Relationship between cardiac index and brain volume in the UK Biobank.

Aims: Although cardiac function is associated with cognitive impairment in end-stage heart disease, the links between cardiac function and brain structure remain unclear. We aimed to examine the association between cardiac index (CI) (a measure of cardiac output adjusting for body surface area) and brain volumes in mid-to later life and how these are affected by age, sex and cardiometabolic factors. Materials and methods: We utilized brain and cardiac magnetic resonance imaging (MRI) data from a population-based cohort of people in the UK Biobank (a United Kingdom population-based cohort of people > 40 years old) at mid to later life. Linear regression modelling was used to examine associations of CI with total brain volume (TBV), gray matter (GMV), white matter (WMV), white matter hyperintensity (WMHV) and total hippocampal volume (THV), and assess whether these associations were influenced by sex, age or cardiometabolic factors. Results: Complete data were available for 22,199 individuals (mean age 64 years [SD 7], 64% women). In univariable analyses, lower CI was associated with lower TBV, GMV, WMV, THV and greater WMHV (p < 0.001). In adjusted models, statistically significant CI × age interactions were observed for TBV, GMV, and THV (all p < 0.01) indicating more pronounced associations in older individuals. No CI × sex interactions were identified. Conclusions: Lower cardiac index is associated with lower brain volumes and greater vascular lesion burden in mid-to later life, with evidence of age modification for TBV, GMV and THV.