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Initially, 4 electronic databases (MEDLINE, CINAHL, EMBASE, and PeDRO) were searched for clinical studies from 1966, or earliest year available on the database to March 2008.
An attempt to identify studies using LIC wound healing was made through the implementation of a search strategy. A combination of the following key words was employed: “low-intensity current,” “low-intensity stimulation,” and “microcurrents” in combination with the key words “wound healing,” “ulcer,” and “ulceration.” References in articles were scanned for additional clinical studies. By scanning references in the retrieved articles, it became clear that in numerous studies, MCs (LIC) were used in treatment but were not defined as such. Instead, they were referred to as “electrical stimulation,” a term that includes LIC as well. This fact led to a new broader search strategy using electrical stimulation as a key word instead of the terms MCs or low-intensity stimulation. Therefore, the key word electric stimulation was also used.
All results from the searches were carefully scanned for studies related to LIC and wound healing.
The final search strategy was conducted by 2 reviewers independently, and final studies retrieved and included in the study (n = 4) were reproduced successfully by a medical doctor and physical therapist not involved in the study.
The inclusion criteria consisted of clinical trials investigating healing of noninfected wounds in human subjects. No restriction on age and date of publication was applied.
Exclusion criteria were as follows:
  • studies investigating healing of infected wounds;
  • studies in languages other than English, German, French, Spanish, and Greek; and
  • high-voltage currents and all other currents other than LIC.
The efficacy of LIC on wound healing has been investigated by several clinical studies on human subjects.
Low-intensity direct current
Low-intensity direct current (LIDC) is the most common type of LIC studied in research. Wolcott et al18 studied wound healing resulting from application of LIDC in 83 patients with ischemic wounds. Three sessions per day took place, each lasting 2 hours. Intensity ranged from 200 to 800 μA, the negative electrode was placed on the wound and the positive electrode proximally. After 3 days, polarity was reversed provided that no infection had appeared. In the event of presence of infection, reversal was postponed until infection had subsided and was then delayed for an additional 3 days. Afterward, polarity was reversed each time healing reached a plateau. The rationale of the delay of polarity reversal may be attributed to the study of Rowley et al,19 where by placing the negative electrode on the wound in similar parameters, the current presented with antimicrobial effects. Forty-five percent of wounds healed completely around a mean of 9.6 weeks, and the rest reached partial healing up to 64.7% over 7.2 weeks. Direct comparison of 2 treatments, standard treatment versus LIC, on the same subjects also took place, a fact that eliminated confounding factors stemming from differences among individuals such as age, sex, general health, and underlying pathology (eg, diabetes). Eight of the patients presented with bilateral wounds. One side was treated with LIDC (n = 8) and the other received standard care (n = 8). Six of 8 LIDC-treated ulcers, completely healed, while the rest 2 of 8 healed up to 70%. In the other side, 3 of 8 ulcers did not heal, 3 of 8 healed less than 50%, and 2 out of 8 healed no more than 75%. In another clinical study,20 LIDC stimulation was applied to 6 patients with bilateral ischemic skin ulcers. The parameters of LIDC were same as in the study by Wolcott et al,18 only polarity was reversed once. One side received standard treatment, whereas the other side ulcer received the same treatment plus LIDC stimulation. The healing rate of the non-LIDC side was 14.7% compared with 30% in the LIDC-treated side. A significant enhancement of healing was observed. A total of 100 patients also received LIDC treatment on ischemic wounds including the six patients previously mentioned. Mean healing rate amounted to 28.4% per week.
The positive effect of LIDC on chronic leg ulcers nonresponsive to other treatment has also been supported in a case study by Assimacopoulos et al,21 in which, LIDC was applied on 3 patients with venous leg ulcers. Healing occurred in all 3 patients in 6 weeks, by applying a current of 100 μA. No control group was available, and being a case study, the strength of the results is somewhat limited.
Carley and Wainapel22 applied LIDC (200–800 μA) on 30 patients with ulcers of various pathologies located over the sacrum or the lower limb below the knee. Patients were assigned in an electrical stimulation treatment group (n = 15) or conventional treatment group (n = 15) matched according to age, diagnosis, etiology, and wound size, thus ensuring that confounding factors were controlled to a considerable extent. Both groups received standard conservative treatment. The treatment group received additional electrical stimulation of 200 to 800 μA for 2 hours, twice daily, with an interval of at least 2 to 4 hours, 5 days per week, for 5 weeks. The negative electrode was placed on the wound and the positive electrode proximally. Reversal of polarity took place, as in the study by Wolcott et al,18 and treatment was continued until full wound healing was reached.
Results demonstrated statistically significant acceleration of wound healing of 1.5 to 2.5 times greater in the LIC group with respect to the conventional treatment group, and furthermore, less debridement was required, as well as less discomfort and resilient scars were observed. Healing was therefore enhanced by LIC stimulation (Table 1).
Table 1Table 1
Low-intensity direct current randomized-controlled trials studies597*
Low-intensity pulsed direct current
Low-intensity current provides minor stimulation to the healing site, being an LIC. One might expect that by using a pulsed form of this current, effectiveness would probably decrease because stimulation might be even less.
In a double-blind study by Wood et al,23 74 patients with stages II and III chronic decubitus ulcers in 4 centers, were randomly allocated in a treatment group (n = 43) and a placebo (sham treatment) group (n = 31), which received standard treatment. Treatment composed of electrical stimulation using low-intensity pulsed direct current (LIPDC) of 300 to 600 μA. After 8 weeks of treatment, 58% of ulcers in the treatment group had healed, whereas in the placebo group only 1 healed, and in the rest of the ulcers, ulcer area increased. A statistically significant accelerated rate of healing (P < .0001) was observed.
Reversal of polarity of pulsed direct current during the healing period has been studied. Junger et al23 investigated the effect of LIPDC on venous leg ulcers of 15 patients who had not responded to standard compression treatment over 79 months. An intensity of 630 μA was selected initially (frequency: 128 pulses per second; pulse duration: 140 μs) with the cathode placed on the wound for 7 to 14 days. The following 3 to 10 days, the positive electrode was positioned on the wound, and after that specific time frame polarity was reversed again. As soon as significant healing had occurred, intensity was reduced to 315μA (64 pulses per second). Treatment was performed on a daily basis, each session lasting 30 minutes. Mean ulcer area was reduced to 63% (P < .01). Furthermore, capillary density was increased to 43.5% (P < .039), and improvement of skin perfusion was observed (PtCo2 = 13.5 increased to 24.7 to 40 mm Hg being normal) (Table 2).
Table 2Table 2
Low-intensity pulsed direct current randomized-controlled trials studies