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

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Abstract
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˙i) and expired ventilation (V˙e). The devices were connected to two systems sampling expired O2and CO2from a single mixing chamber. Simultaneously, the criterion (Douglas bag, or DB) method assessed V˙e and fractions of O2and CO2in expired gas (FeO2and FeCO2) for subsequent calculation of O2uptake (V˙o2), CO2production (V˙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), andV˙o2(inspired system only), the differences were extremely small (FeO2= 0.0004, FeCO2= −0.0003,V˙o2= −0.018 l/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.