Modification of an infant incubator for exposure of experimental animals to nitrous oxide

Research with N2O is hampered because it is a gas and must be inhaled by the test subject rather than injected. Described herein is the development of a practical and efficient exposure chamber for such research. A Model C-35 Isolette infant incubator was modified by installation of a manifold system for distribution and opposed-suction fans for a circulation of the gas mixture (N2O in oxygen). An exponential model was developed, predicated on gas concentration uniformity, to track the increasing concentration of N2O during chamber filling and to predict the time required for the chamber to assume a steady-state level of N2O. This model requires that three things be known: the volumetric flow rate of administered gas mixture, the concentration of N2O in that mixture, and the volume of the chamber. The model predicts that X(t)/X infinity = 1 - exp(-t/tau), where X(t) is the concentration of N2O of an instant t; X infinity, the concentration of N2O administered; and tau, the time constant--the ratio of chamber volume to volumetric flow rate. This model was confirmed via mass spectroscopy analysis of gas from the chamber during filling.