Effect of chronic hypoxic hypoxia on the O 2-Hb dissociation curve and respiratory gas transport in man

Abstract

The effect of chronic hypoxic hypoxia on the O 2-Hb dissociation curve and O 2 and CO 2 transport was determined in three groups of subjects: residents at altitude, patients with enital heart disease and patients with chronic obstructive lung disease. A shift to the right of the O 2-Hb dissociation curve of normal, non hypoxic subjects, was found in all subjects of the first 2 groups (P50 = 30.6 mm Hg at pH = 7.4). The magnitude of the shift was not related to the hemoglobin concentration. In residents at altitude it was independent of the duration of the stay. In patients with chronic lung disease the direction of the shift depended upon the hematocrit, being leftward when Hct is normal (P50 = 24.7 mm Hg) and rightward in polycythemic patients (Hct 50%; P50 = 29.2 mm Hg). Our data reveal differences in CO 2 transport between the 3 groups of subjects that corroborate previously reported findings. The causes and mechanisms of the shift are discussed. Low oxygen saturation in the venous blood appears to be the regulating factor, and changes occurring in the concentration of some intracellular constituents seem to be the mechanism of action. The physiological effects of the shift (left and right) are discussed.