Francis C M, Foëx P, Ryder W A
Respir Physiol. 1980 May;40(2):149-64. doi: 10.1016/0034-5687(80)90089-4.
Two types of titration curve (log PCO2 vs. pH and whole blood [HCO3-] vs. pH) were obtained in anaesthetized dogs by altering FICO2. Both plots reveal a significant progressive decrease in slope from arterial(a) to mixed venous (v) to coronary sinus (cs) blood. Lines drawn between corresponding points on the arterial and mixed venous or coronary sinus curves have slopes determined by the Respiratory Exchange Ratio (R) and are called R lines. Differences in slope between arterial and venous (v or cs) curves may be due to changes in blood flow or of delivery of CO2 to the blood. The former is indicated by constant R values at different CO2 tensions whilst the latter is a reflection of changing R values due to fluctuations in CO2 stores. The myocardium is not an important store for CO2 but CO2 has a profound effect on coronary blood flow and it is this that causes the difference in a-cs slopes. The reverse is true for skeletal muscle where the charging and discharging of CO2 stores brings about the difference in a-v slopes.
通过改变动脉血二氧化碳分压（FICO2），在麻醉犬身上获得了两种滴定曲线（log PCO2对pH以及全血[HCO3-]对pH）。两条曲线均显示，从动脉血（a）到混合静脉血（v）再到冠状窦血（cs），斜率显著逐渐降低。在动脉血与混合静脉血或冠状窦血曲线的对应点之间绘制的线，其斜率由呼吸交换率（R）决定，这些线被称为R线。动脉血与静脉血（v或cs）曲线之间斜率的差异可能是由于血流变化或二氧化碳向血液输送的变化所致。前者由不同二氧化碳张力下恒定的R值表示，而后者反映了由于二氧化碳储备波动导致的R值变化。心肌不是二氧化碳的重要储备部位，但二氧化碳对冠状动脉血流有深远影响，正是这一点导致了动脉血与冠状窦血曲线斜率的差异。对于骨骼肌而言，情况则相反，二氧化碳储备的增减导致了动脉血与静脉血曲线斜率的差异。
