PHYSICAL CHARACTERISTICS OF AN ENCLOSED AFFERENT RESERVOIR BREATHING SYSTEM

We have assessed the characteristics of the Ohmeda EnclosedAfferent Reservoir Breathing System (EAR) using simulated spontaneousventilation and controlled ventilation. The additional workof breathing through the system was measured and shown to becomparable to that of a modified Mapleson D breathing system(Bain) for fresh gas flows producing similar end-tidal carbondioxide concentrations. It was shown under conditions of simulatedcontrolled ventilation that end-tidal gas concentration wasrelatively insensitive to variations in inspired to expiredratio (I:E), tidal volume (VT) and deadspace (VD). Measurementof the volume of carbon dioxide rebreathed using simulated spontaneousventilation led to the prediction that rebreathing of carbondioxide would begin to occur in the EAR when fresh gas flowto total ventilation ratio (VF: VE) was approximately 0.87.However, comparison of the results of model lung tests and clinicaldata suggests that great caution should be taken in extrapolatingsuch results into clinical advice.