Effects of nitrogen and helium on CNS oxygen toxicity in the rat

• Published in: Journal of applied physiology (1985) 2005-01, Vol.98 (1), p.144-150
• Main Authors: Arieli, R, Ertracht, O, Oster, I, Vitenstein, A, Adir, Y
• Format: Article
• Language: English
• Subjects: Administration, Inhalation; Animals; Applied physiology; Biological and medical sciences; Brain - drug effects; Brain - physiopathology; Chemical and industrial products toxicology. Toxic occupational diseases; Dose-Response Relationship, Drug; Drug Combinations; Electromyography - methods; Evoked Potentials - drug effects; Gas, fumes; Helium; Helium - administration & dosage; Helium - adverse effects; Human physiology applied to population studies and life conditions. Human ecophysiology; Hyperbaric Oxygenation - adverse effects; Inert Gas Narcosis - physiopathology; Male; Medical sciences; Nervous system; Nitrogen; Nitrogen - administration & dosage; Nitrogen - adverse effects; Oxygen - administration & dosage; Oxygen - adverse effects; Rats; Rats, Sprague-Dawley; Rodents; Toxicity; Toxicology; Transports. Aerospace. Diving. Altitude
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00506.2004

Israel Naval Medical Institute, Israel Defense Forces Medical Corps, Haifa 31080, Israel Submitted 12 May 2004 ; accepted in final form 13 August 2004 The contribution of inert gases to the risk of central nervous system (CNS) oxygen toxicity is a matter of controversy. Therefore, diving regulations apply strict rules regarding permissible oxygen pressures (P O 2 ). We studied the effects of nitrogen and helium (0, 15, 25, 40, 50, and 60%) and different levels of P O 2 (507, 557, 608, and 658 kPa) on the latency to the first electrical discharge (FED) in the EEG in rats, with repeated measurements in each animal. Latency as a function of the nitrogen pressure was not homogeneous for each rat. The prolongation of latency observed in some rats at certain nitrogen pressures, mostly in the range 100 to 500 kPa, was superimposed on the general trend for a reduction in latency as nitrogen pressure increased. This pattern was an individual trait. In contrast with nitrogen, no prolongation of latency to CNS oxygen toxicity was observed with helium, where an increase in helium pressure caused a reduction in latency. This bimodal response and the variation in the response between rats, together with a possible effect of ambient temperature on metabolic rate, may explain the conflicting findings reported in the literature. The difference between the two inert gases may be related to the difference in the narcotic effect of nitrogen. Proof through further research of a correlation between individual sensitivity to nitrogen narcosis and protection by N 2 against CNS oxygen toxicity in rat may lead to a personal O 2 limit in mixed-gas diving based on the diver sensitivity to N 2 narcosis. hyperbaric oxygen; electroencephalogram; nitrogen narcosis; inert gas; diving Address for reprint requests and other correspondence: R. Arieli, Israel Naval Medical Institute, POB 8040, Haifa 31080, Israel (E-mail: rarieli{at}netvision.net.il )