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

Abstract

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. 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. 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. 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.