title: Functional MRI during hyperbaric oxygen: Effects of oxygen on neurovascular coupling and BOLD fMRI signals.
abstract: Hyperbaric oxygen (HBO) therapy is used to treat a number of ailments. Improved understanding of how HBO affects neuronal activity, cerebral blood flow (CBF) and blood-oxygenation-level dependent (BOLD) changes could shed light on the role of oxygen in neurovascular coupling and help guide HBO treatments. The goal of this study was to test two hypotheses: i) activation-induced CBF fMRI response is not dependent on hemoglobin deoxygenation, and ii) activation-induced BOLD fMRI is markedly attenuated under HBO. CBF and BOLD fMRI of forepaw stimulation in anesthetized rats under HBO at 3 atmospheres absolute (ATA) were compared with normobaric air. Robust BOLD and CBF fMRI were detected under HBO. Inflow effects and spin-density changes did not contribute significantly to the BOLD fMRI signal under HBO. Analysis of the T2(⁎)-weighted signal at normobaric air and 1, 2 and 3ATA oxygen in the tissue and the superior sagittal sinus showed a strong dependence on increasing inhaled [O2]. Spontaneous electrophysiological activity and evoked local-field potentials were reduced under HBO. The differences between normobaric air and HBO in basal and evoked electrical activity could not fully account for the strong BOLD responses under HBO. We concluded that activation-induced CBF regulation in the brain does not operate through an oxygen-sensing mechanism and that stimulus-evoked BOLD responses and the venous T2(⁎)-weighted signals still have room to increase under 3ATA HBO. To our knowledge, this is the first fMRI study under HBO, providing insights into the effects of HBO on neural activity, neurovascular coupling, tissue oxygenation, and the BOLD signal.
authors.affiliation: Graduate School of Biomedical Engineering, University of Texas at San Antonio, USA.
authors.forename: Damon P
authors.initials: DP
authors.lastname: Cardenas
authors.affiliation: Department of Ophthalmology, University of Texas Health Science Center, USA; Research Imaging Institute, University of Texas Health Science Center, USA.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Muir
authors.affiliation: Research Imaging Institute, University of Texas Health Science Center, USA.
authors.forename: Shiliang
authors.initials: S
authors.lastname: Huang
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Boley
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Lodge
authors.affiliation: Graduate School of Biomedical Engineering, University of Texas at San Antonio, USA; Department of Ophthalmology, University of Texas Health Science Center, USA; Research Imaging Institute, University of Texas Health Science Center, USA; South Texas Veterans Health Care System, Department of Veterans Affairs, San Antonio, TX, USA. Electronic address: duongt@uthscsa.edu.
authors.forename: Timothy Q
authors.initials: TQ
authors.lastname: Duong
mesh_terms: D000399:Air Pressure; D000818:Animals; D001921:Brain / Q000098:blood supply*; D001931:Brain Mapping; D004558:Electric Stimulation; D006339:Heart Rate; D006439:Hemodynamics; D006454:Hemoglobins / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D008297:Male; D000069336:Neurovascular Coupling; D010100:Oxygen / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D056152:Respiratory Rate; D013003:Somatosensory Cortex / Q000098:blood supply / Q000502:physiology; D055698:Touch Perception / Q000502:physiology
chemical_list: D006454:Hemoglobins; D010100:Oxygen
keywords: BOLD; CBF; Forepaw stimulation; Oxygen therapy