GAS MIXING APPARATUS FOR DETERMINING CARDIAC-OUTPUT BY CO2 REBREATHING

The carbon dioxide rebreathing technique is widely used for determinat ion of cardiac output during exercise. The equilibration method of Col lier et al. (J. Appl. Physiol. 9:25, 1956) is generally preferred over the exponential method of Defares (J. Appl. Physiol. 13:159, 1968). H owever, the equilibration method requires the volume and initial CO2 p ercentage in the rebreathing bag to be adjusted according to the work rate. A device for mixing two gases (100% O-2 and 20% CO2/80% O-2) was constructed for this purpose. Multistage regulators are attached to t he gas tanks and connected to a medical gas mixer via high-pressure ai r hoses. A variable time-delay switch causes a solenoid Valve to open for 1.0-10 s to deliver a predetermined gas volume. The device was fou nd to accurately deliver a preset volume and concentration of gas to t he rebreathing bag. A gas mixing apparatus simplifies the equilibratio n CO2 rebreathing technique by allowing the investigator to easily sel ect the initial volume and percentage of CO2.