Thermal response of skin to cyclic pressure and pressure with shear: a technical note.

The thermal response of skin to pressure alone and to pressure with shear was compared under cyclic loading conditions. Stresses were applied to the anterior aspect of the leg of three healthy subjects for time intervals up to 10 min, and the difference in temperature between the stressed site and a contralateral control site was assessed after load release. The thermal recovery time (TRT), the time interval between load release and either a maximum or a stabilization in the temperature difference vs. time record was determined. Results demonstrated that for a resultant stress of 142.9 kPa, TRTs were longer for combined pressure and shear than for pressure alone. For Subjects A, B, and C, TRT increases were 1.5 min, 5.5 min, and 2.0 min respectively. For a resultant stress magnitude of 71.4 kPa, increases were 1.5 min, 3.5 min, and -0.5 min respectively. Comparing responses for different resultant stress magnitudes for pressure-only application, TRTs were 1.5 min, 1.5 min, and 5.5 min longer for the 142.9-kPa condition than for the 71.4-kPa condition for Subjects A, B, and C. For combined pressure and shear, increases were 1.5 min, 3.5 min, and 8.0 min respectively. A next step will be to determine if the TRT differences measured here are physiologically relevant and have clinical meaning. The thermal response assessment method could then potentially be used to quantitatively evaluate the effects of different interface design features in lower-limb prosthetics on tissue response.