Forty commercial saturation divers, mean age 34-9 (range 24-49) years, were examined one to seven years after their last deep dive (190-

A group of 70 professional divers and 47 healthy control subjects who had never dived were examined with magnetic resonance (MR) imaging to determine the prevalence of focal white matter changes in the brain. Spots of high signal intensity in white matter on proton density- and/or T2-weighted spin-echo images were detected in 42% of the control subjects and in 34% of the divers. In the control subjects, the prevalence of more than three changes was related to smoking, use of alcohol, head trauma, age of more than 35 years, and a combination of several cerebrovascular risk factors. This relationship was not present in the divers. The prevalence of changes in divers was inversely related to diving depth, amount of diving, participation in "unsafe diving," and decompression sickness. The reasons for these results could not be ascertained. The results are compared with those of MR imaging studies of white matter changes recently presented by other research groups.

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Eighteen divers performed a simulated dive to a depth of 360 metres of seawater breathing a mixture of helium and oxygen. Clinical neurological examinations and neurophysiological tests were performed before and after the dives. Two divers had mild ataxic signs and changed electronystagmography after the dive, and one had impaired vibration sense in one lower extremity. Abnormal EEGs with slow waves and sharp potentials, seen primarily in the temporal regions, occurred in 2 divers. No changes were found in the magnetic resonance imaging brain scans. The divers with evidence of previous central nervous system injury, or a history of unconsciousness or previous decompression sickness seemed more likely to develop neurological signs after these deep dives. This study shows that deep diving may induce immediate neurological changes. We recommend that future deep divers have a neurological examination and 2 separate EEGs included in their medical examinations.