Aerospace Medicine: Physiology at Altitude and the Flight Environment
Core concepts
Aerospace medicine tests how the body behaves when the atmosphere, acceleration, and pressure change faster than physiology can compensate. Master the gas laws (Boyle, Dalton, Henry) because every altitude and pressure question reduces to them. Boyle's law explains trapped-gas expansion in sinus, middle ear, gut, and dental cavities during ascent; Henry's law explains decompression sickness when dissolved nitrogen comes out of solution. Know the oxygen cascade: falling barometric pressure lowers alveolar PO2, so hypoxic hypoxia dominates at altitude even though the fraction of oxygen (21%) is unchanged. Learn the hypoxic ventilatory response, the resulting respiratory alkalosis, and the time course of acclimatization (ventilation, erythropoietin, 2,3-DPG shifts, renal bicarbonate excretion).
Traps in questions
Distinguish hypoxia types: hypoxic (altitude, hypoventilation), stagnant (G-LOC, heart failure), anemic (CO, blood loss), histotoxic (cyanide). Questions love the carbon monoxide trap: pulse oximetry reads falsely normal because carboxyhemoglobin is misread as oxyhemoglobin. Spatial disorientation questions hinge on the somatogravic illusion (false pitch-up sensation during acceleration) and the leans. Decompression sickness versus barotrauma is a frequent discriminator: barotrauma is mechanical pressure injury, DCS is dissolved-gas evolution.
Worked example
A pilot ascends from sea level to 18,000 ft with a sinus cold. The correct answer is barosinusitis (squeeze) from Boyle's law gas expansion/contraction, not DCS, because the mechanism is trapped gas against a blocked ostium.
Rule of thumb
Above 10,000 ft, assume impaired night vision and judgment before symptoms are reported; supplemental oxygen is the first intervention for hypoxic hypoxia.