Hyperbaric Environments

Hyperbaric Environments - Pressure Points

• Sea level: 1 ATA. Pressure ↑ by 1 ATA per 10m (33 ft) water descent.
  • 10m depth = 2 ATA; 30m depth = 4 ATA.
• Boyle's Law ($P_1V_1 = P_2V_2$): Gas volume inversely proportional to pressure. Affects:
  • Middle ear (barotitis media - commonest)
  • Sinuses (barosinusitis)
  • Lungs (barotrauma on ascent if breath-held)
• Nitrogen Narcosis: Impaired function, euphoria. Starts ~30-40m (4-5 ATA). 📌 Martini's Law.
• Oxygen Toxicity: CNS (seizures), pulmonary. Risk ↑ with $PO_2$ & duration.

⭐ At 30 meters depth (4 ATA), inspired $PN_2$ is ~3.2 ATA, sufficient to cause nitrogen narcosis.

Hyperbaric Environments - Squeeze Play

Barotrauma from pressure differentials during descent (compression). Gas-filled cavities contract if not equalized. Governed by Boyle's Law: $P_1V_1 = P_2V_2$.

• Affected Sites & Manifestations:
  • Middle Ear (most common): Eustachian tube dysfunction. Symptoms: pain, ↓hearing, TM rupture. Prevent: Valsalva.
  • Sinuses: Blocked ostia. Symptoms: facial pain, epistaxis.
  • Lungs (Thoracic Squeeze): Breath-holding descent/extreme depth. Risk: edema, hemorrhage.
  • Mask: Failure to exhale into mask. Result: periorbital petechiae/ecchymosis.
  • Dental (Barodontalgia): Gas in fillings/caries. Pain.
  • GI Tract: Swallowed air expands. in middle ear, sinuses, and mask during diving descent)

⭐ Middle ear barotrauma (otic barotrauma) is the most frequent diving-related medical issue.

Hyperbaric Environments - Bends & Blows

• High pressure (diving) alters gas behavior:

  • Boyle''s Law ($P \propto 1/V$): Barotrauma risk (squeeze/rupture).
  • Henry''s Law (dissolved gas $\propto PP$): N₂ loading at depth.

• At Depth Issues:

  • Nitrogen Narcosis: Impaired function >30m ("Martini''s Law").
  • Oxygen Toxicity: CNS (seizures), pulmonary damage with ↑$PO_2$.

• Ascent Issues (Gas Bubbles):

  • Decompression Sickness (DCS) "Bends": N₂ bubbles from tissues.
    • Type I: Pain (joints), skin, lymphatic.
    • Type II: Neurologic, cardiorespiratory ("chokes"), vestibular ("staggers").
  • Arterial Gas Embolism (AGE) "Blows": Lung barotrauma $\rightarrow$ arterial bubbles. Rapid, severe neuro symptoms.

    ⭐ AGE: Most critical; immediate 100% O₂, recompression. Mimics stroke.

• Prevention/Tx:

  • Slow ascent, decompression stops.
  • 100% O₂, hyperbaric recompression for DCS/AGE.

Hyperbaric Environments - Healing Breaths

• Hyperbaric Oxygen Therapy (HBOT): Inhaling 100% O₂ at >1 Atmosphere Absolute (ATA), typically 2-3 ATA.
• Mechanism:
  • ↑ Plasma dissolved O₂ (Henry's Law: $P = kC$).
  • Vasoconstriction (↓edema).
  • Angiogenesis, fibroblast proliferation.
  • Bactericidal/bacteriostatic.
• Key Indications:
  • Decompression Sickness (DCS), Air/Gas Embolism.
  • CO Poisoning.
  • Clostridial Myonecrosis (Gas Gangrene).
  • Problem Wounds (diabetic ulcers).
  • Radiation Necrosis.
• Oxygen Toxicity:
  • CNS: Seizures (Paul Bert effect); ⚠️ risk ↑ >2 ATA.
  • Pulmonary: Inflammation, fibrosis (Lorrain Smith).
  • Ocular: Myopia, cataracts.
  • Barotrauma (ears, sinuses).

⭐ HBOT significantly reduces the half-life of carboxyhemoglobin (COHb) in CO poisoning, from ~320 min on room air to ~20-30 min with 100% O₂ at 3 ATA.

High‑Yield Points - ⚡ Biggest Takeaways

• Boyle's Law (gas volume inversely to pressure) explains barotrauma risk.
• Nitrogen narcosis impairs function at depths >30m (↑dissolved N₂).
• Oxygen toxicity causes CNS seizures or pulmonary damage.
• Decompression Sickness (DCS) results from N₂ bubbles due to rapid ascent.
• Arterial Gas Embolism (AGE): severe risk from pulmonary barotrauma during ascent.
• HBOT: 100% O₂ at >1 ATA for CO poisoning, DCS, problem wounds.