Device for Automatic Measurement of Oxygen Consumption in Closed Circuit Type of Metabolism Apparatus

Abstract

In the closed circuit type of metabolism apparatus the measurement of oxygen consumption is usually dependent upon changes in the internal pressure of the system. Inasmuch as carbon dioxide is rapidly removed by absorption in alkali, the consumption of oxygen necessarily leads to a reduction in pressure in a system of given volume. The rate of oxygen consumption is then ordinarily determined by measurement of the quantity of oxygen that must be added for restoration of the original pressure, or by compression of the residual gas through the addition of a measured volume of liquid. 1 , 2

The device now to be described is based upon the latter principle, and permits automatic measurement of the volume of liquid that must be added to maintain a constant pressure within the system. It consists of a 4-liter bottle which serves as an oxygen reservoir, connected above with the measuring unit proper. This is a 15 cc. cylindrical cup into which water flows from an external feed line as the pressure decreases in the metabolism apparatus. As the cup fills, a float, carrying a light platinum bridge, rises and breaks an electrical contact which is maintained through mercury tubes in the base of the cup. This interruption in the circuit is recorded by a magnetically operated needle on a smoked-paper kymograph. At the same time the cup empties through a syphon attached to the side, the electrical contact is remade, and the water discharged from the cup passes through the syphon outlet into the oxygen reservoir. The displaced oxygen rises through a second tube and enters the space in the upper part of the cup. From here 2 other tubes run. The first, a mere capillary, is connected as a side line with the main circuit of the metabolism apparatus through which air is circulated by a blower.