Older Adults' Drop In Cerebral Oxygenation On Standing Correlates With Postural Instability And May Improve With Sitting Prior To Standing

Background: Impaired blood pressure (BP) recovery with orthostatic hypotension on standing occurs in 20% of older adults. Low BP is associated with low cerebral blood flow but mechanistic links to postural instability and falls are not established. We investigated whether posture-related reductions in cerebral tissue oxygenation (tSO(2)) in older adults impaired stability upon standing, if a brief sit before standing improved tSO(2) and stability, and if Low-tSO(2) predicted future falls.Method: Seventy-seven older adults (87 +/- 7 years) completed (i) supine-stand, (ii) supine-sit-stand, and (iii) sit-stand transitions with continuous measurements of tSO(2) (near-infrared spectroscopy). Total path length (TPL) of the center of pressure sway quantified stability. K-cluster analysis grouped participants into High-tSO(2) (n = 62) and Low-tSO(2) (n = 15). Fall history was followed up for 6 months.Results: Change in tSO(2) during supine-stand was associated with increased TPL (R = -.356, p = .001). When separated into groups and across all transitions, the Low-tSO(2) group had significantly lower tSO(2) (all p < .01) and poorer postural stability (p < .04) through 3 minutes of standing compared to the High-tSO(2) group. There were no effects of transition type on tSO(2) or TPL for the High-tSO(2) group, but a 10-second sitting pause improved tSO(2) and enhanced postural stability in the Low-tSO(2) group (all p < .05). During 6-month follow-up, the Low-tSO(2) group had a trend (p < .1) for increased fall risk.Conclusions: This is the first study to show an association between posture-related cerebral hypoperfusion and quantitatively assessed instability. Importantly, we found differences among older adults suggesting those with lower tSO(2) and greater instability might be at increased risk of a future fall.