A new appraisal of high pressure nervous syndrome

The principal symptoms of High Pressure Nervous Syndrome (HPNS) were described for Man in 1969. Results obtained since then, for monkeys as well as for Man, have shown that while these original observations remain valid, they must be slightly revised. Firstly, all the symptoms of HPNS do not obey the same laws. Secondly, the gravity of HPNS does not depend only on the depth attained. The symptoms depend on the gas mixture used and, for a given gas mixture at a given depth, on the rate and mode of compression. It is possible to reduce the gravity of HPNS by using a specific mode of compression. However, it should be noted that the disappearance of a given symptom due to the modification of one or several parameters of the compression, does not necessarily signify the disappearance of HPNS. Experiments are still necessary to evaluate the most significant alarm signals for each type of compression used.