Temporal dynamics of lactate concentration in the human brain during acute inspiratory hypoxia

Purpose: To demonstrate the feasibility of measuring the temporal dynamics of cerebral lactate concentration and examine these dynamics in human subjects using magnetic resonance spectroscopy (MRS) during hypoxia. Materials and Methods: A respiratory protocol consisting of 10-minute baseline normoxia, 20-minute inspiratory hypoxia, and ending with 10-minute normoxic recovery was used, throughout which lactate-edited MRS was performed. This was repeated four times in three subjects. A separate session was performed to measure blood lactate. Impulse response functions using end-tidal oxygen and blood lactate as system inputs and cerebral lactate as the system output were examined to describe the dynamics of the cerebral lactate response to a hypoxic challenge. Results: The average lactate increase was 20% +/- 15% during the last half of the hypoxic challenge. Significant changes in cerebral lactate concentration were observed after 400 seconds. The average relative increase in blood lactate was 188% +/- 95%. The temporal dynamics of cerebral lactate concentration was reproducibly demonstrated with 200-second time bins of MRS data (coefficient of variation 0.063 +/- 0.035 between time bins in normoxia). The across-subject coefficient of variation was 0.333. Conclusion: The methods for measuring the dynamics of the cerebral lactate response developed here would be useful to further investigate the brain's response to hypoxia. J. Magn. Reson. Imaging 2013;37:739745. (c) 2012 Wiley Periodicals, Inc.