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

Om hvordan CO2 endrer seg under trening og at CO2 handler mest om å regulere pH.

«Although the mean mixed venous PCO 2 rose from 47 Torr at rest to 59 Torr at the lactic acidosis threshold (LAT) and further to 78 Torr at Max, the Cv̄CO2 rose from 22.8 mM at rest to 25.5 mM at LAT but then fell to 23.9 mM at Max.»

«We conclude that changes in buffer base and pH dominate the PCO 2-CCO 2 relationship during exercise, with changes in Hb and blood oxyhemoglobin saturation exerting much less influence.»

«This study discloses several important findings. 

1) During exercise, CCO 2 and [HCO Formula ] do not consistently increase in proportion to PCO 2

2) Because of the acidemia caused by increased lactate production, Cv̄CO2 and mixed venous [HCO Formula ] decrease to near resting values as maximalV˙O 2 is approached, despite increasing Pv̄CO2

3) Above LAT, while Pv̄CO2 increases to high levels, PaCO2 decreases because of ventilatory compensation for the exercise lactic acidosis; consequently, CaCO2 decreases to a greater degree than does Cv̄CO2

4) The increase in Cv̄CO2-CaCO2during exercise is mainly due to the increase in Cv̄CO2 below LAT and the decrease in CaCO2 above LAT.

5) Changes in SO 2 and Hb have minor influences on the PCO 2-CCO 2 relationship during exercise, whereas changes in pH due to changes in buffer base have a major influence.

6) Because pHdecreases more than pHa, there are large errors in calculated Cv̄CO2-CaCO2 when the pH change is ignored. 

7) At rest and during all levels of exercise, over threefourths of the total CO2exchange from the blood to lung gas (i.e., Cv̄CO2-CaCO2) is due to dissociation of [HCO Formula ], whereas less than one-fourth is due to the combination of venoarterial differences in [CO2] and [NH-CO2] at rest to Max.»

«It is clear that the dissociation of [HCO Formula ] plays the dominant role in CO2 exchange at the lung, whereas [CO2] and [NH-CO2] play smaller roles in total CO2 exchange. Although PCO 2differences account for the transfer of CO2 out of blood, >75% of the quantity transferred comes from the dissociation of mixed venous [HCO Formula ].»

«We have shown that Cv̄CO2 in blood actually decreases during exercise above the LAT, despite increasing PCO 2. The major reason for this is that the CO2 dissociation curve is shifted downward when lactic acid is generated during exercise.»

Her er CO2 Disossiation Curve: 

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