The Response of Extracellular Hydrogen Ion Concentration to Graded Degrees of Chronic Hypercapnia: The Physiologic Limits of the Defense of pH*

It is now well recognized that the defense of extracellular pH during acute hypercapnia de- pends upon generation of bicarbonate by body buffers (1). Recently, the quantitative charac- teristics of this defense have been defined in acute studies of the acid-base response of the intact organism to stepwise increases in carbon dioxide tension (2, 3). Similar observations are not available, however, for chronic hypercapnia in which defense of pH is enhanced by renal gen- eration of bicarbonate.