Steady-state minute volume determination by body-only plethysmography in juvenile rhesus monkeys

When one is using nonhuman primates for studying the inhalation of infective or toxic agents, a respiratory minute volume (MV) range of +/- 50 ml is desirable to ensure the accurate delivery of calculated doses of the aerosolized agent. When one is working with highly infective or toxic agents, it is desirable to anesthetize the animals and to separate the plethysmograph, used to measure MV, from the aerosol chamber, used to administer agents, in order to minimize decontamination procedures and to maximize safety. In our laboratory the sequential completion of these procedures requires at least 20 min. Therefore it is necessary to find an anesthetic that achieves a +/- 50 ml steady-state MV for at least 20 min and that does not change when an animal is transported from one apparatus to another. Using 2.6- to 4.0-kg, 14- to 18-month-old rhesus macaques, we determined that tiletamine/zolazepam induced a steady-state MV of 48 +/- 17.8 min, beginning 21.5 +/- 4.7 min after injection of the anesthetic agent. This MV did not significantly change when animals were transported. The use of ketamine and ketamine/acepromazine resulted in a steady-state MV period of 11.5 +/- 4.5 and 22.0 +/- 7.9 min respectively. When we compared these findings with previously reported mathematical estimations of MV based on functions of weight or respiratory rate, we further determined that the accurate measurement of MV before each aerosol exposure was critical for calculating inhaled doses of the agent.