Validity of inspiratory and expiratory methods of measuring gas exchange with a computerized system

The accuracy of a computerized metabolic system, using inspiratory and expiratory methods of measuring ventilation, was assessed in eight male subjects. Gas exchange was measured at rest and during five stages on a cycle ergometer. Pneumotachometers were placed on the inspired and expired side to measure inspired ((V) over dot I) and expired ventilation ((V) over dot E). The devices were connected to two systems sampling expired O-2 and CO2 from a single mixing chamber. Simultaneously, the criterion (Douglas bag, or DB) method assessed (V) over dot E and fractions of O-2 and CO2 in expired gas (FEO2 and FECO2) for subsequent calculation of O-2 uptake ((V) over dot O-2), CO2 production ((V) over dot CO2), and respiratory exchange ratio. Both systems accurately measured metabolic variables over a wide range of intensities. Though differences were found between the DB and computerized systems for FEO2 (both inspired and expired systems), FECO2 (expired system only), and (V) over dot O-2 (inspired system only), the differences were extremely small (FEO2 = 0.0004, FECO2 = -0.0003, (V) over dot O-2 = -0.018 1/min). Thus a computerized system, using inspiratory or expiratory configurations, permits extremely precise measurements to be made in a less time-consuming manner than the DB technique.