errors• Gravitational forces– May lead to hypoxia, rashes, organ displacement,
loss of consciousness, other symptoms
Primary Stressors of Flight (7 of 9)
• Spatial disorientation and illusions of flight – Incorrect understanding of body’s position
with respect to earth– Causes disorientation, errors
• Third spacing– Loss of fluids from intravascular space
into tissues– Hypovolemia, potentiating hypoxia
Primary Stressors of Flight (8 of 9)
• Flicker vertigo – Caused by exposure to low-frequency flickering or
flashing of bright light – Effects include nausea, vomiting, seizures
• Fuel vapors– May cause headaches, nausea
• Weather– Poor weather conditions or need to use IFRs
increases stress
Primary Stressors of Flight (9 of 9)
• Anxiety– Caused by claustrophobia, frustration over space
limitations, fear – Patients may experience, too
• Night flying– Causes disadvantages like limited field of vision, loss of
depth perception, monochromatic vision, reduced sense of speed
Human Factors Affect Tolerance to Flight Stressors (1 of 4)
IM SAFE =I: IllnessM: MedicationS: StressA: AlcoholF: FatigueE: Emotion
Human Factors Affect Tolerance to Flight Stressors (2 of 4)
• Illnesses, like common cold, may cause:– Severe headaches, vertigo, nausea
• Medications affect tolerance to hypoxia.– Follow FAA list of approved prescription, OTC
medications • Stress can lead to distraction and poor judgment
Human Factors Affect Tolerance to Flight Stressors (3 of 4)
• Alcohol can cause:– Poor judgment, histotoxic hypoxia, hangover
symptoms– Review FAR Part 91
• Fatigue may cause:– Judgment errors, narrowed attention,
uncharacteristic behavior, accidents
Human Factors Affect Tolerance to Flight Stressors (4 of 4)
• Emotionally upsetting events can:– Impair judgment
• Additional stressors– Smoking– Poor diet/obesity– Age– Physical exertion during flight
Disorders Directly Related to Altitude (1 of 3)
• Barotrauma may cause pain in the:– Digestive tract, sinuses, teeth, middle ear, lungs
• Dysbarism– Causes pain in closed cavities
• Barotitis media – Causes pain in middle ear, eardrum rupture
Disorders Directly Related to Altitude (2 of 3)
• Decompression sickness – Explained by Henry’s law– Causes circulation problems, death in worst cases
Disorders Directly Related to Altitude (3 of 3)