title: Whole-Brain N-Acetylaspartate Concentration Is Preserved during Mild Hypercapnia Challenge.
abstract: OBJECTIVE
  Although NAA is often used as a marker of neuronal health and integrity in neurologic disorders, its normal response to physiologic challenge is not well-established and its changes are almost always attributed exclusively to brain pathology. The purpose of this study was to test the hypothesis that the neuronal cell marker NAA, often used to assess neuronal health and integrity in neurologic disorders, is not confounded by (possibly transient) physiologic changes. Therefore, its decline, when observed by using (1)H-MR spectroscopy, can almost always be attributed exclusively to brain pathology.
  
  
  METHODS
  Twelve healthy young male adults underwent a transient hypercapnia challenge (breathing 5% CO2 air mixture), a potent vasodilator known to cause a substantial increase in CBF and venous oxygenation. We evaluated their whole-brain NAA by using nonlocalizing proton MR spectroscopy, venous oxygenation with T2-relaxation under spin-tagging MR imaging, CBF with pseudocontinuous arterial spin-labeling, and the cerebral metabolic rate of oxygen, during normocapnia (breathing room air) and hypercapnia.
  
  
  RESULTS
  There was insignificant whole-brain NAA change (P = .88) from normocapnia to hypercapnia and back to normocapnia in this cohort, as opposed to highly significant increases: 28.0 ± 10.3% in venous oxygenation and 49.7 ± 16.6% in global CBF (P < 10(-4)); and a 6.4 ± 10.9% decrease in the global cerebral metabolic rate of oxygen (P = .04).
  
  
  CONCLUSIONS
  Stable whole-brain NAA during normocapnia and hypercapnia, despite significant global CBF and cerebral metabolic rate of oxygen changes, supports the hypothesis that global NAA changes are insensitive to transient physiology. Therefore, when observed, they most likely reflect underlying pathology resulting from neuronal cell integrity/viability changes, instead of a response to physiologic changes.
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York.
authors: S
authors: S
authors: Chawla
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York yulin.ge@nyumc.org oded.gonen@nyumc.org.
authors: Y
authors: Y
authors: Ge
authors: The Russell H. Morgan Department of Radiology and Radiological Science (H.L.), Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors: H
authors: H
authors: Lu
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York.
authors: O
authors: O
authors: Marshall
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York.
authors: M S
authors: MS
authors: Davitz
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York.
authors: G
authors: G
authors: Fatterpekar
authors: Department of Radiology (B.J.S.), Center for Advanced MR Development, Duke University Medical Center, Durham, North Carolina.
authors: B J
authors: BJ
authors: Soher
authors: From the Department of Radiology (S.C., Y.G., O.M., M.S.D., G.F., O.G.), Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York yulin.ge@nyumc.org oded.gonen@nyumc.org.
authors: O
authors: O
authors: Gonen
mesh_terms: D000328:Adult; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry / Q000502:physiology*; D006801:Humans; D006935:Hypercapnia / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D055815:Young Adult
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate