Human brainstem auditory-evoked potentials in deep experimental diving to pressures up to 62.5 bar

Area of Science:

• Neuroscience
• Diving Physiology
• High-Pressure Biology

Background:

• High Pressure Neurologic Syndrome (HPNS) limits human diving capabilities.
• The precise neural mechanisms of HPNS remain incompletely understood.
• Brainstem Auditory-Evoked Potentials (BAEP) offer a method to investigate neural function under pressure.

Purpose of the Study:

• To elucidate the neural underpinnings of HPNS.
• To assess the impact of compression rates and acclimation on HPNS.
• To investigate changes in auditory pathway function during deep dives.

Main Methods:

• Recorded BAEP in divers during two experimental chamber dives (Titan VIII and Titan XI) to depths up to 615 msw.
• Monitored for clinical HPNS symptoms, including vestibular disturbances and tremor.
• Analyzed latency and amplitude changes in BAEP components, particularly the IV/V complex.

Main Results:

• Prolongation of the IV/V complex in BAEP was observed at 525 msw during rapid compression (Titan VIII).
• Clinical signs and IV/V delay diminished with extended acclimation at depth (Titan XI) and slower compression.
• Absence of significant changes in Wave I and Wave III latency suggests suppression of pontomesencephalic transmission.

Conclusions:

• HPNS symptoms and BAEP alterations are influenced by compression rates and acclimation time.
• Pressure appears to suppress synaptic transmission or enhance inhibitory modulation within the auditory pathway.
• No persistent BAEP changes were noted post-dive, indicating reversible effects.