Personal Cooling Strategies for Alleviating the Thermal Strain of People with Spinal Cord Injury

Abstract

People with spinal cord injury (SCI) are prone to thermal strain (i.e. unsafe elevation in body core temperature) at hot conditions and/or high metabolic rates resulting in various levels of thermal discomfort based on injury level. This is due to the loss of motor/sensory functions at impaired body segments and disruption in both sweating and vasodilation responses. Therefore, for the health and well-being of people with SCI, it is of interest to investigate different personal cooling strategies. In literature, conventionally used phase change material (PCM) and evaporative cooling vests (ECVs) succeeded in reducing thermal strain for able-bodied people, but its application for people with SCI is still scarce and not conclusive in literature. Therefore, in this research, it is aimed to assess the effect of these two types of cooling vests on the physiological and psychological responses of people with SCI at different ambient conditions and metabolic rates. To achieve this goal, research methodology tracked two approaches; modelling and experimentation to assess the performance of proposed cooling vests for persons with SCI, and consequently, provide recommendations about the optimal design and use of these cooling strategies at different ambient conditions and physical activity levels.

To assess cooling vest performance, multi-segmented bioheat models for persons with SCI that can predict core and skin temperature values were developed and validated via previous studies in literature. Then, published fabric-PCM 1D-transient mathematical model was integrated into the bioheat model of person with SCI to predict the effect of PCM cooling vest on body core and skin temperatures as well as heat losses from sensate and insensate skin of the trunk. Validation of the developed combined model was done via previous studies in literature, and a parametric study about coverage area on the sensate/insensate skin of trunk and melting temperature of PCM cooling vest was done. Based on the findings of model predictions, human subject experiments were completed to test the proposed improvements in the design of PCM cooling vest for persons with SCI during exercise in heat.

Since PCM cooling vests caused additional weight burden and restricted movement of persons with SCI, the use of evaporative cooling vest (ECV) incorporated with ventilation fans (hybrid vest) is proposed to enhance heat losses at the limited sensate trunk skin area of person with PA. A 1-D transient mathematical model for the hybrid vest was developed and integrated with the validated PA-bioheat model to predict body thermophysiological responses. The hybrid vest model was validated via experiments performed on a heated plate. A parametric study was then performed using the integrated models at range of ambient temperature and relative humidity for moderate and high activity levels. Evaluation of the hybrid ECV performance for persons with PA was based on the drop in local sensate skin, and sensible and latent heat losses, compared to No-Vest case. Furthermore, human subject experiments were done to evaluate the physiological and psychological responses of patients with SCI when using a commercially available of ECV.