84
U N I T 1
Cell and Tissue Function
the plasma. Hyperbaric oxygen is currently reserved for
the treatment of problem wounds in which hypoxia and
infection interfere with healing.
Impaired Inflammatory and Immune
Responses
Inflammatory and immune mechanisms function in
wound healing. Inflammation is essential to the first phase
of wound healing, and immune mechanisms prevent
infections that impair wound healing. Among the condi-
tions that impair inflammation and immune function are
disorders of phagocytic function, diabetes mellitus, and
therapeutic administration of corticosteroid drugs.
Phagocytic disorders may be divided into extrinsic
and intrinsic defects. Extrinsic disorders are those that
impair attraction of phagocytic cells to the wound site,
prevent engulfment of bacteria and foreign agents by
the phagocytic cells (i.e., opsonization), or cause sup-
pression of the total number of phagocytic cells (e.g.,
immunosuppressive agents). Intrinsic phagocytic dis-
orders are the result of enzymatic deficiencies in the
metabolic pathway for destroying the ingested bac-
teria by the phagocytic cell. The intrinsic phagocytic
disorders include chronic granulomatous disease, an
X-linked inherited disease in which there is a deficiency
of myeloperoxidase and nicotinamide adenine dinucleo-
tide peroxidase (NADPH)–dependent oxidase enzyme.
Deficiencies of these compounds prevent generation of
hydrogen superoxide and hydrogen peroxide needed for
killing bacteria.
Wound healing is a problem in persons with dia-
betes mellitus, particularly those who have poorly
controlled blood glucose levels.
27
Studies have shown
delayed wound healing, poor collagen formation, and
poor tensile strength in diabetic animals. Of particular
importance is the effect of hyperglycemia on phagocytic
function. Neutrophils, for example, have diminished
chemotactic and phagocytic function, including engulf-
ment and intracellular killing of bacteria, when exposed
to altered glucose levels. Small blood vessel disease is
also common among persons with diabetes, impairing
the delivery of inflammatory cells, oxygen, and nutrients
to the wound site.
The therapeutic administration of corticosteroid
drugs decreases the inflammatory process and may delay
the healing process. These hormones decrease capillary
permeability during the early stages of inflammation,
impair the phagocytic property of the leukocytes, and
inhibit fibroblast proliferation and function.
Infection,Wound Separation, and
Foreign Bodies
Wound contamination, wound separation, and for-
eign bodies delay wound healing. Infection impairs
all dimensions of wound healing.
28
It prolongs the
inflammatory phase, impairs the formation of granu-
lation tissue, and inhibits proliferation of fibroblasts
and deposition of collagen fibers. All wounds are
contaminated at the time of injury. Although body
defenses can handle the invasion of microorganisms at
the time of wounding, badly contaminated wounds can
overwhelm host defenses. Trauma and existing impair-
ment of host defenses also can contribute to the devel-
opment of wound infections.
Approximation of the wound edges (i.e., suturing of
an incision type of wound) greatly enhances healing and
prevents infection. Epithelialization of a wound with
closely approximated edges occurs within 1 to 2 days.
Large, gaping wounds tend to heal more slowly because
it is often impossible to effect wound closure with this
type of wound. Mechanical factors such as increased
local pressure or torsion can cause wounds to pull apart,
or
dehisce
.
Foreign bodies tend to invite bacterial contami-
nation and delay healing. Fragments of wood, steel,
glass, and other compounds may have entered the
wound at the site of injury and can be difficult to
locate when the wound is treated. Sutures are also for-
eign bodies, and although needed for the closure of
surgical wounds, they are an impediment to healing.
This is why sutures are removed as soon as possible
after surgery. Wound infections are of special concern
in persons with implantation of foreign bodies such
as orthopedic devices (e.g., pins, stabilization devices),
cardiac pacemakers, and shunt catheters. These infec-
tions are difficult to treat and may require removal of
the device.
Wound Healing in the Elderly
A number of structural and functional changes have
been reported to occur in aging skin, including a
decrease in dermal thickness, a decline in collagen con-
tent, and a loss of elasticity.
29,30
The observed changes
in skin that occur with aging are complicated by the
effects of sun exposure. Since the effects of sun expo-
sure are cumulative, older persons show more changes
in skin structure.
Wound healing is thought to be progressively
impaired with aging. The elderly have alterations
in wound-healing phases including hemostasis and
inflammation, cell proliferation, and resolution.
30
Keratinocytes, fibroblasts, and vascular endothelial
cells display a reduced rate of proliferation. There is
also a reported decrease in angiogenesis and collagen
synthesis, impaired wound contraction, and slower
reepithelialization of open wounds. Although wound
healing may be delayed, most wounds heal, even in the
debilitated elderly patient undergoing major surgical
procedures.
The elderly are more vulnerable to chronic wounds,
chiefly pressure, diabetic, and ischemic ulcers, than
younger persons, and these wounds heal more slowly.
However, these wounds are more likely due to other dis-
orders such as immobility, diabetes mellitus, or vascular
disease, rather than aging.
