We’re continuing our blog series focused on Understanding Cushion Properties with the Help of ANSI/RESNA and ISO Standards. Today’s blog takes a closer look at the ISO standard 16840-6 of simulation of aging standard and the pressure mapping test method.
Pressure, shear, and microclimate are the key characteristics called out in the clinical practice guideline in the definition of pressure injuries. There are standards that address these factors. The ISO standard 16840-6 is a simulation of aging standard, and it begins by characterizing the cushion. In the chart below you can see a list of all of the different properties that can be measured with the standard. The thought is you can measure these properties, then apply a simulation of aging by exposing the cushion to challenges it would experience during its “useful life”, such as fluids, ozone, soiling, cleansing, disinfection, and so on. You then remeasure the properties and see if anything has changed. This standard is very useful as it has a collection of ways to identify and understand how the cushion performs, new, “out of the box” to help with the process of matching the right solution to the client. The standard further gives an indication of how these properties might change over time: over three years or five years, are you still getting the same type of performance that you got on day one?
Pressure Mapping Test Method
Pressure Mapping is one of the tests applied to characterize the cushion. If you work in wheelchair seating, pressure mapping is a test you’re most familiar with. One of the main goals with wheelchair cushion is to provide pressure redistribution, so pressure mapping is a very common tool in the clinic. There are limitations to pressure mapping systems, and the mat itself interferes with the evaluating how the cushion truly interacts with the seated client. It also, of course, does not give information about how the internal tissues may be affected. Pressure mapping can, however, give some cursory information in the clinic, when different solutions are being considered, as a limited tool in the process of clinical reasoning. However, simply looking at data provided by different manufacturers becomes tricky, as it might not be clear how the cushion was set up when the data was obtained, how the person was set up, what their body types and needs were, and so on. To reduce these sources of variability, pressure mapping becomes a more useful tool when it is in a laboratory setting under an ISO standard.
Bench testing under controlled conditions can start to minimize the variables. A physical form was created that’s shaped like the buttocks and is rigid. Since this “indenter” is rigid, it doesn’t reproduce a human body, but it does give a standardized shape, size, and stiffness that a standardized weight can be applied to, as part of the full scientific testing protocol. This means the tests are repeatable, and data can be compared if you want to evaluate the effect of changing cushions or covers, or if a cushion designer wants to evaluate different materials and constructions to see what the effects are and whether or not performance may be improved. This standardization gives you an apples to apples comparison. When you have controlled the variables, you get a clearer view of what may be different across different technologies and different cushion solutions. Again, the ISO standard methods don’t indicate pass or fail, but the test results can help narrow choices you might want to consider for your client.
Let’s look at some data from the University of Pittsburgh obtained using the ISO standard 16840-6 method for pressure mapping under those controlled conditions in their Tissue Integrity Management Laboratory. In this case, a very general takeaway is that even though these are many cushions classified or promoted as “skin protection cushions” they demonstrate different contact areas, different peak and average pressures. The maps provide insightful data for the clinical decision-making process.
Join us next week as we continue looking at the different test methods within the ISO 16840-2 standard and focus on the immersion test method.
Images provided by the University of Pittsburgh Tissue Integrity Management Laboratory
Kara Kopplin, B.Sc.Eng,
Chair of the ANSI/RESNA Wheelchair and Related Seating Committee, Director of Regulatory Science for Permobil
Kara Kopplin holds a B.Sc. in Ceramic Engineering from the University of Missouri-Rolla, U.S.A., bringing a unique and complementary materials engineering perspective to seating solutions. In her role as Director of Regulatory Science for Permobil, Inc., Ms. Kopplin actively contributes to the efforts of the International Organization for Standardization (ISO) and European Committee for Standardization (CEN) to develop object test methods for wheelchair systems and components. She is honored to chair the ANSI/RESNA Standards Committee on Wheelchair and Related Seating (WRS) in the US and encourages everyone to contribute to the development of these critical evaluation tools.