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

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 O2 and CO2 from a single mixing chamber. Simultaneously, the criterion (Douglas bag, or DB) method assessed V˙e and fractions of O2and CO2 in expired gas (Fe O2 and Fe CO2 ) for subsequent calculation of O2 uptake (V˙o 2), CO2 production (V˙co 2), 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 Fe O2 (both inspired and expired systems), Fe CO2 (expired system only), andV˙o 2 (inspired system only), the differences were extremely small (Fe O2 = 0.0004, Fe CO2 = −0.0003,V˙o 2 = −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.