Carbon dioxide pressure-concentration relationship in arterial and mixed venous blood during exercise

dioxide pressure-concentration relationship in arterial and mixed venous blood during exercise. J Appl Physiol 90: 1798–1810, 2001.—To calculate cardiac output by the indi-rect Fick principle, CO2 concentrations (CCO2) of mixed ve-nous (Cv#CO2) and arterial blood are commonly estimated from PCO2, based on the assumption that the CO2 pressure-con-centration relationship (PCO2-CCO2) is influenced more by changes in Hb concentration and blood oxyhemoglobin satu-ration than by changes in pH. The purpose of the study was to measure and assess the relative importance of these vari-ables, both in arterial and mixed venous blood, during rest and increasing levels of exercise to maximum (Max) in five healthy men. Although the mean mixed venous PCO2 rose from 47 Torr at rest to 59 Torr at the lactic acidosis threshold (LAT) and further to 78 Torr at Max, the Cv#CO2 rose from 22.