Wounds heal quickly. Certain wounds are more susceptible than others to non healing. When bacteria can infiltrate a wound, such as in battle conditions or in older patients, the bacteria damage tissue and inhibit healing. In diabetic patients poor circulation and a large increase in tissue necrotic factor alpha and interleukin 2 prevent wounds from healing. Diabetic foot ulcers can result in amputation of limbs and many times are followed by death. About 70,000 amputations per year are linked to diabetic foot ulcers.
Pressure sores, also called decubitus ulcers, are injuries to the skin and underlying tissues caused by direct pressure over time to superficial tissues, including weight bearing over bony prominence, and shearing force on the skin. They can be exacerbated by excessive moisture on the skin, occlusion of lymphatic vessels, stress and smoking.
Pressure sores range from a very mild pink coloration of the skin, which disappears in a few hours, to a very deep wound extending through bone or into internal organs. These sores are classified in stages according to the severity of the wound. The most common scale to assess pressure sores is the National Pressure Ulcer Advisory Panel Scale which grades sores by 4 grades. Stage 1 is a non-blanchable erythema of intact skin. Stage II is partial loss of skin thickness where the ulcer presents as a skin abrasion. Stage III involves full loss of skin and necrosis to underlying fascia. Stage IV involves skin and fascia and or bone and muscle necrosis.
Pressure sores are a common medical problem causing substantial morbidity. For example, the incidence of pressure sores during hospitalization from stroke is 21%. The incidence of pressure sores is over 30% per year in patients with spinal cord injuries, and after hospitalization from stroke. The incidence of pressure sores is 41% in elderly patients discharged from a nursing home without stroke. In these cases, poor nutrition, moisture on the skin and heavy pressure on areas of the body from lying in bed causes the skin to break down. Even pregnant women in hospitals are susceptible to pressure sores.
Once pressure sores develop, they can take months to heal, or can remain chronically open sores. They often become infected leading to local abscess and septicemia, and have an average cost of medical care of $26,000 per wound.
Treatment of pressure sores include removal of the cause, the application of topical substances, debridement, and surgical procedures where the wounds are covered with tissue flaps. However, these treatments are often unsuccessful and, even when successful, are associated with a high recurrence rate.
Other types of soft tissue wounds may include, but not be limited to, diabetic ulcers, burns, and surgical incisions. Diabetic ulcers cause over 70,000 amputations a year in the United States alone. A method and system for treating such pressure sores and other soft tissue wounds would be desirable.
An estimated 16 million Americans are known to have diabetes, and millions more are considered to be at risk for developing the disease. Diabetic foot lesions are responsible for more hospitalizations than any other complication of diabetes. Among patients with diabetes, 15% develop a foot ulcer, and 12–24% of individuals with a foot ulcer require amputation. Indeed, diabetes is the leading cause of nontraumatic lower extremity amputations in the United States.
It is known to use electrical stimulation to promote healing of soft tissue wounds. Previous studies of electrical stimulation to treat pressure sores employed electrical stimulation with variation of stimulation parameters, such as current and waveform. Almost all modes of stimulation healed sores to some extent, but no studies optimized stimulation parameters. Additionally, the electrode placement and cross sectional area of the electrodes varied, the extent of the sores (stages I–IV) varied, as did the length of time the areas were stimulated.
The direction of the current (positive or negative) and the intensity of the current that optimizes wound healing varies in different phases of wound healing. A substantial body of research show that, while the direction or amplitude of current applied to a wound seems to always help healing, at certain phases of the process some currents work better. However, there has been little objective measure of the phases of wound healing in relationship to when to apply various currents and waveforms that enable optimizing healing for different types of wounds. It is generally known, for example, that in the initial few days after a wound injury, during the first inflammatory phase, skin generates a positive voltage potential. This positive potential, if enhanced, causes increased migration of white cells and increased clotting to the area in and around the wound. In contrast, after the first few days, to dissolve the clot and increase macrophage (white cell) or endothelial cells migration to the wound negative potentials are needed. But the amplitude of these potentials does not appear to be constant in different phases of wound healing. Further, little has been done to characterize the polarity and currents required for healing diabetic ulcers versus pressure sores, versus conventional wounds. Therefore, a great deal remains unknown in terms of when to apply a certain type of current and at what intensity to optimize healing.
For example, with reference to FIG. 1, one prior art system uses two electrodes 10 disposed closely adjacent to and on opposite sides of a wound 12 so that the path of current is across the wound. Modified square wave DC biphasic pulses are used, up to 100 pulses per second. Since the electrodes are placed across the wound, however, the electrical stimulation travels in a path of lowest resistance and the pattern of current flows between the two electrodes resemble that of Maxwell field lines as shown in FIG. 1, with the highest intensity through the center and intensity reduced exponentially, the further away the tissue is from the shortest line connecting the two electrodes. Therefore, for wounds that are irregularly shaped, or wounds that are deep such as stage 4 pressure sores, very little current actually travels into the wound, and electrical stimulation of such pressure sores results in low rates of healing. One reason diabetic ulcers don't seem to heal is that the epithelial layer builds on the edge of the wound, but growth factors are absent to cause migration to the center of the wound. With electrical stimulation, for whatever cause, the cells migrate.
What is known is that one of the most important processes in wound healing is re-epitheliazation. Studies using animals and man show that on the outside area of a wound, a strip of intact skin approximately 0.5 mm wide surrounds the wound. It is in this area that substantial voltage gradients occur. The mechanism by which cells migrate is poorly understood; however, the voltages generated by a typical wound, which can range as high as 120 mV/mm, are quite sufficient to cause cell migration and wound healing. For example, in one study on guinea pigs, it was shown that voltage gradients as low as 7 mV/mm caused substantial healing around wounds. A summary of the effect of currents on wounds is given below. Generally, negative currents (1) decrease edema around the electrode, (2) lyase or liquefy necrotic tissue, (3) stimulate growth of granulazation tissue, (4) increase blood flow, (5) cause fibroblasts to proliferate and make collagen, (6) induce epithelial cell margins to move, (7) attract neutrophils, and (8) stimulates neurite growth directionality. In contrast, positive currents (1) promote epithelial growth and organization, (2) act as vasoconstrictors and induce clumping, (3) denature protein, (4) aid in preventing post ischemic lipid peroxidation, (5) decrease mass cells in healing wounds, and (6) attract macrophages. Obviously different currents at different points in wound healing would be beneficial. However, up to this point no known device has been able to detect the optimal current to apply into each area of the wound. This is complicated further by the fact that wounds don't heal uniformly. One area of the wound may heal quite quickly while another area does not. This is common in pressure sores and diabetic ulcers. Generally, more superficial area of the wound heals very quickly whereas a deeper area of the wound may take months to heal but even in superficial wounds, one margin may heal more quickly than others due to drying or escar formation blocking healing. In this respect then, applying a positive current for a long period of time may be good for one part of the wound, but may be very poor for another portion of the wound, and may in fact inhibit healing. It is not surprising, then, that wounds seem to heal quickly with either positive current, negative current or alternating current. However, no one study has tried to divide the wound into healing sectors and optimize healing by varying the currents in different areas of a wound.
For these reasons among others, while therapists use electrical stimulation to treat pressure sores, there is no FDA approval of electrical stimulation for treatment of pressure sores or other soft tissue wounds. Further, conventional systems are expensive and complex. Therefore, it would be useful to have a system for the application of electrical stimulation to pressure sores that optimizes stimulation parameters. Further, it would be useful to have a system that a patient could use at home to apply electrical stimulation to a pressure sore. Still further, it would be useful to have a system that applied different currents at different points in wound healing, and which is able to detect the optimal current to apply into each area of the wound, and which divided the wound into healing sectors and optimized healing by varying the currents in different areas of a wound.