WO1997001372A1

WO1997001372A1 - Apparatus and method for healing wounds using electrical stimulation

Info

Publication number: WO1997001372A1
Application number: PCT/US1996/011093
Authority: WO
Inventors: Dean L. Kellogg, Jr.
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 1995-06-29
Filing date: 1996-06-28
Publication date: 1997-01-16
Also published as: AU6481496A

Abstract

An apparatus (40) and method for treating wounds with AC electrical stimulation is disclosed. The method consists of placing an electrode (20, 30) directly into the wound, placing the other electrode either into or outside the wound in close proximity to the first electrode, and applying AC current to the electrodes providing a current density of about 0.075 mA/cm2 to 0.150 mA/cm2 at a frequency of about 0.0027 Hz to 10 Hz.

Description

DESCRIPTION

APPARATUS AND METHOD FOR HEALING

WOUNDS USING ELECTRICAL STIMULATION

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a method and apparatus for treating soft tissue wounds. More particularly, it relates to a method and apparatus for accelerating the healing of chronic wounds by electrical stimulation.

Prior Art

It is well known that changing the electrical and/or electrical chemical environment of living tissues causes a modification of the growth, repair, and maintenance behavior of the tissue. Modification is carried out by subjecting tissue to electrical current. This use of directly applying electrical current to augment the healing of soft tissue wounds and incisions as well as bones has been proposed for many years. Maurer, U.S. Patent No. 4,556,051; Stephen U.S. Patent No. 5,344,440.

Prior attempts at applying electrical treatments to the human body generally used direct current. This was found to be accompanied by a number of undesirable side effects, such as the occurrence of skin injury in the form of iontophoretic burns and irritation in the treated area, as well as the formation of undesirable vesicles or bulla, on the skin and in the treated area. Various complicated or compromised methods for preventing these iontophoretic burns have been developed. However, such methods and apparatus have generally been found not to be adequately effective for preventing irritation in the formation of vesicles or bulla on the skin and treated area. Consequently, iontophoretic treatments have usually been limited to relatively low electrical currents and relatively short periods of administration of, typically, twenty minutes or less.

An innovative method for avoiding skin injury during iontophoresis was recognized by Tapper, U.S. Patent No. 5,224,927 which uses an alternating current rather than the traditional direct current. However, the Tapper patent focuses on a method of drug delivery through iontophoresis, rather than a method of healing wounds. The LectroPatch™ is a commercial embodiment of the Tapper patent and is currently used to deliver drugs through the skin by means of iontophoresis.

The unique AC current system of the LectroPatch™ iontophoresis system is an important safety feature that allows direct application of the device to heal wounds. Standard iontophoresis systems employ continuous direct current which makes them unsuitable for wound healing applications because of two significant limiting factors. First, DC iontophoresis is thought to cause polarization in the skin orientating the skin in a direction opposite that of the applied field. The skin then acts like a capacitor decreasing the effective current passing through the skin as the duration of DC current continues. In an effort to avoid this polarization pulsed DC iontophoresis has been used with limited success. McWhorter, et al. , U.S. Patent No. 5,158,081. It has been found that the slow AC cycle of the LectroPatch™ system overcomes this problem of skin polarization.

The second and more serious limiting factor in the efficacy of both continuous and pulsed DC systems is the generation of electrochemical burns.

With both types of DC iontophoresis, H+ ions accumulate at the anode and OH- ions at the cathode, leading to pH changes at both sites. These changes cause tissue damage via electrochemical burns. The risk of electrochemical burns due to the pH changes increases with prolonged current application and high current densities. This problem has limited DC iontophoresis to periods of fifteen minutes or less and to current densities of lmA/cm² or less. These limitations reduce the effectiveness of iontophoresis or wound healing using DC currents. It has been found that electrochemical burns can be avoided by using AC current during the iontophoresis process. This neutralizes the ions that have been building up. Alternating current iontophoresis generates H-l- ions during first phase and OH- ions during the second phase when it reverses polarity, thus neutralizing the pH changes taking place in the wound at the electrode sites and avoiding electrochemical burns.

Applicant recognizes Bach et al. , The Effect of Electrical Current on Healing Skin Incisions, Env. J. Surg. vol. 157, on 171-74 (1991), to be the most relevant prior art. The Bach reference makes use of DC current to enhance the healing of surgical incisions. Surgical incisions normally heal without any serious intervention. Chronic wounds, on the other hand, by definition do not heal without medical intervention.

Chronic, non-healing cutaneous ulcers (hereinafter referred to as "ulcers") are a major unresolved health problem. Typically, cutaneous ulcers appear on an extremity, and are often indicative of a secondary disorder, i.e. a peripheral circulatory disorder. Cutaneous ulcers which are secondary to a peripheral circulatory disorder are generally classified as venous stasis ulcers, diabetic ulcers, or decubitus ulcers. Although most ulcers are secondary to a peripheral vascular disease, some are secondary to dermatological, endocrine, hematological, or other systemic diseases.

Venous stasis ulcers are caused by chronic venous insufficiency. Chronic venous insufficiency is a pathological condition of the skin and subcutaneous tissues of the lower extremity that results from prolonged stasis of the venous blood flow. Venous stasis is primarily caused by an abnormal venous hypertension that exists with post phlebitic conditions or with incompetent varicose veins. The elevated venous pressure disrupts the delicate balance between the intravascular and interstitial forces of the capillary bed. Fluid leaves the intravascular compartment and enters the surrounding interstitial tissue. Edema and stasis develop as a result in most instances. The first observable manifestation of chronic venous insufficiency is usually edema. When the edema has been present for some time, areas of pigment, purpura and petechiae may appear. The longer the edema has been present, the greater the damage, and the greater the tendency for subcutaneous fibrosis to develop, producing areas of induration.

Ulceration is a common disabling complication of chronic venous insufficiency. In many instances, the ulcers develop at the site of minor contusions. In other instances, they develop at areas of dermatitis or chronic induration. Sometimes they follow minor infections in the skin. The ulcers occasionally heal readily, but more often they are chronic, refractory to therapy, and are classified as "non-healing."

Venous stasis ulcers are treated with bed rest and elevation of the legs above the heart level. Pressure is applied to the area of the ulcer, typically by support stockings, to alleviate non-healing in the extremity. Antibiotics are occasionally indicated, especially when the ulcer is surrounded by severe, acute cellulitis. If the ulcer fails to heal spontaneously with these measures, skin grafting may be required. In 1979, there were about 128,000 patients hospitalized primarily for non-healing venous stasis ulcers with an average 11.4 day length of stay, which, at $200 per day, amounted to about $300 million in health care costs.

In contrast to venous stasis ulcers, where there is blood pooling, decubitus ulcers are caused by the ischemic necrosis and ulceration of tissues overlying a bony prominence wliich has been subject to prolonged pressure. Generally, this pressure is caused by a bed, wheelchair, cast, or splint. Decubitus ulcers are most frequently seen in patients who are debilitated, paralyzed, or otherwise long bedridden. Depending on the patient's position various areas on the patient's body may be affected. However, the feet and sacral areas are most often afflicted. Decubitus ulcers can affect not only superficial tissues, but also muscle and bone. The most important single precipitating factor for decubitus ulcers is pressure. The pressure impairs local circulation and causes local tissue anoxia that progresses to necrosis of the skin and subcutaneous tissues. Therefore, decubitus ulcers are treated by alleviating the pressure on the afflicted area, and if possible, by lowering the extremity below the heart level to increase circulation to the area. Decubitus ulcers occasionally heal spontaneously; however, decubitus ulcers are more often refractory to therapy and require surgical intervention.

The clinical syndrome of diabetes mellitus involves large vessel disease, micro vascular disease, and neuropathy. Diabetics have an abnormality of the capillary basal lamina (basement membrane) characterized by thickening of the lamina of capillary beds of the skin and skeletal muscle. The process affects, among other areas, the legs and feet. Microvascular disease, typically in combination with neuropathy, causes the associated skin and underlying tissue to become anoxic. If the tissue remains anoxic for a sufficient time, the tissue becomes necrotic and cutaneous ulcerations form. Generally, these ulcers occur on the feet or lower extremities. The goal of treatment is often returning circulation to the necrotic area. However, because these ulcers are often refractory to treatment, surgical intervention is frequently required.

Why some cutaneous ulcers heal, while others are chronic and refractory to treatment, is not entirely understood. Climcally, ulcers are characterized as non- healing if they are refractory to therapy and are present for greater than a year, or are progressing towards healing at a rate of less than or equal to 1 millimeter per week.

Currently, 50-70% of all amputations not necessitated by trauma are performed in diabetics. 30,000-50,000 amputations are performed in diabetics each year with the mortality rate of up to 7% and a major complication rate of 36%. The cost of amputations alone is $1.3 billion. The need for post- amputation rehabilitation, chronic care, and even nursing home placement, multiply that cost many times. The cost of the patient's loss of independence and quality of life is greater still.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for treating wounds by electrical stimulation while mi iimizing skin injury. The apparatus consists of two electrodes one of which is placed inside of the wound and an AC power source connected to the electrodes delivering about 0.075 to 0.150 mA/cm² at a frequency between about 0.0027 and 10 Hz. The two electrodes are separable which allows large and deep wounds to be treated and avoids electrical short circuits which may occur in treating large wounds. No drug delivery is involved; only AC electrical current is needed to promote the healing of the wounds.

In the present invention, wound healing is enhanced by placing an electrode inside the wound, placing another electrode near the first electrode either inside or outside the wound, and applying AC current to the electrodes at a frequency approximately between 0.0027 and 10 Hz and a current density approximately between 0.075 and 0J50 mA/cm². In a preferred embodiment, the electrodes should be placed least 0J inches, but not more than 2 inches apart from one another.

Stated differently, the healing of a wound on a biological subject may be accelerated by conducting an electric current through a surface of the wound in a first direction from a first electrode to a second electrode on the subject. And intermittently reversing, at a relatively low frequency which prevents skin damage, between approximately 20 times per second and approximately once every three minutes, the polarity of the electrodes to cause electrical current to flow in a second direction opposite to the first direction, whereby such electric treatment of the wound may be continuous for extended periods of time. BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be further illustrated by reference to the appended drawings which illustrate particular embodiments of the electrical stimulation device to heal wounds in accordance with the present invention.

FIG. 1 is a schematic view of a wound being treated with an electrical stimulation device in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be understood that the present invention can be implemented in a number of different ways, all within the spirit and scope of the claims appended hereto. The presently preferred embodiment of the invention will now be described.

Referring first to FIG. 1 a wound 10 is being treated by placing a first electrode 20 into the wound, placing another electrode 30 proximate to and apart from the first electrode 20, and applying to the electrodes alternating current from an AC power source 40. The second electrode 30 is placed proximate to the first electrode 20 such that the electric current passes through and/or around the wound 10, but not so close to the first electrode as to cause a short circuit. It has been found that a space of approximately 1/4" between the two electrodes is sufficient for most applications. For large wounds, the second electrode 30 may be placed inside the wound opposite the first electrode 20. In smaller wounds, it may be necessary to place the second electrode 30 outside and near the periphery of the wound 10.

The AC power source delivers a current density about 0.075 to 0.150 mA/cm² at a frequency about 0.0027 to 10 Hz. It should be noted that no drug delivery is needed; only AC electrical current is necessary to promote the healing of the wound 10 in accordance with the present invention. The first and second electrodes, 20 and 30, may be constructed from any electrically conductive material which is biologically inert such as silicone/carbon, platinum, rhodium, or palladium. The relatively less expensive silicone/carbon electrodes are preferred.

It is also possible to treat two wounds simultaneously by placing an electrode into each wound. Similarly, multiple wounds may be treated simultaneously using pairs of electrodes. Since the stratum corneum, the keratinized layer of the skin, provides most of the electrical resistance in the skin and this layer is absent in a wound, it follows that the path of least resistance will be through the wound and not the surrounding skin. However, if both of the electrodes are placed outside of the wound, a circuit may be established that does not pass through the wound. Thus, it is important that at least one electrode be placed inside the wound. Electrode size may vary according to wound size, e.g. may be larger for larger wounds.

The present invention is disclosed in connection with specific embodiments. However, it will be apparent to one skilled in the art that variations from the illustrated embodiments may be undertaken without departing from the spirit and scope of the invention. Such variations will be apparent to those skilled in the art in view of the above disclosure and are within the spirit and scope of the invention.

Example 1 On October 21, 1993 a diabetic patient having a chronic ulcer with osteomyelitis was treated with an embodiment of the present invention. The ulcer has failed to respond to all known therapies including hyperbaric oxygen. The patient was advised by surgeons that he needed at least a partial foot amputation for the ulcer. Two LectroPatch™ drug delivery systems were used, each being slightly altered. The LectroPatch™ devices were altered such each device functioned as a separate electrode with the two devices being wired together to form an electrode pair between which alternating current could be passed. This allowed the electrodes to be spatially separated. The devices were not loaded with any drug; instead they were was filled with sterile water. One device was placed inside the chronic wound and the other was placed in contact with the skin outside the wound. The device was operated at a frequency of 0.0167 Hz and a current density of 0J50 mA/cm².

The chronic ulcer began healing within a few weeks and healed completely after seven months of daily 30 minute treatments. No drug delivery was involved only AC electrical current was used.

Example 2

Two patients with grade 3-4 diabetic leg ulcers with osteomyelitis failed to respond to the usual therapies. One of these patients was advised by surgeons that he needed at least partial foot amputations for the ulcers. The patient had a prior below the knee amputations of one leg because of diabetic leg ulcers. The second patient had several large ulcers on both feet and had therapeutic fly maggots removed from the wounds the day prior to initiation electrical stimulation. Both patients elected to have daily thirty minute treatments using the modified LectroPatch™ in accordance with the present invention. In two weeks of initiating these treatments, a great decrease in ulcer purulence and odor was observed. The treatment was completely tolerable, without any discomfort to the patients. Within one month, the wounds had decreased in depth and showed an obvious increase in granulation tissue. Both patients reported the ulcers were no longer painful and continued daily treatments for six months which completely healed the lesions in the patient who had been advised initially to have an amputation. The second patient showed significant reduction in the wound area during 6 months of electric stimulation therapy.

As in the previous example, one applicator was saturated with sterile water and placed over the ulcer, the other connected to the first was placed nearby on intact skin and had adjustable controls. Current density is 0J50 mA/cm² was used. REFERENCES

The pertinent part of the following references are incoφorated by reference herein:

Bach et al. , The Effect of Electrical Current on Healing Skin Incisions, Env. J. Surg. vol. 157, on 171-74 (1991) Maurer, U.S. Patent No. 4,556,051.

McWhorter, et al , U.S. Patent 5,158,081.

Stephen, U.S. Patent No. 5,344,440.

Tapper, U.S. Patent No. 5,224,927.

Claims

CLAIMS:

1. A method of enhancing healing of a wound comprising the steps of:

placing a first electrode inside of said wound;

placing a second electrode proximate to and apart from said first electrode;

applying an alternating current to said first and second electrodes at a frequency approximately between 0.0027 and 10 Hz and a current density approximately between 0.075 and 0J50 mA/cm².

2. The method of claim 1 wherein said second electrode is placed inside said wound at least about one quarter of an inch from said first electrode to avoid short circuiting.

3. The method of claim 1 wherein said second electrode is placed near and outside of said wound in direct contact with surrounding tissue.

4. An apparatus for healing a wound, said apparatus comprising:

a first electrode designed for placement inside of said wound;

a second electrode separated apart from said first electrode by at least 0.1 inches, but not more than 2 inches; and

an AC power source connected to said first and second electrodes, said power source capable of delivering a current density between about 0.075 mA/cm2 and 0J50 mA/cm2 at a frequency between about 0.0027 and 10 Hz.

5. The apparatus of claim 4 wherein said second electrode is placed inside said wound at least about one quarter of an inch from said first electrode to avoid short circuiting.

6. The apparatus of claim 4 wherein said second electrode is placed near and outside of said wound in direct connect with surrounding tissue.

7. The apparatus of claim 4 wherein said frequency is about 0.0187 Hz.

8. A method of accelerating the healing of a wound on a biological subject, said method comprising the steps of:

conducting an electric current through a surface of said wound in a first direction from a first electrode to a second electrode on said subject; and

intermittently reversing, at a relatively low frequency which prevents skin damage, between approximately 20 times per second and approximately once every three minutes, the polarity of said electrodes to cause electrical current to flow in a second direction opposite to said first direction, whereby electric treatment of said wound may be continuous for extended periods of time.