The aim of the study was to evaluate the efficiency of a position/activity monitoring system based on a dual-axis accelerometer strapped to the subject's thigh and a position sensor located within a monitor placed on the subject's belt.
Twenty-six subjects wearing two monitors (one accelerometer on each thigh) were submitted to various activities and positions under the control of an observer. An analysis of each tracing was performed both manually by a technician and automatically by dedicated software before being compared with the information gathered during the study.
The accelerometer allowed accurate discrimination between the standing versus the sitting and lying positions. The sitting and lying positions were correctly detected by the built-in position sensor provided the unit was firmly attached. Walking was adequately detected by the accelerometer. The activity score was well correlated with treadmill speed. Changes in position and activity were detected with a mean error of less than 3 s.
The combination of an accelerometer placed on the subject's thigh and a position sensor located at the subject's waist appeared to be a suitable system for position/activity monitoring during ambulatory ECG and blood pressure monitoring.
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Received 14 February 2003 Revised 16 July 2003 Accepted 21 October 2003