Lateral Pressure Application to the Seated Buttocks Largely Maintains Transcutaneous Gas Tensions at the Ischial...

This study aimed to evaluate the physiological effectiveness of lateral pressure application in maintaining baseline transcutaneous oxygen (TcPO₂) and carbon dioxide (TcPCO₂) tensions in the buttocks during sitting, compared with a conventional static foam cushion. Secondary aims were to determine whether body mass index (BMI) influenced the physiological response when lateral pressure was applied and to investigate the relationship between transcutaneous oximetry and underbody interface pressure. A prospective, controlled, repeated-measures laboratory study was conducted with 30 healthy adults. Participants underwent two 20-min sitting conditions: sitting on static foam alone and sitting on static foam with lateral pressure applied by a prototype device. Transcutaneous gas tensions were measured at the right ischial tuberosity using an oximeter and normalised to unloaded standing baselines. Tissue responses were categorised according to the Chai and Bader tissue-response criteria, where changes in gas tensions of < 25% are Category 1, least risk, and changes of > 25% are Category 3, highest risk. Underbody interface pressures were recorded using a pressure-mapping array. Statistical comparisons between conditions were performed using paired parametric or non-parametric tests as appropriate. Mean and peak underbody interface pressures were significantly reduced (p < 0.0001) when lateral pressure was applied. Lateral pressure significantly reduced the mean change in TcPCO₂ compared to static foam alone (11.9% ± 25.6% and 47.8% ± 72.9%, respectively, p < 0.0001) and reduced the change in TcPO₂ to -29.5% ± 23.5% compared to -50.4% ± 34.8% with static foam alone (p < 0.0001). Eleven participants exhibited a Category 3 ischaemic response on static foam, compared with only two when lateral pressure was applied. Twenty-nine of 30 participants moved to a more favourable or unchanged tissue-response category when lateral pressure was applied. No correlation was found between interface pressure and changes in gas tensions. No significant differences were observed between BMI groups. Application of lateral pressure during sitting maintained tissue perfusion at the ischial tuberosity more effectively than static foam alone. These findings support the physiological rationale for applying lateral pressure as a novel strategy for pressure-ulcer prevention in seated patients.