Wound Formation, Treatment, and Healing
The occurrence of pressure ulcers among the elderly and in hospitalized
patients has an extensive impact on patients and health care providers
in terms of decreased quality of life, loss of productivity, and
high cost of treatment. Various studies indicate that 50-60% of
all pressure ulcers in acute hospital populations develop after
admission and thus are deemed preventable (i.e., more frequent risk
assessment, treatment plans, specialty devices, etc.). Although
extensive literature exists concerning pressure ulcers, there remains
no clear consensus regarding the etiology of such wounds. Rather,
several factors are known to contribute to the formation and persistence
of pressure-related wounds (i.e., elevated pressure over extended
time, shear, elevated pressure augmented by elevated temperature,
age, poor nutrition, incontinence, fractures, paralysis or lack
of sensation, arterial insufficiency, venous stasis, diabetes).
Specifically, there are few detailed reports about the thresholds
of wound formation with respect to pressure, temperature, and duration
of application, and lack of clear consensus about the proper form
of treatment. Clinicians use a variety of visual methods to evaluate
the status of skin tissue, however these methods lack precision,
and quantification of slow or subtle changes may be difficult. Accurate
determination of the extent and depth of subsurface injuries would
allow for appropriate and timely therapeutic intervention.
Related studies in our lab include the following:
- Development of a porcine model to facilitate investigation
of pressure ulcer formation, healing, and prevention (Figures 1
and 2). This model allows for easy, independent modulation of pressure,
temperature, and duration parameters to create specific classes
of wounds [1].
- Investigation of the effects of duration of applied pressure
and applied temperature on wound formation, as well as the threshold
temperature below which focalized cooling will minimize the potential
for wound formation using a porcine model. The benefits of focal
cooling were evident at an extended duration and at deep tissue
layers, and suggest future clinical applications for pressure ulcer
prevention and therapy [2].
- Examination of the use of cutaneous reactive hyperemia
as a means for noninvasive assessment of wound severity of newly
formed temperature-modulated pressure injuries in a porcine model.
This study employed color image analysis to determine the severity
of wounds and infrared imaging/computer image processing to detect
differences in skin temperature. Both techniques correlated with
the severity of injuries as determined by a histologic assessment
of biopsied tissue, however infrared imaging provided the better
means to assess wound depth [3].
- Critical assessment of potential methodologies for noninvasive
wound evaluation using a color imaging system, development of a
method for quantifying histological readings, and testing these
techniques on a porcine model of wound formation. Color analyses
enabled statistically significant differentiation of mild, moderate,
and severe injuries within 30 minutes after application of the injury,
and again when the wounds were 5-7 days old; this technique could
be adapted for assessing and tracking wound severity in humans in
a clinical setting [4].
- Explicit definition of critical thresholds of applied pressure,
duration, and temperature in the formation of pressure ulcers or
cutaneous burns in a porcine model. Pathological changes in pressure
ulcers were found to begin at the deep muscle and progress upward
into the cutaneous layers with increasing pressure and/or duration
of contact; muscle degeneration was also observed after 5 hours
of ischemia (Figure 3). Thresholds for all four cutaneous layers
increased with a decrease in applied temperature, suggesting that
these deep tissue changes could be lessened or prevented with appropriate
focal cooling. Such predictions of thresholds for injury causation
could provide a predictive basis for the design and development
of support surfaces and patient turning schedules for the prevention
of tissue injury [5].
- Noninvasive assessment of the severity and depth of pressure
injuries in dermal and subdermal tissue using infrared thermography
in a porcine model. Two techniques were investigated: 1) thermographic
evaluation of wounds at thermal equilibrium with normal room temperature
surroundings, and 2) observation of temperature changes that occurred
to the wound area after application of focal cooling. Deep tissue
injuries were easily distinguished from shallow wounds by their
thermal response to focal cooling, suggesting clinical utility for
detecting abscessed areas of skeletal muscle that are concealed
by a healthy epidermal or dermal bridge (6).
Figure 1. Cluster of 4 discs was designed to apply pressure
to preselected wound sites. Temperature
modulation was facilitated with a micro-processor-controlled unit;
cooling was provided by a water
bath and heating by electrical resistance wire. Temperatures were
maintained within ±0.5°C.
Figure 2. Disc application and subsequent assessment
sites
Figure 3. Illustrative representation of tissue
damage at combinations of pressure,
temperature, and duration that resulted in tissue alterations
References:
- Kokate JY, Leland KJ, Held AM, Hansen GL, Kveen GL, Johnson BA,
Wilke MS, Sparrow EM, Iaizzo PA: Temperature-modulated pressure
ulcers: a porcine model. Archives of Physical Medicine and Rehabilitation
76: 666-673, 1995.
- Iaizzo PA, Kveen GL, Kokate JY, Leland KJ, Hansen GL, Sparrow
EM: Prevention of pressure ulcers by focal cooling: histological
assessment in a porcine model. Wounds: A Compendium of Clinical
Research and Practice 7: 161-169, 1995.
- Hansen GL, Sparrow EM, Kammamuri R, Iaizzo PA: Assessing wound
severity using color and infrared imaging of reactive hyperemia.
Wound Repair and Regeneration 4: 386-392, 1996.
- Hansen GL, Sparrow EM, Kokate JY, Leland KJ, Iaizzo PA: Wound
status evaluation using color image processing. IEEE Transactions
on Medical Imaging 16: 78-86, 1997.
- Kokate JY, Leland KJ, Sparrow EM, Iaizzo PA: Critical thresholds
for pressure ulcer formation in a porcine model. Wounds: A Compendium
of Clinical Research and Practice 9: 111-121, 1997.
- Hansen GL, Sparrow EM, Kalieta AL, Iaizzo PA: Using infrared
imaging to assess the severity of pressure ulcers. Wounds: A Compendium
of Clinical Research and Practice 10: 43-53, 1998.
Patents Related to this Research:
- US5837002: Support apparatus with localized cooling of high-contact-pressure
body surface areas. Augustine SD, Iaizzo PA, Sparrow EM, Johnson
PS, Arnold RC, Stapf DE: Issued November 17, 1998.
- US6010528: Support apparatus which cradles a body portion
for application of localized cooling to high-contact-pressure body
surface areas: Augustine SD, Iaizzo PA, Sparrow EM, Johnson PS,
Arnold RC; Issued January 4, 2000.
- US6123716: Support apparatus which cradles a body portion
for application of localized cooling to high contact-pressure body
surface areas. Augustine SD, Iaizzo PA, Sparrow EM, Johnson PS,
Arnold RC: Issued September 26, 2000.
- US6224623: Support apparatus which cradles a body portion
for application of localized cooling to high contact-pressure body
surface areas.. Augustine SD, Iaizzo PA, Sparrow EM, Johnson PS,
Arnold RC: Issued May 1, 2001.
- US6497720: Support apparatus with a plurality of thermal
zones providing localized cooling. Augustine SD, Iaizzo PA, Sparrow
EM, Johnson PS, Arnold RC: Issued December 24, 2002.
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