EFFECT OF A SINGLE-DOSE OF DIAZEPAM ON BALANCE MEASURES IN OLDER-PEOPLE

OBJECTIVE: This study examines the effect of a single dose of diazepam on a spectrum of balance measures in healthy older subjects. The meas ures include static (postural sway), dynamic (anterior tibialis muscle activation latency), and a complex self-initiated task of balance (fu nctional reach) in addition to neuropsychological tests of attention. DESIGN: A double-blind, two-period, cross-over trial. SETTING: The com munity surrounding a university hospital. PARTICIPANTS: Community-dwel ling, nonsmoking volunteers 65 years of age and older MEASUREMENTS: Me asures included response to unexpected perturbation (platform/EMG musc le latency), self-initiated perturbation (functional reach), and a sta tic measure of balance (postural sway). Neurocognitive tests (digital symbol substitution test, card sorting) were included to document the cognitive effect. RESULTS: Twelve nonsmoking healthy subjects (average age = 70.4 years (66-76 years)) participated. The anterior tibialis m uscle latency increased in response to a sudden perturbation with diaz epam compared with placebo (TA latency 149 ms vs 142 ms, P < .001). Ne urocognitive tests were adversely affected for 90 minutes after diazep am administration compared with placebo (P < .05). Other measures did not demonstrate significant effect of diazepam. CONCLUSIONS: This is a mong the first reports showing that benzodiazepines affect neuromuscul ar processing related to balance control. Increased muscle latency to sudden perturbations may represent an effect of diazepam upon the olig osynaptic spinal reflex distinct from the sedation. Surface electromyo graphy may be a valuable noninvasive tool for future studies of drug e ffect on balance and falls risk among older people.