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Measurement of mixed venous carbon dioxide pressure by rebreathing during exercise. 1985

G Alves da Silva, and A el-Manshawi, and G J Heigenhauser, and N L Jones

This study compared rebreathing methods currently used for the measurement of mixed venous PCO2 (PVCO2) during exercise. Four mathematical procedures were used to derive the asymptote of the exponential rise in end-tidal PCO2 during 15 sec rebreathing of low (2-6%) CO2 mixtures ('exponential' methods); the derived PVCO2 was compared to that obtained with an 'equilibrium' method, in which high CO2 mixtures were rebreathed to obtain an equilibrium of CO2 between the lungs and rebreathing bag. Precision was established by analysing duplicate rebreathings at each power output. The most precise of the four exponential procedures (coefficient of determination 0.98) used iterative statistical analysis to obtain an equation for the best fit curve of end-tidal PCO2 with time (t), solved for t = 20 sec. The PVCO2 derived by this procedure was similar to that obtained by the equilibrium method (r = 0.96), and both yielded estimates of cardiac output that were within the previously published expected range. Variations in the initial rebreathing bag volume and CO2 concentration, and in the breathing frequency during rebreathing had little effect on the derived PVCO2.

UI MeSH Term Description Entries
D008297 Male Males
D010313 Partial Pressure The pressure that would be exerted by one component of a mixture of gases if it were present alone in a container. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed) Partial Pressures,Pressure, Partial,Pressures, Partial
D010827 Physiology The biological science concerned with the life-supporting properties, functions, and processes of living organisms or their parts.
D012119 Respiration The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration ( Breathing
D002245 Carbon Dioxide A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals. Carbonic Anhydride,Anhydride, Carbonic,Dioxide, Carbon
D002302 Cardiac Output The volume of BLOOD passing through the HEART per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with STROKE VOLUME (volume per beat). Cardiac Outputs,Output, Cardiac,Outputs, Cardiac
D005082 Physical Exertion Expenditure of energy during PHYSICAL ACTIVITY. Intensity of exertion may be measured by rate of OXYGEN CONSUMPTION; HEAT produced, or HEART RATE. Perceived exertion, a psychological measure of exertion, is included. Physical Effort,Effort, Physical,Efforts, Physical,Exertion, Physical,Exertions, Physical,Physical Efforts,Physical Exertions
D005260 Female Females
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000328 Adult A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available. Adults

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