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TTTTT T Chapter 4 Flight Physiology EMS 482 Dr. Maha Saud Khalid
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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
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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
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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
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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)
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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
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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
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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.
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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´
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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.
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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
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Hypoxia Timeframes (2 of 3)
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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
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Hypoxic Hypoxia (1 of 2) Inadequate ventilation or reduction in PO 2 Characterized by lack of oxygen entering blood In air environment, result of reduced atmospheric pressure causing reduced alveolar PaO 2 – Symptoms only begin to manifest at heights above 5,000´.
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Hypoxic Hypoxia (2 of 2)
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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
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Other Types of Hypoxia (2 of 2)
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Symptoms of Hypoxia
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Four Stages of Hypoxia Related 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´
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Four Stages of Hypoxia Related 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
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Four Stages of Hypoxia Related 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
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Four Stages of Hypoxia Related to Altitude (4 of 4)
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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.
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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
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Primary Stressors of Flight (1 of 9) Decreased levels of PO 2 – May quickly cause hypoxia Barometric pressure changes – May require supplemental oxygen – Cause discomfort in air-trapped organs and sinuses
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Primary Stressors of Flight (2 of 9)
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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
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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
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Primary Stressors of Flight (5 of 9)
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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
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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
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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
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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
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Human Factors Affect Tolerance to Flight Stressors (1 of 4) IM SAFE = I: Illness M: Medication S: Stress A: Alcohol F: Fatigue E: Emotion
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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
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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
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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
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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
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Disorders Directly Related to Altitude (2 of 3) Decompression sickness – Explained by Henry’s law – Causes circulation problems, death in worst cases
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Disorders Directly Related to Altitude (3 of 3)
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