Hemodynamic and structural brain measures in high and low sedentary older adults

Abstract

Due to its cardiovascular effects sedentary behaviour might impact cerebrovascular function in the long term, affecting cerebrovascular regulatory mechanisms and perfusion levels. Consequently this could underly potential structural brain abnormalities associated with cognitive decline. We therefore assessed the association between sedentary behaviour and brain measures of cerebrovascular perfusion and structural abnormalities in community-dwelling older adults. Using accelerometery (GENEActiv) data from The Irish Longitudinal Study on Ageing (TILDA) we categorised individuals by low- and high-sedentary behaviour (≤8 vs >8 hours/day). We examined prefrontal haemoglobin oxygenation levels using Near-Infrared Spectroscopy during rest and after an orthostatic challenge in 718 individuals (66 ± 8 years, 52% female). Global grey matter cerebral blood flow, total grey and white matter volume, total and subfield hippocampal volumes, cortical thickness, and white matter hyperintensities were measured using arterial spin labelling, T1, and FLAIR MRI in 86 individuals (72 ± 6 years, 55% female). While no differences in prefrontal or global cerebral hemodynamics were found between groups, high-sedentary individuals showed lower hippocampal volumes and increased white matter hyperintensities compared to their low-sedentary counterparts. Since these structural cerebral abnormalities are associated with cognitive decline and Alzheimer's disease, future work exploring the causal pathways underlying these differences is needed.

Keywords: Alzheimer’s disease; cognitive decline; hemodynamics; neuroimaging; sedentary behaviour.

Figure 1.

Flow chart sample.

Figure 2.

Hemodynamic response during active stand. Results shown are TSI change from baseline (%) during active stand for participants with more or less than eight hours of SB a day from model 2, corrected for age, sex, education, height, standing time, smoking, alcohol use, BMI, cardiovascular conditions, AHD use, and depression. N = 716 due to 2 cases with missing BMI.

Figure 3.

Estimated marginal means of low- and high-SB for six MRI outcome measures. Results represent the estimated marginal means (95% CI) of less (low-SB) or more (high-SB) than eight hours of SB a day. Model 1 corrected for age, sex, education, and eTIV (only for grey matter, white matter, and hippocampal volume). Model 2 additionally corrected for smoking, alcohol use, BMI, cardiovascular conditions, AHD use, and depression. A grey matter volume, B hippocampal volume, C grey matter CBF, D white matter volume, E cortical thickness, F WMHs. Model 1 N=86, Model 2 N=85. *significant p<0.05, ^#trend p<0.10.

Figure 4.

Estimated marginal means of low- and high-SB for hippocampal subfield volumes. Results represent the estimated marginal means (95% CI) of less (low-SB) or more (high-SB) than eight hours of SB a day for the volumes of eleven hippocampal subfields from model 1, corrected for age, sex, education, eTIV. N=86. *significant p<0.05, ^#trend p<0.10.