Alternating Pressure Overlay on Weight Bearing Tissue Tolerance in People With Spinal Cord Injury

Tissue ischemia is one of the main etiologies of pressure injury. It is inevitable during bed-ridden and wheelchair bound conditions, such as spinal cord injury (SCI), or prolonged surgery procedure in the operating room. Active alternating pressure (AP) mattresses are covered by Medicare policy for patients with multiple/large stage 2/ stage 3 pressure injuries to relief interface pressure and prevent recurrence of pressure injuries. Previous studies demonstrated that the protective mechanisms of AP on pressure injury include redistribution of surface pressure, and allowing more blood supplies while lying on the support surface. The Dabir AP overlay is low profile yet possesses similar characteristics as other AP mattresses on the market; it is intended for clinical use, such as operation room (OR) where AP mattresses may not be an option. We expect Dabir AP overlay will be beneficial to people at risk of pressure injury by maintaining the blood supply during weight bearing condition.

The objective of this study is to evaluate the protective mechanisms of Dabir AP overlay on weight bearing tissue of people with chronic spinal cord injury (SCI). Our central hypothesis is that the Dabir AP overlay will cause lower amount of interface pressure and allow more skin blood flow during weight bearing as compared to regular OR overlay.

Each subject will undergo two study protocols: AP and control, and the order of the protocols will be randomized by drawing one envelope from the envelope pool. We will start with a pool of total 20 envelopes (10 envelopes indicating AP protocol first, and 10 envelopes indicating control protocol first). A 30-minute washout period will be provided in between the two protocols. Two Laser Doppler flowmetry (LDF) flat probes (moor instrument, Wilmington, DE) will be taped to the sacrum and one heel to collect the skin blood flow response throughout both AP and control protocols. A whole body pressure mapping system will be used between the subject and the overlay to collect the inter pressure data. For the AP cycle, we will use four 10-minute cycles (5 minutes of high pressure and 5 minutes of low pressure).

AP protocol: The subject will first lie on his/her side quietly for 10 minutes to collect the baseline skin blood flow, followed by lying supine on the Dabir AP overlay for 40 minutes, and then side lying for 30 minutes to collect the first reactive hyperemic response. To test the effect of preconditioning, the subject will then lie supine on the OR overlay for 40 minutes followed by side lying for 30 minutes for the second reactive hyperemic response.

Control protocol: The subject will first lie on his/her side quietly for 10 minutes to collect the baseline skin blood flow, followed by lying supine on the OR overlay for 40 minutes, and then side lying for 30 minutes to collect the reactive hyperemic response for control protocol.

The PI, or key personnel will then collect the vascular control measures, including the heat hyperemic (HH) blood flow response, and the skin vasomotor response. A non-invasive combined laser Doppler and white light reflectance spectroscopy (LDF-WLRS) probe (CP2T-1000, Moor Instrument, Wilmington, DE) will be used for both measures.

HH blood flow response will be measured at the sacrum and one heel while the subject is in side-lying position. HH will be induced with the heater at the tip of the probe head (41°C for 5 minutes). This HH measure will take approximately 7 minutes (2 min-baseline, 5 min-heating) per location. In total, the HH measures will take up to 15 minutes to complete.

The skin vasomotor response will be induced using cutaneous electrical stimulation (3-10 mA, 0.2-1.0 ms pulses at 20 Hz, 1 s trains) delivered via 1 cm Ag-AgCl surface electrodes applied bilaterally (4 cm apart) to the forehead (above lesion) and the abdominal wall (below lesion) while the subject is in a semi-reclined position.12 For each site, 5-8 stimuli will be delivered randomly. CP2T-1000 probe will be used to collect SBF and tissue oxygenation data at pulp of the second finger and toe. Subject will be in a semi-reclined position (about 30° from horizontal plane) during this protocol, and it will take up to 15 minutes to complete this protocol.

Pressure mapping of wheelchair: (approximately 10 minutes) The subject will be asked to transfer back to his/her wheelchair with the pressure mapping system placed between the wheelchair and the subject to collect the interface pressure data. The pressure mapping system is the same as that used between the subject and overlay to collect the interface pressure data.