Simulation of a cold-stressed finger including the effects of wind, gloves, and cold-induced vasodilatation

摘要

The thermal response of fingers exposed to cold weather conditions has been simulated. Energy balance equations were formulated, in a former study, for the tissue layers and the arterial, venous, and capillary blood vessels. The equations weresolved by a finite difference scheme using the Thomas algorithm and the method of alternating directions. At this stage of development the model does not include any' autonomic control functions. Model simulations assumed an electrical heating element tobe embedded in the glove layers applied on the finger. A 1.3 W power input was calculated for maintaining finger temperatures at their pre-cold exposure level in a 0℃environment. Alternate assumptions of nutritional (low) and basal (high) blood flows inthe finger demonstrated the dominance of this factor in maintaining finger temperatures at comfortable levels. Simulated exposures to still and windy air, at 4.17 m/s (15 km/h), indicated the profound chilling effects of wind on fingers in coldenvironments. Finally, the effects of variable blood flow in the finger, known as "cold-induced vasodilatation," were also investigated Blood flow variations were assumed to be represented by periodic, symmetric triangular waves allowing for gradualopening-closing cycles of blood supply to the tip of the finger. Results of this part of the simulation were compared with measured records of bare finger temperatures. Good conformity was obtained for a plausible pattern of change iii blood flow, whichwas assumed to be provided in its entirely' to the tip of the ,finger alone.