Impact of Head‐Down Position on Cerebral Blood Flow in Healthy Subjects: An Arterial Spin‐Labeling MR Perfusion Study

BACKGROUND: A head-down (HD) position is used in some stroke centers to maintain cerebral perfusion (CP) in stroke patients. PURPOSE: To assess CP in healthy volunteers in the supine and HD (-15 degrees ) positions. STUDY TYPE: Prospective. POPULATION: Eighteen healthy subjects of 53 (+/-8) years old. FIELD STRENGTH/SEQUENCE: 1.5T / arterial spin-labeling (ASL) in the supine position and after 4 minutes of HD position. ASSESSMENT: Regions of interest from reconstructed cerebral blood-flow (CBF) maps: subcortical nuclear gray matter (accumbens, amygdala, caudate, hippocampus, pallidum, putamen, thalamus), cortical gray matter (cGM), and white matter (WM). We also monitored hemodynamic parameters. STATISTICAL TESTS: Shapiro-Wilk test, analysis of variance (ANOVA) tests, Student's t-tests, and Pearson correlation analysis. RESULTS: CBF was higher in women compared to men, whatever the position (mean difference of 17% in supine, and 13% in HD position). From supine to HD position, CBF was decreased in all regions (mean decrease of -7%). Simultaneously, mean arterial pressure and systolic blood pressure increased (respectively P = 0.004 and P < 0.001). DATA CONCLUSION: The CBF decrease, despite increased hemodynamic parameters, may indicate efficient cerebral autoregulation. Our results seem to reflect only early cerebral autoregulation stages but may open the way towards a more precise understanding of CP. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:218-224.