Synergistic experimental and numerical characterization of a dry-heat, fluid-warming device.

Fluids that are infused into the human body must be at a temperature that is compatible with the internal thermal state of the body. Since infusants are typically stored at temperatures that are too low for compatibility, a heating means is required to achieve the appropriate infusion temperature. This paper sets forth a synergistic investigation involving coupled experimentation and numerical simulation of the characteristics of one of the main categories of body-fluid heating means. The methodology developed here serves equally well as a design optimization tool. The paper encompasses two stages: (a) an experimental and numerical evaluation of a generic warming device in common use and (b) a redesign utilizing the same tools to elevate the performance of devices of this category. The numerical simulation dealt with steady and unsteady three-dimensional fluid flow and heat transfer which are endemic to devices of this kind. The two-pronged approach developed here was shown to be capable of coping with an operating feature called stopflow wherein an officiating physician orders an immediate cessation of fluid flow. The thermal events following stopflow are well described by the numerical simulations.

Rationalization of thermal injury quantification methods: application to skin burns.

Classification of thermal injury is typically accomplished either through the use of an equivalent dosimetry method (equivalent minutes at 43 °C, CEM43 °C) or through a thermal-injury-damage metric (the Arrhenius method). For lower-temperature levels, the equivalent dosimetry approach is typically employed while higher-temperature applications are most often categorized by injury-damage calculations. The two methods derive from common thermodynamic/physical chemistry origins. To facilitate the development of the interrelationships between the two metrics, application is made to the case of skin burns. This thermal insult has been quantified by numerical simulation, and the extracted time-temperature results served for the evaluation of the respective characterizations. The simulations were performed for skin-surface exposure temperatures ranging from 60 to 90 °C, where each surface temperature was held constant for durations extending from 10 to 110 s. It was demonstrated that values of CEM43 at the basal layer of the skin were highly correlated with the depth of injury calculated from a thermal injury integral. Local values of CEM43 were connected to the local cell survival rate, and a correlating equation was developed relating CEM43 with the decrease in cell survival from 90% to 10%. Finally, it was shown that the cell survival/CEM43 relationship for the cases investigated here most closely aligns with isothermal exposure of tissue to temperatures of ~50 °C.

Surrogate human tissue temperatures resulting from misalignment of antenna and implant during recharging of a neuromodulation device.

OBJECTIVES: A synergistic experimental and numerical investigation has provided quantitative information on the response of surrogate human tissue temperatures to misalignment of the implant and antenna of neuromodulation devices during recharging. MATERIALS AND METHODS: The experimental phase of the work provided information on the rates of heat transfer from the implant and the antenna to their respective surroundings. The heat transfer data were used as input to a biothermal model from which tissue temperature distributions were obtained. RESULTS: It was found that misalignment increases tissue temperatures compared with those for the aligned case for all of the investigated devices. These increases ranged from 0.5°C to 5.3°C. CONCLUSION: Notwithstanding these increases, the lowest temperatures were attained by the Restore Ultra device for all operating conditions. The temperature levels achieved by the Precision Plus and Eon Mini devices were found to be greater than those for the Restore Ultra but their relative rankings depend on the thermal boundary conditions and the duration of the recharging period. The foregoing rank ordering was validated by a sensitivity study in which the heat transfer data inputted to the numerical simulation was varied systematically. The aforementioned comparisons correspond with identical recharging periods for all of the devices.