The effect of high altitude adaptation on brain oxygenation
Dunn, J.F., O. Grinberg, M. Roche, C. Nwaigwe, H. Hou and H.M. Swartz
NMR and EPR Research Centers, Dept. of Diagnostic Radiology, Hanover NH.
03755
INTRODUCTION: The mammalian brain has an absolute requirement for
oxygen and yet the associated control mechanisms
result in variations in pO2 in different regions of brain (1). It has been
recently determined that the brain is
capable of changing capillary densities, and therefore oxygen delivery, in
response to chronic exposure to
low oxygen (2,3). Electron paramagnetic resonance oximetry can be used to
monitor brain oxygenation in
situ. We used EPR oximetry to monitor the pO2 in rat brain (under normo-baric
conditions) cortex during a
time-course of adaptation to low oxygen induced through exposure to
hypo-baric conditions.
METHODS: Rats were placed in drums which had vacuum lines attached to
reduce the internal pressure to 380mmHg.
Interstitial pO2 measurements were all made under normo-baric conditions in
awake animals. Controls were
housed at normo-baric pressure. LiPc (lithium phthalocyanine) crystals (4)
implanted under anesthesia
(Isoflurane 2.5%, FiO2 30%) into the frontal cortex 1 week before the study.
EPR oximetry was done on
awake, restrained animals using an L-band spectrometer.
RESULTS AND DISCUSSION: Brain oxygenation, measured under normo-baric
conditions (normal pO2), increased rapidly in the first 7
days, then stabilized. There is no reason to believe that brain metabolic
rate for oxygen has changed
markedly during this acclimation. This indicates that an increase in
capillary density, as observed to occur
during this acclimation protocol, results in an increased brain oxygenation.
The use of EPR oximetry was
considered key to the success of this project since it allowed us to monitor
brain oxygenation in individual animals over many weeks.
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