An Automated Basal Metabolism Apparatus for Small Animals. ∗

Various devices have been described for determining the basal metabolic rate (BMR) of small animals(1,2,5). However, except for one complex apparatus(l), none of these allow the investigator to eliminate periods of stimulated oxygen consumption due to physical activity of the animal from the determination of the BMR. The system to be described allows for the detection, and therefore the elimination from the BMR calculation the increased oxygen consumption periods due to physical activity as well as other factors which influence this measurement. This apparatus automatically records oxygen consumption, respiratory rate and physical activity using equipment which is readily available in many laboratories. The method is based on the principle that oxygen consumption is proportional to the decrease in pressure in a closed system(2). An equilibration device returns the internal pressure to atmospheric at approximately one-minute intervals. By employing electronic transduction and amplification as well as a multichannel recorder, a highly sensitive system has been developed which simultaneously records oxygen consumption of 3 animals. No temperature controlling device was employed since it was found that no detectable change in temperature occurred during the short measurement period when the animals were inactive.

Description of apparatus. The system consists of 3 identical units, one of which is shown diagrammatically in Fig. 1. The rat is placed in a 4.8 liter desiccator in a wire mesh holder over 200 g of soda lime which serves as a carbon dioxide absorbant. The desiccator is connected to both a transducer and a stopcock by way of rubber tubing and a glass “T” tube. The transducer is in turn connected to the amplifier and the oscillograph. The stopcok is spring-loaded to hold it in a closed position.