Modeling pulmonary and CNS O2 toxicity and estimation of parameters for humans

Abstract

10.1152/japplphysiol.00434.2001.—The power expression for cumulative oxygen toxicity and the exponential recovery were successfully applied to various features of oxygen toxicity. From the basic equation, we derived expressions for a protocol in which Po 2 changes with time. The parameters of the power equation were solved by using nonlinear regression for the reduction in vital capacity (ΔVC) in humans:  %ΔVC  = 0.0082 × t 2(Po 2/101.3)4.57, where t is the time in hours and Po 2is expressed in kPa. The recovery of lung volume is  ΔVC t  = ΔVCe × e −(−0.42 + 0.00379Po 2 ) t , where ΔVC t is the value at time tof the recovery, ΔVCe is the value at the end of the hyperoxic exposure, and Po 2 is the prerecovery oxygen pressure. Data from different experiments on central nervous system (CNS) oxygen toxicity in humans in the hyperbaric chamber ( n = 661) were analyzed along with data from actual closed-circuit oxygen diving ( n = 2,039) by using a maximum likelihood method. The parameters of the model were solved for the combined data, yielding the power equation for active diving: K = t 2(Po 2/101.3)6.8, where tis in minutes. It is suggested that the risk of CNS oxygen toxicity in diving can be derived from the calculated parameter of the normal distribution: Z = [ln( t) − 9.63 +3.38 × ln(Po 2/101.3)]/2.02. The recovery time constant for CNS oxygen toxicity was calculated from the value obtained for the rat, taking into account the effect of body mass, and yielded the recovery equation: Kt = K e × e −0.079 t , where Kt and K e are the values of K at time t of the recovery process and at the end of the hyperbaric oxygen exposure, respectively, and tis in minutes.