Description

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

Etiology

• 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)