Susceptibility of the Inner Ear Structure to Shunt-related Decompression Sickness

Introduction: Decompression sickness (DCS) is caused by formation and growth of bubbles from excess dissolved gas in body tissues following reduction in ambient pressure. Inner ear decompression sickness (IEDCS) is a complex disorder involving the vestibulo-cochlear apparatus whose pathophysiology remains incompletely understood.

Methods: The records of 662 consecutive DCS cases treated over a 7-yr period at 2 UK hyperbaric units were examined for symptoms suggesting IEDCS (nausea, vomiting, dizziness, and hearing loss arising within 2 h of surfacing). For IEDCS cases, demographics, dive, treatment, and outcome data were extracted with particular attention to the outcome of testing for a right-to-left shunt.

Results: Included were 31 men and 2 women with a mean age of 46 yr (range 31-61 yr). Of these, 16 patients had isolated IEDCS and 17 patients had associated symptoms ranging from joint pain to tingling and numbness. The depth of the dive leading to the incident ranged from 49-256 ft (15-78 m). As primary treatment, 21 patients received a U.S. Navy Treatment Table 6 (USN TT6) and 11 patients received a Comex 30. No difference in the speed of recovery or number of treatments needed was seen between the two tables. All patients were advised to have a right to left shunt (RLS) check, but only 30 complied with that, with 24 (80%) testing RLS positive.

Conclusion: Our retrospective study confirms the correlation between IEDCS and the presence of a significant patent foramen ovale (PFO). In our series 48% of patients had an isolated IEDCS. IEDCS responds slowly to treatment irrespective of the initial table used. Recovery is thought to be mainly a central compensation process.