The effects of various gases on cortical and spinal somatosensory evoked potentials at pressures up to 10 bar.

The development of dog electrophysiological models for studying the treatment of cerebral arterial air embolism and spinal cord decompression sickness, required that the effects of the treatment gases on spinal and cortical somatosensory evoked potentials (SEP and CEP) be known. We found an inverse linear relationship between CEP amplitude and air pressure to 230 ft. An asymptote was approached when pressure was increased to 300 ft. This effect was not seen with 20% oxy-helium. The waves representing local cord events were depressed to a lesser extent than were the CEPs. We were able to detect an equilibration time in the EP suppression comparable to estimated inert gas wash-in time for the brain. A small depression of CEPs that did not reach significance was seen with exposure to 2.8 bar of oxygen and continuous exposure for up to 120 min caused no further diminution in amplitude than would be caused by time alone.