Dr. Bassett et Tr. Fitton, GAS MIXING APPARATUS FOR DETERMINING CARDIAC-OUTPUT BY CO2 REBREATHING, Medicine and science in sports and exercise, 27(12), 1995, pp. 1698-1702
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.