Flight Physiology Basics
The Atmosphere
Standard Atmosphere (ISA) assumes:
- Pressure: 1013.25 hPa at MSL, decreasing with altitude.
- Temperature: +15°C at MSL, decreasing by 2°C/1000 ft (1.98°C) up to the Tropopause (36,090 ft).
- Composition: 78% Nitrogen, 21% Oxygen, 1% other gases. (Constant up to ~70,000 ft).
Gas Laws
- Boyle's Law ($P_1 V_1 = P_2 V_2$): Pressure and volume are inversely proportional.
- Relevance: Trapped gases expand on ascent (ears, sinuses, teeth, stomach, intestine).
- Dalton's Law ($P_{Total} = P_1 + P_2 + ...$): Total pressure is the sum of partial pressures.
- Relevance: As altitude increases, total pressure drops, so the partial pressure of oxygen ($ppO_2$) drops, leading to Hypoxia.
- Henry's Law: The amount of gas dissolved in a liquid is proportional to its partial pressure.
- Relevance: Decompression Sickness (DCS). Nitrogen bubbles form in blood when pressure drops rapidly (Scuba diving + Flying).
Hypoxia
A state of oxygen deficiency in the body.
- Hypoxic Hypoxia: Insufficient oxygen in the air (Altitude).
- Anemic Hypoxia: Blood cannot carry oxygen (CO Poisoning, Smoking reduces hemoglobin efficiency).
- Stagnant Hypoxia: Blood not moving (G-forces, Heart failure, Cold).
- Histotoxic Hypoxia: Cells cannot use oxygen (Alcohol, Cyanide).
Symptoms: Euphoria, cyanosis (blue lips/fingernails), impaired judgment, tunnel vision. Time of Useful Consciousness (TUC): Decreases rapidly with altitude (e.g., FL300: 1-2 mins; FL400: 15-20 secs).
Hyperventilation
Over-breathing usually caused by stress/anxiety.
- Effect: Flushes too much CO2 from the blood (Hypocapnia). Blood becomes alkaline.
- Symptoms: Dizziness, tingling in hands/feet, visual tunneling (similar to hypoxia).
- Action: Slow breathing rate.