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.

Inclusion Criteria:

- have had spinal cord injury for more than one year

- have injury level at T10 or above

- not ambulatory and use a wheelchair for mobility

- none smokers or able to refrain from smoking four hours prior to and during the study

Exclusion Criteria:

- current pressure ulcer

- history of diabetes mellitus

- history of cardiovascular diseases

- history of hypertension

- history of pulmonary diseases

- pregnant women (based on a positive pregnancy test)

- Non-English speakers