Daniel A. Handwerker1, Paula Wu1,2, Ronald M. Harper3, Peter A. Bandettini1,4
1Section on Functional Imaging Methods, National Institute of Mental Health, Bethesda, MD, United States; 2Neuroscience, University of California, Los Angeles, Los Angeles, CA, United States; 3Neurobiology, David Geffen School of Medicine, UCLA, Los Angeles, CA, United States; 4Functional MRI Facility, National Institute of Mental Health, Bethesda, MD, United States
Hypercapnia creates global changes in cerebral blood flow, volume, and oxygenation that can be measured with fMRI and used for calibration. Breath-holding is a simple way to induce hypercapnia, but it may alter thoracic chest pressure and include a ValSalva effect. We alter chest pressure while keeping the hold duration constant to see how the BOLD signal changes. The initial BOLD undershoot and following peak scale with pressure. Because the precise contrast mechanisms behind these changes are not fully understood, they may be a confound in calibration studies, or a novel way to rapidly induce calibration-useful global BOLD signal changes.