Central nervous dysfunction associated with deep-sea diving.

A group of 23 professional divers was investigated before and after dives to 300 and 350 metres of sea water. 12 divers were also studied during the actual dive. All divers presented neurological symptoms and signs during compression. Intention tremor, ataxia, motor weakness, sensory symptoms, vertigo, nausea and reduced memory were the most prominent features of the High Pressure Nervous Syndrome (HPNS). There were considerable individual differences. Neuropsychological and neurophysiological investigations performed after one dive showed no significant changes in any of the divers, while there was a clear-cut impairment in a group of 6 divers who had performed 2 dives 3 months apart. These changes indicate that there may be pressure-induced brain dysfunction which persists for a transient post-dive period. Loss of short-term memory is a prominent part of this dysfunction. Transitory neurological signs indicating focal cerebral dysfunction were found immediately post-dive in 4 divers, presumably reflecting the unmasking of pre-existing subclinical minimal CNS lesions.