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)