Diving Physiology and Barotrauma: Core Concepts
Pressure and gas laws
Absolute pressure is the foundation. At sea level it is 1 atm; in seawater add 1 atm per 10 m, so 30 m equals 4 ATA. Boyle law links depth to gas volume and explains middle-ear, sinus, pulmonary, and mask barotrauma. Henry law links partial pressure to dissolved inert gas; nitrogen uptake depends on depth, time, and tissue perfusion. Haldane-style models track tissue compartments and supersaturation. Bubbles cause decompression sickness (DCS), while alveolar gas entering the circulation causes arterial gas embolism (AGE).
Clinical distinctions and traps
DCS often begins after surfacing, sometimes with delay, causing joint pain, paresthesia, vertigo, or cardiorespiratory symptoms. AGE usually occurs within minutes of surfacing and may present with stroke-like findings or sudden collapse. Questions frequently test the undeserved DCS concept, flying after diving, altitude exposure, and the difference between nitrogen narcosis and oxygen toxicity. Narcosis impairs judgment and performance at depth and resolves with ascent; oxygen toxicity causes CNS seizures or pulmonary symptoms and depends on PO2 and exposure time. A normal examination does not exclude patent foramen ovale or inner-ear barotrauma.
Worked example and rule of thumb
A 6 L balloon at the surface taken to 30 m (4 ATA) is compressed to 1.5 L; returned to the surface, it returns to 6 L if no gas is lost. Rule of thumb: seawater absolute pressure equals depth in meters divided by 10, plus 1. Use pressure ratios, not gauge pressure, for gas-volume questions.