Ambient Pressure Changes as an Unrecognized Risk Factor for Pressure Ulcer Development in Wheelchair Users with Air...

Air cell-based wheelchair seat cushions are widely used for pressure ulcer prevention in individuals with limited mobility. However, the influence of ambient pressure variations on the mechanical surface pressure acting on users has not been systematically investigated. This study presents a dedicated measurement concept to quantify these effects under controlled laboratory conditions. Surface pressure was quantified using a dual-range FSR sensor calibration, achieving a minimum resolution of 0.0012 N/cm² per digit. Five representative scenarios were investigated, covering ambient pressure reductions between 30 hPa (elevator rides) and 250 hPa (aircraft takeoff). Measurements were conducted across 150 series, combining five initial internal cushion pressures and six load levels. Ambient pressure reductions led to measurable increases in surface pressure across all conditions, ranging from 11.2 ± 11.0% (30 hPa) to 62.0 ± 45.3% (250 hPa). Risk assessment based on a pressure-time cell death model revealed risk category changes in up to 66.7% of all conditions. Mean reductions in time to cell death ranged from 16 min (30 hPa) to 55 min (250 hPa), following a logarithmic relationship (adjusted R² = 0.984). These findings highlight ambient pressure variation as a previously unrecognized influencing factor on pressure ulcer risk in wheelchair users with air cell-based seat cushions.