The effect of posture on the age dependence of neurovascular coupling.

Previous studies report contradicting age-related neurovascular coupling (NVC). Few studies assess postural effects, but less investigate relationships between age and NVC within different postures. Therefore, this study investigated the effect of age on NVC in different postures with varying cognitive stimuli. Beat-to-beat blood pressure, heart rate and end-tidal carbon dioxide were assessed alongside middle and posterior cerebral artery velocities (MCAv and PCAv, respectively) using transcranial Doppler ultrasonography in 78 participants (31 young-, 23 middle- and 24 older-aged) with visuospatial (VST) and attention tasks (AT) in various postures at two timepoints (T2 and T3). Between-group significance testing utilized one-way analysis-of-variance (ANOVA) (Tukey post-hoc). Mixed three-way/one-way ANOVAs explored task, posture, and age interactions. Significant effects of posture on NVC were driven by a 3.8% increase from seated to supine. For AT, mean supine %MCAv increase was greatest in younger (5.44%) versus middle (0.12%) and older-age (0.09%) at T3 (p = 0.005). For VST, mean supine %PCAv increase was greatest at T2 and T3 in middle (10.99%/10.12%) and older-age (17.36%/17.26%) versus younger (9.44%/8.89%) (p = 0.004/p = 0.002). We identified significant age-related NVC effects with VST-induced hyperactivation. This may reflect age-related compensatory processes in supine. Further work is required, using complex stimuli while standing/walking, examining NVC, aging and falls.