Quantitative Measurement of the Pressure and Shear Stress Acting on the Body of a Wheelchair User Using a Wearable Sheet-Type Sensor: A Preliminary Study.

To provide a safer sitting environment for wheelchair users, it is important to quantitatively measure the forces acting on the contact surface between the seat and the person in the wheelchair. In addition to the pressure acting on the buttocks, shear forces have received particular attention in recent years; however, measuring shear force is more difficult than measuring pressure. To obtain this measurement, a thin and flexible sensor that can be used in a natural state on a wheelchair is needed. Therefore, we constructed a measurement system using our previously developed wearable sheet-type sensor (0.9 mm thick). In this study, preliminary tests were conducted using human dummies before testing on humans. Sensors were placed in four locations on the humanoid dummy's back and buttocks, and the electric wheelchair was tilted and reclined five times each. The results showed that the sensor output pattern was reproducible and valid enough to proceed to the next step. However, the shear force in the internal and external directions was greater than expected, which indicates that the equipment and testing methods must be reviewed. On the basis of the results obtained in this preliminary study, preparations will be made for testing on human subjects.

The relationship between torso inclination and the shearing force of the buttocks while seated in a wheelchair: Preliminary research in non-disabled individuals.

The shearing force acting upon the contacting surface of the buttocks while seated in a wheelchair has been linked to the development of pressure ulcers. However, the actual causative factors have not been examined in detail. In an attempt to clarify the nature of this problem, we developed a specific measurement system. In preparation for future clinical applications, we conducted preliminary testing in non-disabled individuals. As a result, we were able to discover a number of issues related to this system and our measurement methods. Although we only evaluated a limited number of typical sitting postures, we were able to record the buttocks shearing force reference values for non-disabled individuals. Our results suggest that regardless of posture, a backward-directed shearing force occurs below the ischial tuberosity in non-disabled individuals in seated positions. This force seemed to increase as the individual leaned forward. Meanwhile, tilting the torso to one side seemed to be associated with an increase in the shearing force working in the opposite direction. We hope that these findings can be utilized for reference purposes in future research among non-disabled individuals.

Provision of public funding for wheelchairs and postural support devices in Japan.

[Purpose] For people with disabilities, public funding is the principal means by which assistive devices, such as wheelchairs and seating equipment, may be acquired. In the future, to make the system easier for beneficiaries, it is necessary to determine the actual utilization level in the current system. In this study, using statistical data provided by the Japanese government, we investigated the level of public expenditure on wheelchairs and postural support devices. [Methods] The number of devices (Wheelchairs, Powered Wheelchairs, Postural Support Devices, and Seating Furniture) provided each year from 1997 to 2016 was extracted and the annual trends were analyzed. [Results] In the last 20 years, the number of grants provided for wheelchairs has decreased, while the number of grants provided for seating equipment has increased. These changes may be due to the enactment of new legislation. [Conclusion] Based on the anticipated service life of various types of equipment, it is believed that approximately 970,000 assistive devices in the four categories are provided with public funding alone. As the number of people with disabilities increases, the use and importance of assistive devices is also expected to increase.

Development of Wearable Sheet-Type Shear Force Sensor and Measurement System that is Insusceptible to Temperature and Pressure.

A sheet-type shear force sensor and a measurement system for the sensor were developed. The sensor has an original structure where a liquid electrolyte is filled in a space composed of two electrode-patterned polymer films and an elastic rubber ring. When a shear force is applied on the surface of the sensor, the two electrode-patterned films mutually move so that the distance between the internal electrodes of the sensor changes, resulting in current increase or decrease between the electrodes. Therefore, the shear force can be calculated by monitoring the current between the electrodes. Moreover, it is possible to measure two-dimensional shear force given that the sensor has multiple electrodes. The diameter and thickness of the sensor head were 10 mm and 0.7 mm, respectively. Additionally, we also developed a measurement system that drives the sensor, corrects the baseline of the raw sensor output, displays data, and stores data as a computer file. Though the raw sensor output was considerably affected by the surrounding temperature, the influence of temperature was drastically decreased by introducing a simple arithmetical calculation. Moreover, the influence of pressure simultaneously decreased after the same calculation process. A demonstrative measurement using the sensor revealed the practical usefulness for on-site monitoring.

A preliminary study of the measurement of overload applied to the foot support of a wheelchair and a seated postural support device.

[Purpose] The mechanical strength of wheelchair and seating products is specified by standards to ensure user safety. However, some individual users are affected by severe spasticity resulting from cerebral palsy that occasionally breaks such devices. Until recently, reports of quantitative measurement of these mechanical overloads have been scarce, and the exact loads applied have been unknown. This study aimed to conduct a sampling survey prior to conducting a future full-scale study. [Subjects and Methods] Using two force plates, we measured the load on the foot support applied by three participants with cerebral palsy. The applied load was measured at a 100 Hz sampling rate, and maximum load and vertical/horizontal component forces were analyzed. [Results] The maximum load applied by participants was approximately 1.34 times their body weight. The vertical force applied on the foot support accounted for 70-80% of the total load. The horizontal force also reached about 35% at its maximum. [Conclusion] Because the horizontal load also reached 1/3 of the total load, it will be advantageous to use a three-axis force plate to measure forces in a future study with more participants.