LEIPZIG, Germany — A novel, noninvasive method can assess changes to residual limb skin health and circulation in response to elevated vacuum suspension, according to data presented here.
“These techniques leverage out-of-socket skin health measurements, out-of-socket circulation imaging, and in-socket, probe-based circulation measurements,” Matthew Wernke, PhD, research engineer with WillowWood said at the OT World Congress. “This work represents the first efforts to quantitatively assess changes in the residual limb in response to vacuum.”
Wernke presented feasibility data from one patient, in whom researchers took measurements using suction and elevated vacuum suspension (EVS) during activity and pre-activity and post-activity, at baseline, 8 weeks and 16 weeks.
The first measurement taken before activity is transepidermal water loss, which indicates epidermal barrier function. The probe is placed on the skin and shows the difference between ambient room humidity and the relative humidity above the skin.
“Preliminary data shows the amount of water loss is a little higher immediately after removing the socket compared to after the limb has set out and aired for 15 minutes,” Wernke said.
The second measurement is skin surface electrical capacitance, a measure of moisture on the skin. Similarly, this measurement revealed more moisture on the skin immediately after removing the socket.
More direct skin health measurements included cutometry, which measures skin elasticity. A probe is placed on the skin and applies a negative pressure, which allows for real-time measurement of the flexion of the skin. Results showed a reduced viscoelastic modulus and increased reaction time compared with non-amputee participants.
The last direct measurement of skin health is torsional ballistometry, which quantifies the hardness and elasticity of the skin. A pin is dropped from a known height onto the skin surface.
“We get two bits of information from this. First, the indentation depth is inversely proportional to the skin softness. And the speed at which that oscillation dampens out is inversely proportional to elasticity,” Wernke said.
These measurements were expected to vary between patients, he said.
Out-of-socket circulation measurements were performed before and after activity. The first measurement is hyperspectral imaging, which creates a map of local oxygen delivery and extraction within the tissues, Wernke said. Compared with a non-vacuum socket, EVS on nearly eliminated reactive hyperemia in the residual limb, indicating a steady blood flow.
“Where this is exciting for us, is now you see this difference pre-activity and post-activity for the residual limb is no longer present. From this initial data from one patient it seems that elevated vacuum suspension eliminates this reactive hyperemia,” Wernke said.
The other out of socket circulation measurement is laser speckle imaging. Laser light illuminates the tissues, which produces a reflection that changes based on blood perfusion. Post-activity measurement revealed high reactive hyperemia in the residual limb in the non-vacuum socket, but in the elevated vacuum socket, reactive hyperemia was reduced.
Three in-socket circulation measurements were performed in real-time: temperature, laser Doppler flowmetry, and transcutaneous oxygen measurement (TCON). Within the elevated vacuum suspended socket at baseline and at 8 weeks, TCON measurements showed an increase in tissue oxygenation during activity, “which shows some benefits of using vacuum for a long period of time,” Wernke said.
Perfusion measurements pre-activity and post-activity at 8 weeks of using vacuum showed steady perfusion. Researchers are currently conducting a randomized crossover study of five transfemoral and five transtibial amputees using suction and EVS conditions using these methods, he said. — by Carey Cowles
For more information:
Wernke M. Methodological assessment of residual limb circulation and skin health in response to elevated vacuum suspension. Presented at: OT World Congress; May 12-16, 2014; Leipzig, Germany.
Disclosure: Wernke is employed by WillowWood, which produces a vacuum suspension system.