Freedivers can endure severe hypoxemia during breathhold without any apparent neurological deficit. Little is known on how brain circulation adapts to deliberate breathhold. We examined 14 experienced freedivers during breathholds of 5 to 7.5 minutes at a 3T MRI applying 3D-pCASL and IVIM-MRI sequences to reveal dynamic alterations of cerebral blood flow (rCBF) and in order to elucidate the relationship of rCBF and perfusion fraction (PF) of IVIM-MRI. rCBF increased to 3.2-fold the baseline levels and negatively correlated to blood oxygen levels, but not to PF, which initially dropped during breathhold and therefore appears to represent another underlying physiological mechanism.
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