In 5 cases of mitral disorders and 8 cases of miscellaneous diseases (13 cases in all), gas characteristics and acid-base balance of so-called PC (pulmonary capillary) blood were observed in comparison with those of mixed arterial, mixed venous and capacity blood, and the following results were obtained:
1) Compared with mixed arterial and mixed venous blood, O
2 content, O
2 saturation and O
2 partial pressure showed the highest values in PC blood, while CO
2 content, plasma HCO
3-, H2CO
3 and CO
2 partial pressure were the lowest in PC blood.
2) The reason why the CO
2 content of PC blood is remarkably low and close to that of capacity blood is not because PC blood has passed through alveoli twice but because shunting blood which has never passed alveoli streams into PC blood only in a small amount. As CO
2 partial pressure of PC blood is considered to be very close to that of alveolar air CO
2 partial pressure of PC blood instead of that of mixed arterial blood which has been hitherto used should be employed as CO
2 partial pressure of alveolar air for various kinds of calculations,
3) What makes O
2 partial pressure of PC blood higher than that of mixed arterial and mixed venous blood is the fact that the former contains large amount of blood which has passed through alveoli more frequently.
4) Mean blood pressure and O
2 partial pressure of PC blood show a fairly good correlation (r=-0.68, 0.02>p>0.01).
5) While plasma HCO
3 of PC blood is lower than that of mixed arterial and mixed venous blood, anionized hemoglobin and anionized plasma protein are higher in PC blood than in mixed arterial and venous blood. Therefore, total buffer base of PC blood has no remarkable difference from the other samples. However, since CO
2 partial pressure of PC blood is the lowest, pH in PC blood tends to alkaline.
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