1. TTTTT T Chapter 4 Flight Physiology EMS 482 Dr. Maha Saud Khalid

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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

8. 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.

9. 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´

10. 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.

11. 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

12. Hypoxia Timeframes (2 of 3)

13. 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

14. 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´.

15. Hypoxic Hypoxia (2 of 2)

16. 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

17. Other Types of Hypoxia (2 of 2)

18. Symptoms of Hypoxia

19. 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´

20. 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

21. 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

22. Four Stages of Hypoxia Related to Altitude (4 of 4)

23. 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.

24. 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

25. 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

26. Primary Stressors of Flight (2 of 9)

27. 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

28. 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

29. Primary Stressors of Flight (5 of 9)

30. 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

31. 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

32. 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

33. 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

34. Human Factors Affect Tolerance to Flight Stressors (1 of 4) IM SAFE = I: Illness M: Medication S: Stress A: Alcohol F: Fatigue E: Emotion

35. 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

36. 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

37. 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

38. 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

39. Disorders Directly Related to Altitude (2 of 3) Decompression sickness – Explained by Henry’s law – Causes circulation problems, death in worst cases

40. Disorders Directly Related to Altitude (3 of 3)