Injury resulting from the expansion or contraction of gases in an enclosed space


  • Tissue damage results when a gas-filled space does not equalize its pressure with external pressure
  • Boyle law: At a constant temperature, pressure (P) is inversely related to volume (V):
    • PV = K (constant) or P1V1 = P2V2
    • As pressure increases/decreases, volume decreases/increases
  • Solid- and liquid-filled spaces distribute pressure equally
  • Volume changes are greatest in the few feet nearest the surface
  • Gas-filled cavities in the body are subject to expansion/contraction:
    • External objects:
      • Air pockets in dive suit/mask expand and contract
    • Paranasal sinus:
      • Barotrauma of descent
      • Pressure equalization impaired through nasal ostia resulting in negative pressure in sinus cavity
      • Frontal sinus most commonly affected
    • External ear:
      • Barotrauma of descent
      • Blockage of external auditory canal results in trapped air leading to a vacuum
    • Middle ear:
      • Barotrauma of descent
      • Most common type of barotraumas
      • Seen in 30% of inexperienced divers and 10% of experienced divers
      • Eustachian tube provides sole route of pressure equalization for middle ear
      • Inadequate clearance via eustachian tube leads to increasingly negative pressure gradient across tympanic membrane (TM)
    • Inner ear:
      • Barotrauma of descent
      • Results from rapid development of pressure differential across middle and inner ear (Valsalva, Frenzel maneuvers, rapid descent)
      • Increased pressure in inner ear may cause round or oval window to rupture
      • Frequently associated with middle-ear barotrauma
    • Teeth:
      • Entrapped gas within or around tooth
    • GI:
      • Barotrauma of ascent
      • Swallowed air in GI tract expands as external pressure decreases
    • Pulmonary:
      • Barotrauma of ascent
      • Expansion of gas trapped in lungs (closed glottis, bronchospasm) leads to distention of alveoli
      • Can lead to alveolar rupture
      • Most common is pneumomediastinum
      • Potential arterial gas embolism (AGE) (see “Arterial Gas Embolism”)
      • Divers with decreased lung compliance/increased lung volumes at increased risk (chronic obstructive pulmonary disease [COPD], asthma)

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