Time-Course of Ventilation, Arterial and Pulmonary CO2 Tension During CO2 Increase in Humans

A change of ventilation (VE), PaCO2 (arterial CO2 tension) and PvCO(2) (pulmonary arterial CO2 tension) with time was not evaluated precisely during exercise or CO2 rebreathing in humans. In this study, changes of these variables with time were fitted to exponential curves {y=Exp (x/ T + A) + k} and compared. When exercise pulmonary hemodynamics was examined in 15 cardiac patients to decide therapies, we asked the patients to undergo CO2 rebreathing using air with supplementation of consumed O-2. Arterial and pulmonary blood was drawn every minute. During exercise, T was 28.2 +/- 8.4 and 26.8 +/- 12.4, and A was 0.80 +/- 0.50 and 0.50 +/- 0.90 in VE and PvCO(2), respectively, with no statistical differences. During CO2 rebreathing, T was 18.6 +/- 5.8, 41.8 +/- 38.0 and 21.6 +/- 9.7 and A was 0.39 +/- 0.67, 1.64 +/- 1.35 and 0.17 +/- 0.83 in VE, PaCO2 and PvCO(2), respectively, with statistical difference of PaCO2 from other variables, suggesting that VE and PvCO(2) showed same mode of change according to time but PaCO2 did not.