Abstract: A calibration syringe for controllably delivering gas to a respiratory gas measuring instrument during the calibration thereof. In addition to the piston and cylinder arrangement used in prior syringes, the calibration syringe of the invention includes several improvements which enhance the accuracy and repeatability of the volume of gas delivered thereby. One improvement comprises a modified inlet-outlet design which assures a positive shutoff of the flow of gas at the end of an ejection stroke. A second improvement comprises the provision of a spring-loaded mechanism for automatically propelling the piston at any of several operator selectable rates. Finally, the calibration syringe of the invention includes a latching arrangement which assures that each ejection stroke begins from the same starting position and is initiated in a way that minimizes operator-related effects.

Abstract: An improved switching device for indicating the beginning and ending of the breath of a test subject. A flow through housing is provided with an inlet and first and second outlets. A flexible diaphragm is connected in series with the first outlet to serve as a check valve which opens during the high flow rate portion of a breath. A sensitive flow responsive member connected in series with the second outlet opens in response to the presence of gas flow during the low flow rate portion of the breath. A detecting circuit responsive to the position of the flow responsive member accurately signals the beginning and ending of a breath. A damping member connected to the flexible diaphragm prevents the latter from vibrating at low breath flow rates and thereby stabilizes the motion of the flow responsive member.

Abstract: An improved gas volume calibration method and apparatus for use in respiratory gas analyzers. A control unit monitors the flow of calibration gas through the analyzer by monitoring the electrical signals produced by a gas turbine and a breath switch. During calibration, a known volume of calibration gas is repeatedly delivered to the analyzer from a calibration syringe at each of a number of different flow rates. On the basis of the information received from the turbine and the breath switch, the control unit generates and stores a piecewise linear approximation of the nonlinear characteristic of the turbine. This stored turbine characteristic is then made available during subsequent measurements to eliminate those volume errors which are associated with variations in the rate at which the sample gas is delivered, thereby affording measurements of improved accuracy.

Abstract: A gas dryer cartridge for removing the moisture from a sample gas stream prior to the application thereof to a metabolic measuring instrument. A dryer housing having an inlet and an outlet is partitioned into a first, gas drying chamber containing a desiccant and a second, liquid collecting chamber containing an absorbent liquid retaining element. The volume of the liquid collecting chamber is made sufficiently large that it can contain the liquid produced in the event that the desiccant is liquefied as a result of prolonged use. The liquid retaining element prevents the collected liquid from being swept up in the gas stream during the removal or replacement of the cartridge.