Effect of inhaled oxygen concentration on 129Xe chemical shift of red blood cells in rat lungs

Purpose: To investigate the dependence of dissolved Xe-129 chemical shift on the fraction of inhaled oxygen, FiO(2), in the lungs of healthy rats. Methods: The chemical shifts of Xe-129 dissolved in red blood cells, delta(RBC), and blood plasma and/or tissue, delta(Plasma), were measured using MRS in 12 Sprague Dawley rats mechanically ventilated at FiO(2) values of 0.14, 0.19, and 0.22. Regional effects on the chemical shifts were controlled using a chemical shift saturation recovery sequence with a fixed delay time. MRS was also performed at an FiCO(2) value of 0.085 to investigate the potential effect of the vascular response on dRBC and dPlasma. Results: delta(RBC) increased with decreasing FiO(2) (P =.0002), and delta(Plasma) showed no dependence on FiO(2) (P =.23). delta(RBC) at FiCO(2) = 0 (210.7 ppm +/- 0.1) and at FiCO(2) = 0.085 (210.6 ppm +/- 0.2) were not significantly different (P =.67). delta(Plasma) at FiCO(2) = 0 (196.9 ppm +/- 0.3) and at FiCO(2) = 0.085 (197.0 ppm +/- 0.1) were also not significantly different (P =.81). Conclusion: Rat lung delta(RBC) showed an inverse relationship to FiO(2), opposite to the relationship previously demonstrated for in vitro human blood. Rat lung delta(RBC) did not depend on FiCO(2).

Automated summary

In healthy rats, the dissolved Xe-129 chemical shift in red blood cells showed an increase with decreasing fraction of inhaled oxygen (FiO(2)), while the chemical shift in blood plasma and/or tissue did not depend on FiO(2). Additionally, the dissolved Xe-129 chemical shifts were not significantly different under different levels of inhaled carbon dioxide (FiCO(2)).