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Relation between cerebrovascular function and hippocampal viscoelastic properties in humans
Author(s) -
Sanjana Faria,
Delgorio Peyton,
DeConne Theodore,
Hobson Joshua,
Johnson Curtis,
Martens Christopher
Publication year - 2021
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2021.35.s1.03801
Subject(s) - viscoelasticity , cardiology , medicine , hyperlipidemia , dyslipidemia , materials science , endocrinology , obesity , composite material , diabetes mellitus
Age‐related memory loss shares many of the same modifiable risk factors as cardiometabolic diseases including cerebrovascular dysfunction and dyslipidemia. Previous studies have reported that declines in memory performance are associated with reduced viscoelastic properties of the hippocampus (HC), a brain structure essential for memory encoding and performance. Acute hypercapnia‐induced increases in cerebral blood flow (cerebrovascular reactivity; CVR) have been shown to temporarily restore brain tissue viscoelasticity; however, nothing is known about the influence of chronically low CVR on HC viscoelastic properties. Therefore, the primary aim of this study was to examine the independent association between CVR and HC viscoelastic properties in cognitively normal young and middle‐aged adults. We hypothesized that low CVR would be associated with reduced HC viscoelasticity. As a secondary aim, we also explored the influence of serum triglycerides (TGs) on CVR as our own previous work has demonstrated an association between TGs and HC viscoelasticity. We enrolled 22 generally healthy adults, who were not taking a statin or other lipid‐lowering medication (9 F/13 M, mean age: 41±15 y; age range: 22‐69 y; mean BMI: 27±5 kg/m 2 ; mean BP: 113±11/71±10 mmHg; mean HR: 62±9 bpm). HC viscoelastic properties were measured using magnetic resonance elastography (MRE). MRE data were acquired using a Siemens 3T Magnetom Prisma MRI scanner to image shear waves generated via a pneumatic actuator (Resoundant, Rochester, MN) at 50Hz. Bilateral HC damping ratio (ξ) was calculated from a complex shear modulus derived from a nonlinear inversion algorithm. Higher ξ values indicate reduced elasticity of neural tissue and hence, poorer HC integrity. CVR of the middle cerebral artery (MCA) to acute hypercapnia (+9mmHg P ET CO 2 ) was acquired using Transcranial Doppler and RespirAct TM , a prospective end‐tidal targeting system. Blood TG levels were assessed from a 12‐hour fasted blood draw. Independent associations among CVR, HC viscoelasticity and TGs were performed using simple linear regressions. HC ξ was negatively associated with CVR (r=‐0.42, P=0.0497). CVR was inversely associated with serum TGs (r=‐0.45, P=0.0343). These findings suggest that chronically low CVR is associated with poorer HC integrity. Elevated concentration of TGs in the blood may potentially explain the relation between CVR and HC viscoelasticity.