Blood gases at several levels of oxygenation in rats with a left-shifted blood oxygen dissociation curve

Abstract

Theoretical deductions have shown that a shift of the blood O₂ dissociation curve (ODC) to the right might improve O₂ transport to tissues at normoxia and at mild hypoxia whereas at severe hypoxia the organism should be better off with an ODC shifted to the left (Turek et al., 1973b; Turek and Kreuzer, 1976). The present study was performed in order to ascertain this ambiguous effect of an ODC shift depending on the degree of hypoxia in intact animals. A major displacement of the ODC to the left was achieved in rats by chronic administration of sodium cyanate (NaOCN). Control animals received sodium chloride (NaCl) instead. Arterial and mixed-venous$P_{{\text{O}}_{\text{2}} }$,$P_{{\text{CO}}_{\text{2}} }$, and pH were measured at normoxia and during breathing 14.9, 8.0, or 5.6% O₂ in N₂ in both groups. From$P_{{\text{O}}_{\text{2}} }$, pH, ODC and arterial hematocrit, arterial and mixed-venous O₂ contents were estimated and$({\text{a}} - {\text{v)}}_{{\text{O}}_{\text{2}} }$ as an index of blood O₂ extraction was obtained. At normoxia and during breathing 14.9% O₂ the NaOCN rats had a lower mixed-venous$P_{{\text{O}}_{\text{2}} }$ than the NaCl rats without any difference in pH. Arterio-venous O₂ difference did not differ at normoxia but was lower in NaOCN rats at 14.9% O₂. However, at 8.0 and 5.6% O₂ the NaOCN rats had a higher mixed-venous$P_{{\text{O}}_{\text{2}} }$, an increased$({\text{a}} - {\text{v)}}_{{\text{O}}_{\text{2}} }$, and a higher pH (arterial and mixed-venous). At 5.6% O₂ the NaCl rats developed a severe acidosis concomitant with pronounced hypocapnia. These findings confirm that rats with a left-shifted ODC have an impaired O₂ transport to tissues at normoxia and mild hypoxia but a more efficient O₂ transport at severe hypoxia as compared with rats with an unshifted ODC, in agreement with our previous theoretical studies.