Effectiveness of alternating pressure overlay on skin blood flow and interface pressure in people with spinal cord injury.

Purpose: To test the protective mechanisms of alternating pressure (AP) overlay on weight-bearing soft tissues (i.e. sacrum and heel) in people with chronic spinal cord injury (SCI).

Hypothesis: The AP overlay will reduce the interface pressure and allow more skin blood flow (SBF) at sacrum and heel as compared to the regular operating room (OR) overlay.

Methods: Fifteen adults (age 41.87±14.89 years old) with SCI were recruited (4 female, 11 male). They have injury level at T10 and above, AIS A, B or C for more than one year. This study is a repeated measures design. All the subjects underwent two protocols (30 minutes each): lying supine on OR overlay, and lying supine on OR overlay with AP in between. Interface pressure and SBF were collected at sacrum and left heel using the pressure mapping system and laser Doppler flowmetry respectively. Friedman tests were used to compare the difference in interface pressure, SBF among OR only, AP during inflation (AP-inflat), AP during deflation (AP-deflat) at the sacrum and heel. Wilcoxon signed rank tests were computed for pair-wise comparison (p<0.016 as significant after Bonferroni correction).

Results: Interface pressure at sacrum, and heel was significantly lower with AP-deflat (sacrum:51.47 mmHg, heel:26.79 mmHg) as compared to AP-infalt (sacrum:89.27 mmHg, heel:52.49 mmHg) and OR (sacrum:114.13 mmHg, heel:53.49 mmHg). Sacral SBF was significantly higher with AP-deflat (15.60 au) as compared to AP-inflat (12.54 au), whereas heel SBF was only significantly higher with AP-deflat (26.47 au) as compared to OR (12.06 au). The effect size of sacral SBF between AP-deflat and OR (3.54 au), and heel SBF between AP-deflat vs. AP-inflat (11.47 au) is large, indicating clinical significance.

Conclusion: Alternating pressure overlay is beneficial to SCI patients by redistribuing interface pressure and increasing SBF at weight-bearing areas.