Analysis of thermal properties of wheelchair cushions with thermography

Thermal properties of wheelchair cushions have been traditionally studied with thermistor probes, which provide temperature values of limited areas (spot analysis). In this paper, we describe a novel procedure based on thermography for assessing the distribution of temperature over the entire surface of wheelchair cushions. The thermal transient during contact with the body (heating phase) and after use (cooling phase) is considered. The procedure was tested in four different seat cushions (with a gel pad, air-filled cells, gel-filled bubbles and foam-filled bubbles) used by a normal subject. Observed results were compatible with the predicted outcomes based on an analysis of the materials and structures. Specifically: (i) air-filled cushions exhibited the fastest thermal transients, gel cushions the slowest transients, while cushions with a mixed structure exhibited intermediate behaviour; (ii) cushions made from flat surfaces of foam exhibited the highest peak temperatures (30.8°C) as compared to those with air-filled cells (30.35°C) or bubble-shaped surfaces (29.7°C); (iii) the average temperature under the thighs was significantly higher than that under the ischiatic area in all cushions (29.6°C compared with 28.7°C, p<0.05). It is shown that the present method can be used to differentiate between different cushions. Although the ‘macro-analysis’ inherent in thermography appears to be suited for improving cushion design, this approach should be further investigated to determine its reliability.