HPNS effects among 18 divers during compression to 360 msw on heliox

Heliox compression beyond 16 ATA may cause EEG changes linked to confusion and somnolence. This condition, known as high pressure neurologic syndrome (HPNS), can include tremor, memory issues, dizziness, nausea, and vomiting. Prior research has shown HPNS effects in controlled environments but lacks detailed data on human divers under operational conditions. No prior work had resolved how HPNS impacts divers during real-world compression to 360 msw. This gap motivated a study to evaluate a specific compression profile. That uncertainty drove the need for repeated neuropsychologic and neurophysiologic testing. It was already known that HPNS symptoms vary among individuals. No prior work had resolved how compression rates and stops influence HPNS severity. This study aimed to address these uncertainties.

The goal was to assess the effects of a specific compression profile on divers compressed to 360 msw using heliox. The study focused on HPNS symptoms and their impact on motor and cognitive functions. The specific problem was whether a progressive compression rate with intermediate stops would reduce HPNS severity. The motivation was to determine if this profile could safely support operational diving. The study aimed to test if mild HPNS effects would still allow acceptable performance. The researchers propose that standard HPNS testing could validate the profile's safety. This study sought to confirm if divers remain functionally capable under such conditions. The aim was to provide evidence for the profile's acceptability in real-world scenarios.

The study involved three dives at NUTEC, each with six different divers compressed to 360 msw on heliox. Neuropsychologic and neurophysiologic tests were conducted repeatedly during compression. The compression profile used progressive rates and included several intermediate stops. HPNS effects were measured using standard testing batteries. The study tracked peripheral motor function, memory, perceptual speed, and reasoning. Postural tremor and EEG power spectrum were also monitored. Data collection occurred at multiple depths to capture changes. The researchers propose that this approach could reliably assess HPNS severity.

Only mild HPNS effects were observed during the compression to 360 msw. Three divers had impairments of more than 2 SD in peripheral motor function. Memory impairment occurred periodically in two divers. Perceptual speed and reasoning were also affected in those two. Fifty percent of divers had postural tremor increases over 2 SD. However, these tremors had minimal impact on motor performance. Six of 18 divers showed EEG changes with alpha band inhibition and theta increase. The most marked performance impairment occurred around 240 msw, while EEG changes occurred deeper than 300 msw. Only one diver showed simultaneous EEG changes, tremor increase, and cognitive impairment.

The study confirms that the compression profile with progressive rates and intermediate stops resulted in mild HPNS effects. Divers remained functionally capable despite HPNS symptoms. The researchers propose that this profile is acceptable for operational use. Standard HPNS testing provided evidence for the profile's safety. No prior work had resolved how HPNS symptoms align with depth-specific changes. The findings suggest that HPNS effects do not necessarily impair divers' performance. The study supports the use of this compression profile in real-world diving scenarios. The authors suggest that further testing could refine HPNS monitoring protocols.