The Interaction of Carbon Dioxide with the Rate of Exchange of Oxygen by Red Blood Cells

Abstract

An objective of ‘in vitro’ studies of the rate of exchange of oxygen by haemoglobin in the red blood cell is to be able to precisely state the rates of these processes occurring ‘in vivo’ and at the same time provide a quantitative understanding of the biophysical and physicochemical mechanisms involved. It has not yet proven possible ‘in vitro’ to simulate the ‘in vivo’ conditions, involving as they do rapid changes of haemoglobin saturation with oxygen, pH, carbon dioxide interactions, C1⁻/HCO₃ ⁻ movement, osmotic pressure and many other factors. In order to start to understand this process, the rate of oxygen exchange has mainly been studied in dilute suspensions, maintaining other factors constant, and observing the complete change from zero to l00% saturation of oxyhaemoglobin. A theoretical analysis of this situation, based on a process of diffusion through the cell membrane, followed by diffusion through and chemical reaction with the internal haemoglobin, was first given by Roughton (1). Even then, certain simplifications, such as the representation of a biconcave erythrocyte as equivalent to a thin layer of haemoglobin covered by a membrane, were necessary in order to obtain an analytical solution. More recently, in a full review, Roughton (2) has provided convincing evidence that these simplifications are acceptable and that for the majority of ‘in vitro’ observations on the rate of uptake of gaseous ligands by erythrocytes, equilibrated with an oxygen-free gas phase, the theoretical analysis is valid.