Understanding the "Underwater" Sound During HBOT
The sensation of hearing people talk underwater during hyperbaric oxygen therapy is caused by pressure-related changes in the middle ear and eustachian tube function, which temporarily alter sound transmission through the conductive hearing apparatus while you're in the pressurized chamber 1.
Physiological Mechanism
The primary cause is middle ear pressure equalization challenges during compression and decompression phases of HBOT. Here's what happens:
Pressure differential effects: As the hyperbaric chamber pressurizes to >1 atmosphere absolute (typically 2.0-2.8 ATA for sudden hearing loss treatment), your middle ear must equalize pressure through the eustachian tube 1, 2, 3.
Eustachian tube dysfunction: During HBOT sessions, approximately 17-45% of patients experience difficulty equalizing middle ear pressure, which creates a temporary conductive hearing impairment 1.
Fluid accumulation: The pressure changes can cause transient middle ear effusion or mucosal edema, which dampens sound transmission through the ossicular chain—creating that characteristic "underwater" or muffled quality 1.
Why This Happens Specifically During HBOT
Rapid pressure changes: Unlike gradual altitude changes, HBOT involves relatively rapid compression (typically over 10-15 minutes to reach treatment pressure), which challenges the eustachian tube's ability to equilibrate 1, 2.
Sustained high pressure: You're maintained at elevated pressure for 30-90 minutes per session, during which the middle ear must remain equilibrated 2, 3.
Decompression phase: The return to normal pressure can also create temporary negative middle ear pressure if equalization is incomplete 1.
Clinical Significance
This sensation is generally benign and temporary, resolving after the session ends, though you should monitor for:
Middle ear barotrauma: Occurs in approximately 6.25% of SSNHL patients receiving HBOT, though concurrent steroid use (which you're likely receiving) reduces this risk 1, 2.
Persistent symptoms: If the underwater sensation persists between sessions or worsens, notify your hyperbaric medicine team, as this may indicate developing barotrauma requiring intervention 1.
Practical Considerations
Active equalization techniques: Performing Valsalva maneuvers or swallowing during compression/decompression helps minimize the sensation 1.
Not a contraindication: This sensation alone doesn't indicate treatment failure or need to discontinue HBOT, especially since you're within the optimal 2-week treatment window for sudden hearing loss 1, 2.
Distinguish from your underlying condition: The temporary muffled hearing during HBOT is mechanically different from your sensorineural hearing loss, which involves cochlear ischemia that HBOT is designed to treat 1, 2.