Bioimpedance Analysis to Determine the Effect of Pressure Release on Limb Fluid Volume Change in Persons with Transtibial Limb Loss

Thesis (Master's)--University of Washington, 2012INTRODUCTION: Over 1 million Americans currently live with a lower limb amputation. Lower limb prostheses have been designed to produce a secure and comfortable fit between residual limb and prosthesis throughout the day. However, significant fluid volume fluctuations in the residual limb deteriorate socket fit and may cause decreased mobility due to discomfort or soft tissue injury from increased pressures and shear stresses. Extracellular fluid is thought to be the primary source of limb volume fluctuation and commonly decreases over the course of the day. Technologies designed to address limb fluid volume loss are ineffective and cumbersome. Methods to assess limb fluid volume change are also poor, lacking the capability to quantify fluid volume loss at high temporal resolution and while the prosthesis is donned. METHODS: Bioimpedance analysis provides tools to rapidly estimate extracellular fluid volume while a subject performs regular activity with the prosthesis donned. Using a custom bioimpedance analyzer, we tested 16 subjects each on three separate occasions in a repeated measures study. Each test session consisted of an activity sequence followed by a 30 minute period of calm sitting (dubbed the recovery sit). During the recovery sit, subjects sat with their prosthesis donned (ON), prosthesis doffed (OFF), or liner donned (LINER). An identical activity sequence followed the 30 minute sit. RESULTS: Volume changes during the OFF 30 minute recovery sit were significantly higher than during ON (p < 0.001). We observed that after the limb gained fluid volume during the OFF protocol, subsequent volume loss was negligible in 12 of 16 subjects during the following activity sequence. Conversely, volume lost during the 30 minute recovery period during ON was not recovered during three cycles of activity. During the LINER protocol, volume gains during the 30 minute sit were similar to those during OFF, but returned to baseline levels during subsequent activity. Gains in LINER during subsequent activity still remained elevated as compared to ON (p < 0.01). CONCLUSIONS: Decreasing applied pressure to the residual limb may function to recover limb fluid volume, allowing socket users to maintain a comfortable fit between limb and prosthesis. There exists a potential for development of socket technology that leverages pressure release to recover limb fluid volume