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.