Responses of retinal and visual pathway potentials of the guinea pig to nitrogen and helium at high pressure.

Electroretinographic, optic chiasm, and visual cortex potentials were monitored in the awake guinea pig as nitrogen pressures were raised to 16 ATA and held for 30 min. Pressurization to 90 ATA with helium in 10-ATA increments followed. We sought to (a) quantify the depressant effect of nitrogen on the retina as compared to the central visual pathway, and (b) to test for pressure reversibility. The electroretinogram was reduced approximately 15%, the chiasm potential by 15%, and the cortical response by 32% in 16 ATA nitrogen, and latent periods for the three signals increased an average of 5-8%. Helium at pressure did not restore the amplitude of the electroretinogram or optic chiasm response, but the visual cortex potential returned to control levels near 90 ATA total pressure. Reversal of the nitrogen-induced latency increases by helium was partially effective up to 40 ATA. Control latent periods were not reached. Further attenuation of the electroretinogram and chiasm response amplitudes, and increased latencies of all signals were observed at 50-90 ATA.