title: Recovery time constant in central nervous system O2 toxicity in the rat.
abstract: The development of oxygen toxicity can be delayed by intermittent periods of normoxia. However, there is no accepted procedure for quantifing the recovery during normoxia. A cumulative oxygen toxicity index - K, when K reaches a critical value (Kc) and the toxic effect is manifested, can be calculated using the equation K = t(2)e x PO(2)c where t(e) is hyperoxic exposure time and PO2 is oxygen pressure and c is a power parameter. Recovery during normoxia (reducing K) is calculated by the equation K2 = K1 x e(-rt(r)) where t(r) is recovery time, r being the recovery time constant. A combination of accumulation of oxygen toxicity and its recovery can be used to calculate central nervous system oxygen toxicity. In protocol A (n = 25), r was calculated for rats exposed either continuously to 608 kPa oxygen or to PO2 = 608 kPa followed by a period of normoxia (3.5% O2), with a subsequent return to PO2 = 608 kPa until appearance of the first electrical discharge (FED) in the electroencephalogram which precedes clinical convulsions. In protocol B (n = 22), predicted latency to the FED was compared to measured latency for seven different exposures to hyperbaric oxygen (HBO), followed by a period of normoxia and further HBO exposure. Recovery followed an exponential path, with r = 0.31 (SD 0.12) min(-1). The predicted latency to FED in protocol B correlated with the measured latencies. Calculation of the recovery of the CNS oxygen toxicity agreed with the previously suggested exponential recovery of the hypoxic ventilatory response and was probably a general recovery process. We concluded that recovery can be applied to the design of various hyperoxic exposures.
authors.affiliation: Israel Naval Medical Institute, IDF Medical Corps, Haifa, Israel.
authors.forename: R
authors.initials: R
authors.lastname: Arieli
authors.forename: A
authors.initials: A
authors.lastname: Gutterman
mesh_terms: D000818:Animals; D002490:Central Nervous System / Q000187:drug effects*; D008297:Male; D010100:Oxygen / Q000633:toxicity*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010100:Oxygen