Functional electrical stimulation (FES) is another form of electrotherapy that utilizes electrical currents to activate nerves that serve extremities affected by paralysis. The goal of FES is to restore function in people with disabilities. There are gait deviations associated with orthotic management, and electrostimulation that is timed to coincide with the individual gait pattern can be a useful addition to many gait training programs. This can take form of a conventional ankle orthosis made of plastic/metal and leather with the addition of electrical stimulation using a remote control switch.
When the clinician chooses electrostimulation as an orthotic substitute, the timing of the stimulus during ambulation is usually controlled by a pressure-activated heel switch. As a result, corrective positioning provided during the swing-through phase will be terminated during stance. The corrected positioning for stance will be terminated during swing-through, producing a more normal gait pattern.
If dorsiflexion during swing-through is the goal of stimulation, there should be no interference with push-off during stance, because weight-bearing on the heel switch during stance would inactivate stimulation of the dorsiflexors. Similarly, where knee extension is stimulated for stance stability, there would be no interference with knee flexion swing-through because non–weight-bearing on the heel switch at end of stance would inactivate stimulation of the quadriceps muscle.
When electrostimulation is used to provide dorsiflexion during swing, the electrical stimulus stops upon weight-bearing, thereby allowing the ankle to move freely into plantar flexion from heel-strike to foot-flat. As a result, no increase in flexion is produced at the knee. This can be important for the hemiparetic patient, where instability is often a problem.
Improving Circulation
Circulation can be improved withNMES by increasing metabolic demand through sporadically activating the muscle pump around the circulatory network. In this application, a low frequency of 20 to 30 pps has been shown to be most effective. A contraction of only 10% to 30% of maximal effort is sufficient. Duty cycle should be one that is not fatiguing; treatment may be given for 10 to 30 minutes and as frequently as is comfortable for the patient (Prentice, 2001; Gersh, 1992; Hayes, 2000).
Healing Wounds
There is now an ample body of evidence supporting the use of electric stimulation for wound healing. Guidelines for the use of stimulation have not been determined for all conditions, yet enough information exists to guide the clinician to a reasonable plan of care. Although not conclusive, a body of evidence suggests that polarity is an important treatment issue for both acute and chronic wounds.
RATIONALE
Literature on wound healing describes the body as having its own bioelectric system, which influences wound healing by attracting the cells of repair and changing cell membrane permeability. When there is a rupture in the skin, a current is generated between the skin and inner tissues that continues until the skin defect is repaired. Healing of the injured tissue is impeded or will be incomplete if these currents no longer flow while the wound is open. A rationale for applying electrical stimulation is that it mimics the natural current of injury and will initiate and/or accelerate the wound healing process.
Electrical stimulation affects each phase of wound healing differently, beginning with the inflammatory phase that initiates the wound repair process. In this phase, increasing blood flow can help in the removal of debris by way of phagocytosis; in addition, by increasing blood flow, electrical stimulation enhances tissue oxygenation.
Next, electrical stimulation has been determined to promote the proliferation phase by stimulating the fibroblasts and epithelial cells needed for tissue repair. Membrane transport is improved, which supports the body's natural current.
Eventually, in the proliferation stage, better collagen is produced, which helps in the stimulation of wound contraction. Clinical studies suggest settings for the proliferation phase with the polarity as negative, pulse rate at 100 to 128 pps, intensity of 100 to 150 volts, and a duration up to 60 minutes, once daily, 5 to 7 times per week.
In the later phase of epithelialization, electrotherapy can stimulate epidermal cell reproduction and migration, helping to produce smoother and thinner scar tissue. Settings during the epithelialization phase include alternating the polarity every 3 days—for example, 3 days negative followed by 3 days positive. Pulse rate is recommended at 64 pps, an intensity of 100 to 150 volts, and a duration of 60 minutes, 5 to 7 times per week.
Based on scientific rationale from early studies, the application of electrical stimulation using direct current reported long treatment times of 20 to 40 hours per week. Four controlled clinical studies and three uncontrolled studies with HVPC reported a mean healing time of 9.5 weeks with 45- to 60-minute treatments, 5 to 7 times per week (Sussman, 2000).
PREPARING THE PATIENT FOR WOUND TREATMENT
Place an electrode over the gauze packing and cover it with a dry gauze pad held in place with bandage tape; this electrode is then connected to the stimulator lead. The other (dispersive) electrode is usually placed proximal to the wound and should be placed over soft tissues, avoiding any bony prominences. A washcloth, wet with water and then wrung out, is placed under the dispersive electrode and held next to the skin with an elasticized nylon strap to allow a good contact at all electrode edges. If the electrode is placed on the back, the weight of the body plus the strap can be used to achieve proper contact at the edges.
FOLLOWING UP ON WOUND CARE
When other topical treatments are required, such as enzymatic debriding agents or antibiotics, the packing must be removed, the topical agent applied, and then the wound redressed. Recently, frequent dressing changes are being discouraged because the changes disturb the wound healing environment by removing important substances in wound exudate and by cooling the wound.
CONTRAINDICATIONS FOR ELECTRICAL STIMULATION
Contraindications include placement of electrodes peripheral to the heart, or using this form of treatment in the presence of a cardiac pacemaker (but see below). Placement of electrodes along regions of the phrenic nerve is contraindicated. Electrical stimulation is contraindicated in the presence of malignancy.
Other contraindications include placement of electrodes over the carotid sinus or the laryngeal musculature, over osteomyelitis, and over topical substances containing metal ions (Sussman, 2000; Gogia, 1995).