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Pressure mapping

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Interface pressure mapping involves using sensors to quantify the pressure between two contacting objects, such as a person and their support surface. Pressure mapping has many wide spread applications, but in assistive technology it is commonly used by clinicians to determine the suitability of a wheelchair cushion and by researchers investigating support surfaces, risk factors for ulceration, and ulcer prevention protocols. Pressure mapping systems can be made in many configurations for different uses but the most commonly encountered clinically are the thin mats used by seating specialists. These mats are approximately 18” by 18” and are composed of a matrix of small sensors and a cover. When a person sits on such a mat, the sensors read pressure at individual locations on the thigh or buttock. This data is transferred to a computer where a clinician can analyze it. Evenly distributed pressure is preferred. High peaks surrounded by low pressure are undesired, as this may indicate that a bony prominence, such as an ishial tuberosity, is carrying considerably more load than the surrounding tissues. High values overall are also unwanted, but the distribution of pressure is more important as magnitude can be affected by sensor factors such as calibration. Pressure mapping is most useful for comparing support surfaces in one day. Day to day comparisons are difficult to make unless the mats are calibrated frequently and a controlled protocol is followed in data collection.

Several different companies make pressure mapping systems. They differ in the technology used, the size of the sensors, and the number of sensors in the array. Most thin flexible pressure sensors either use resistive or capacitive sensor technology. Some of the most common are described below.


FSA - Force Sensing Array by Vista Medical

FSA mats have up to 1024 resistive sensors. Each sensor is composed of two pieces of conducting material separated by a material whose resistance changes as force is applied. During calibration, the output resistance is correlated to a known pressure.


Tekscan also uses resistive technology, but the resistive material used in Tekscan sensors is a semi-conductive ink. Flexible polyester sheets laid out in a series of rows and columns sandwich the resistive ink. The intersection of a row, a column, and the resistive ink makes up 1 sensor. The Tekscan Conformat stretches to conform to the surfaces being tested, reducing hammocking. Hammocking is when a mat introduces error because the tension on it hinders immersion and envelopment. A Conformat has 1024 sensors.


XSensor pressure sensors are capacitive and cloth-like. Their seating mat is made up of 1296 sensors. Calibration for XSensor mats is done 2-3 times per year by the company instead of by the user.


Author: Leigh Pipkin
Affiliation: CATEA at Georgia Tech