Association between heart rate variability and brain glucose metabolism in healthy middle‐aged men

This study aimed to assess the association between brain glucose metabolism, measured using 2‐deoxy‐2‐[18F]fluoro‐ d ‐glucose positron emission tomography/computed tomography ( 18 F‐FDG PET/CT), and heart rate variability (HRV). A total of 101 healthy men were included. Each participant underwent the following assessments: (1) brain 18 F‐FDG PET, (2) anthropometric measurements, and (3) HRV test. PET scans were spatially normalised to MNI space using PET templates from SPM5 with pmod. An Automated Anatomical Labelling 2 atlas was used to define regions of interest (ROIs). For each ROI, the mean uptake was normalised to the individual's global cortical mean uptake, yielding a standardised uptake value ratio (SUVR). After logarithmic transformation of the regional SUVR, the effects of the root mean square of successive differences (RMSSD) on the regional SUVR were investigated using Bayesian hierarchical modelling. Our main finding was that RMSSD of 101 middle‐aged males was positively associated with brain glucose metabolism in occipital lobe, parietal lobe, precuneus, and cuneus. A negative association was observed in the cerebellum, thalamus, and parahippocampus. These findings suggest that brain regions associated with psychiatric disorders and cognitive and affective functions are associated with parasympathetic activity, as measured by the RMSSD. This study provides new insights into the mechanisms regarding autonomic nervous system.