Effects of oxygen and carbon dioxide on mean cell volume

Changes in mean cell volume (MCV) following addition of CO2, O2 or both to venous blood treated with ethylenediaminetetraacetic acid were studied in an attempt to evaluate the effects of saturation with these gases. The MCV before the addition was taken to be 100%. When CO2 was mixed with each of 353 samples, the mean increase (+/- SD) was 6.10 +/- 1.72%. When O2 was added to 335 specimens, the mean decrease was 1.42 +/- 0.96%. When first CO2 and then O2 was added to 266 samples, the mean change (the sum for each sample of the absolute value of the increase plus that of the decrease) was 7.39 +/- 1.90%. Results of samples of venous and arterial blood from 15 subjects were compared to check these observations in vivo. The MCV of venous blood was always larger than that of arterial blood.