A NOVEL TOOL TO QUANTIFY PHYSICAL ACTIVITIES - AMBULATORY ACCELEROMETRY IN PSYCHOPHARMACOLOGY

Accelerometry by means of body-mounted piezoresistive sensors was eval uated as a new method to quantify physical activities (body posture an d physical and locomotor activity) in relation to the sedative and car diovascular effects of benzodiazepines, in an ambulatory study. In a d ouble-blind, randomized, crossover study, 12 healthy men received eith er an oral dose of 2 mg lorazepam, 0.5 mg alprazolam, 1 mg alprazolam, or a placebo on 4 different days. By means of a portable digital reco rder, each day 4 hours of continuous measurements of accelerometer sig nals and heart rate were performed in a living room in the hospital. C hanges in subjective sleepiness were assessed at the beginning, halfwa y, and at the end of the recording period. A separate validation study of the ambulatory environment was performed in three subjects, in whi ch computer classification of activities based on accelerometry was co mpared with visual evaluation of simultaneously recorded videotapes. I n our validation study, comparison of the computer classification with visual analysis based on videotapes revealed an overall agreement for spontaneous and standardized activities of 88% and 96%, respectively. In our pharmacological study, the subjects spent more time in the lyi ng position (p < 0.01) and less time in the sitting position (p < 0.01 ) after benzodiazepine administration; the effects were strongest for lorazepam. Motility during static activities was reduced (p < 0.025), with motility after lorazepam administration being lowest. Both loraze pam and alprazolam (0.5 and 1 mg) increased subjective sleepiness (p < 0.01). On average, lorazepam induced an overall increase in mean hear t rate of about 6%, whereas alprazolam reduced mean heart rate by 2% v ersus placebo (p < 0.01); the effects were not dependent on posture. T he validation study showed that accelerometry forms a reliable method to quantify aspects of normal daily activities. Our pharmacological st udy revealed that quantification of body postures, physical activity, and motility by means of ambulatory accelerometry proves to be an obje ctive and promising tool to evaluate the psychological and cardiovascu lar effects of (psyche) pharmaca in relation to the postural and mobil ity activities of normal daily life.