Pressure and Motion Characteristics of Weight Relief Activities to Prevent Skin Breakdown in the Sensorimotor Impaired

Eric E. Sabelman, PhD; Ruth Yap, MS; Carolyn Keeler, BA; Elizabeth Placek, BA

Objectives: We are investigating new methods for individuals at risk for pressure sores (decubitus ulcers) to self-monitor training and routine performance of pressure relief and transfer activities, and to provide a variety of real-time visual, tactile and/or auditory cues to the user when pressure or inactivity limits have been exceeded. The simplest means for prevention of skin breakdown is periodically redistributing body weight, but poor compliance with self-performed or assisted weight relief or turning in bed can still lead to skin lesions.

Methods: We have designed a Wearable Accelerometric Motion Analysis System ("WAMAS") consisting of 3-axis motion sensors, in this case placed on a belt above each hip, along with a self-contained data acquisition computer. Flat pressure-sensing balloons were added, located under the body at a distance from probable sites of skin breakdown (e.g.: mid-thigh). Five chronic spinal cord injury subjects were asked to perform repeated weight relief (arm push-up, forward, oblique and lateral lean) activities on two occasions.

Results/Conclusions: Interface pressure and body motion data were analyzed to extract characteristics identifying correct and incorrect weight shift activities. Uniaxial accelerations were converted to lateral ("AZY") and forward ("AZX") waist tilt angles; change in 3-second rolling standard deviation was used to detect start of an activity. Activities were distinguished by Boolean sum of angle, pressure, and time after start relative to pre-start: {DA_n<>a_n AND DP_n <> b_n AND t <> t_n ANDNOT DA_m<> a_m ANDNOT DP_m <> b_m}, where a, b, and t are threshold values of n variables which must cross thresholds and m variables which must not pass thresholds. In the examples shown, correctly-performed right lean requires right (RB) and left (LB) AZY to decrease at least -10° while left pressure decreases at least -5 mm Hg for t >15 seconds. Forward lean requires RB and LB AZX angles and thigh pressure all to increase bilaterally.

Clinical Relevance: Sensorimotor impaired veterans need assistance to prevent skin breakdown. If caregiver time is limited, the WAMAS can act as a surrogate, monitoring motion status and compliance with a course of therapy. We expect that in-home unattended use of the WAMAS programmed with time, pressure and motion thresholds customized to the individual can alleviate excess pressure leading to skin breakdown.

Acknowledgments: VA RR&D merit review project E2153TC; VA Palo Alto Rehabilitation R&D Center core support.