The Effect of Acute Exposure to Hyperbaric Oxygen on Respiratory System Mechanics in the Rat

Purpose This study was designed to investigate the possibleeffects of acute hyperbaric hyperoxia on respiratorymechanics of anaesthetised, positive-pressure ventilatedrats.Methods We measured respiratory mechanics by the endinflationocclusion method in nine rats previously acutelyexposed to hyperbaric hyperoxia in a standard fashion. Themethod allows the measurements of respiratory systemelastance and of both the ‘‘ohmic’’ and of the viscoelasticcomponents of airway resistance, which respectivelydepend on the newtonian pressure dissipation due to theohmic airway resistance to air flow, and on the viscoelasticpressure dissipation caused by respiratory system tissuesstress–relaxation. The activities of inducible and endothelialNO-synthase in the lung’s tissues (iNOS and eNOSrespectively) also were investigated. Data were comparedwith those obtained in control animals.Results We found that the exposure to hyperbarichyperoxia increased respiratory system elastance and boththe ‘‘ohmic’’ and viscoelastic components of inspiratoryresistances. These changes were accompanied by increasediNOS but not eNOS activities.Conclusions Hyperbaric hyperoxia was shown to acutelyinduce detrimental effects on respiratory mechanics. Apossible causative role was suggested for increased nitrogenreactive species production because of increased iNOSactivity.