Contribution of Red Cell-Plasma H⁺ Disequilibrium to Alveolar-Blood ${{\text{P}}_{C{O_2}}}$ Differences During Rebreathing

Abstract

In recent years, a number of investigators have observed that arterial and/or mixed venous ${{\text{P}}_{C{O_2}}}$ can be lower than alveolar ${{\text{P}}_{C{O_2}}}$ during conditions when no CO₂ is exchanged in the lung capillaries. The range of values reported for these differences has been exceptionally wide. For example, in one laboratory, careful studies with several different preparations failed to reveal any ${{\text{P}}_{C{O_2}}}$ differences between alveolar gas and blood [7]. Other laboratories have reported that the ${{\text{P}}_{C{O_2}}}$ differences can become quite large during exercise [6] or acidosis [5]. The wide range of reported values probably reflects the many technical difficulties involved in obtaining such data. Several explanations have been proposed for these differences, but none has been entirely accepted to date.