Effect of inhaled oxygen concentration on Xe-129 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).