Assessment of alternating air mattresses using a time-based interface pressure threshold technique.

Laboratory evaluation techniques for support surfaces have centered largely around interface pressure (IP) measurement, typically analyzing discrete maximum and minimum levels, or calculating the average pressure. Nowadays, alternating pressure air mattresses (APAMs) are used increasingly for the prevention and treatment of pressure sores. Pressure relief (PR) provided by an APAM is time-varying. A computerized system that measures IP, air pressure, and pressure-time characteristics of dynamic support surfaces has been developed for performance assessment. Using this system, IP was recorded continuously and the durations of pressures below three thresholds (30, 20, and 10 mmHg) were calculated automatically. Fifteen sound volunteers were used to evaluate the pressure-relieving characteristics of four APAMs, including one overlay. Results indicated significant differences (p < 0.001) between products when durations below 20 and 10 mmHg thresholds were analyzed, showing some devices were only capable of momentarily relieving pressure. Maximum contact pressures on the sacrum were significantly lower (p < 0.0001) on devices where inflation pressure was adjusted according to the body mass of the subject. With further clinical validation, this tool could assist in the selection of alternating surfaces of any description.