FIG. 5.

Microdialysate nuclear magnetic resonance (NMR) measurements of ¹³C labeling: glutamine enrichment. (A) Total glutamine concentration measured using ¹H NMR, in TBI brain, control (non-TBI) brain, and muscle. (B–D) Results from microdialysis perfusion with 3-¹³C lactate (8 mmol/L) for 24 h in brain: TBI or control (non-TBI) “normal”. Although glutamine was detectable in muscle (measured using ¹H NMR), ¹³C fractional enrichment of glutamine above natural abundance was not detectable in resting muscle. Natural abundance of ¹³C was assumed to be 1.1%, and ¹³C fractional enrichment values for glutamine were expressed after subtracting this naturally occurring ¹³C background. For patient identities, see Fig. 4 graph and legend. Data points depict individual measurements, and bars indicate medians and interquartile ranges.