A Novel Cooling Wheelchair Design as a Proof-Of-Concept Study

Background: For many wheelchair users, the combination of reduced mobility and impaired sensation, including but not limited to neurological insults, vascular issues, decreased cognition, and morbid obesity, results in a life-time risk of pressure ulcer development. Pressure ulcers are a type of wound that results from a breakdown of tissue over bony prominences due to localized ischemia caused by constant pressure. The compromised blood circulation along with reduced airflow results in an accumulation of heat in the tissue over the bony prominence which accelerates the tissue breakdown. In recent years, wheelchair cushions employed thick foam type materials, which provided a higher quality of pressure distribution but poorer heat dissipation. Purpose: In this study, we designed a custom-built cushion that circulated chilled water. We measured buttocks surface temperatures and peak pressures around the ischial tuberosity, with a targeted maximum temperature and pressure of 28°C and 60mmHg, respectively. Methods: In this ongoing study, we recruited one subject so far. The subject was asked to sit and actively propel the wheelchair with the aforementioned cushion for 30 minutes. Thermal images of the participant’s buttocks were collected before and after wheelchair use and temperatures were collected in 10 minute intervals while seated, using thermocouples (K-type). Pressure distribution was captured at the end of the wheelchair use using a Tekscan ConforMat, which was placed on top of the cooling cushion. All study procedures were approved by the institutional review board (IRB) prior to recruitment and testing, and informed consent was obtained from subjects prior to testing. Results: The results indicated that the cooling wheelchair cushion was capable of cooling the tissue from 28.1°C to 24.9°C. The chilled water temperature ranged from 21.5-21.8°C during wheelchair use. Peak pressure occurred at the right ischial tuberosity and was quantified as 115mmHg. Conclusions: The custom-built cooling wheelchair cushion maintained temperatures of the buttocks below 28°C but failed to lower the peak pressure to below 60 mmHg. Further modification and testing of the cushion design are warranted to achieve the pressure reduction goal. Another improvement will be adding a closed-loop control system to prevent overcooling of the tissue.