Acute Lower Body Negative Pressure Changes Human Brain Tissue Perfusion and Stiffness in vivo Measured with MR Elastography

• Gabriella Dunay, Biomedical Engineering, University of Delaware

• Curtis Johnson, Biomedical Engineering, University of Delaware

Understanding the relationship between brain tissue integrity and cardiovascular health offers many opportunities to improve health care interventions for aging patients. Brain tissue stiffness, measured with magnetic resonance elastography (MRE), can be used as a sensitive metric of brain health that decreases with increasing age and even further with neurodegenerative disease progression. Previous associations between brain stiffness and blood flow have been examined, but the relationships are not fully understood. The objective of this study is to establish that applied LBNP induces a measurable change in brain stiffness and cerebral blood flow and to examine the association between both. To do this, we use lower body negative pressure (LBNP) to observe the acute effects of decreased blood flow on brain stiffness in healthy young adults. LBNP is a method wherein negative pressure is applied below the iliac crest (hips) to reduce central venous pressure and venous return, thus more of the subject’s blood remains in their lower body, which consequently decreases the blood flow in their brain. The decrease in brain blood flow may affect brain stiffness due to decreased intracranial pressure or changing mechanical properties of the arteries and perivascular tissue. We use MRE while applying LBNP to measure brain stiffness changes, and also use arterial spin labeling (ASL), a non-invasive MRI technique measuring tissue perfusion that doesn’t require any type of injected contrast. After imaging sixteen subjects using a Siemens 3T Prisma MRI scanner and a LBNP chamber to collect ASL and MRE images and data, we found that overall, there is a directly proportional relationship between the observable change in stiffness and perfusion and a temporary change in both can be accomplished using LBNP. This ultimately provides an avenue to understand the intricate relationships between brain integrity and vascular health.