Extended lifetimes of bubbles at hyperbaric pressure may contribute to inner ear decompression sickness during saturation diving.

Inner ear decompression sickness (IEDCS) may occur after upward or downward excursions in saturation diving. Previous studies in nonsaturation diving strongly suggest that IEDCS is caused by arterialization of small venous bubbles across intracardiac or intrapulmonary right-to-left shunts and bubble growth through inward diffusion of supersaturated gas when they arrive in the inner ear. The present study used published saturation diving data and models of inner ear inert gas kinetics and bubble dynamics in arterial conditions to assess whether IEDCS after saturation excursions could also be explained by arterialization of venous bubbles and whether such bubbles might survive longer and be more likely to reach the inner ear under deep saturation diving conditions. Previous data show that saturation excursions produce venous bubbles. Modeling shows that gas supersaturation in the inner ear persists longer than in the brain after such excursions, explaining why the inner ear would be more vulnerable to injury by arriving bubbles. Estimated survival of arterialized bubbles is significantly prolonged at high ambient pressure such that bubbles large enough to be filtered by pulmonary capillaries but able to cross right-to-left shunts are more likely to survive transit to the inner ear than at the surface. IEDCS after saturation excursions is plausibly caused by arterialization of venous bubbles whose prolonged arterial survival at deep depths suggests that larger bubbles in greater numbers reach the inner ear. NEW & NOTEWORTHY Inner ear decompression sickness that occurs during deep saturation diving is explained by arterialization of venous bubbles across intracardiac or intrapulmonary right-to-left shunts and growth of these bubbles if they arrive in the inner ear. Bubbles in arterial blood have prolonged lifetimes at hyperbaric pressures compared with at sea level. This can explain why inner ear decompression sickness is more characteristic of rapid decompressions at great depths than of decompression at sea level.