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

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