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

Purpose To investigate the dependence of dissolved 129Xe chemical shift on the fraction of inhaled oxygen, FiO2, in the lungs of healthy rats. Methods The chemical shifts of 129Xe dissolved in red blood cells, δRBC, and blood plasma and/or tissue, δPlasma, were measured using MRS in 12 Sprague Dawley rats mechanically ventilated at FiO2 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 FiCO2 value of 0.085 to investigate the potential effect of the vascular response on δRBC and δPlasma. Results δRBC increased with decreasing FiO2 (P = .0002), and δPlasma showed no dependence on FiO2 (P = .23). δRBC at FiCO2 = 0 (210.7 ppm ± 0.1) and at FiCO2 = 0.085 (210.6 ppm ± 0.2) were not significantly different (P = .67). δPlasma at FiCO2 = 0 (196.9 ppm ± 0.3) and at FiCO2 = 0.085 (197.0 ppm ± 0.1) were also not significantly different (P = .81). Conclusion Rat lung δRBC showed an inverse relationship to FiO2, opposite to the relationship previously demonstrated for in vitro human blood. Rat lung δRBC did not depend on FiCO2.