Physical therapists, chiropractors, and other medical providers have used nerve and muscle stimulation to treat a variety of ailments. These medical providers have used electronic muscle stimulation (EMS) and transcutaneous electrical nerve stimulation (TENS) as a treatment for muscle and joint rehabilitation as well as chronic pain. Urologists and obstetrician/gynecologists have used a form of TENS for pelvic floor stimulation to treat incontinence and pelvic pain. In addition, medical providers have used a variety of implantable and percutaneous stimulators to manage pain, to create local nerve blocks, and to treat incontinence, Parkinson""s disease, and multiple sclerosis.
Transcutaneous stimulators, i.e., stimulators which do not physically penetrate the skin surface, are less invasive than percutaneous and implantable stimulators. However, transcutaneous stimulators often require higher current levels than percutaneous and implantable stimulators. Higher current levels can cause irritation and discomfort when used for extended periods. Also, since transcutaneous stimulators stimulate on the skin surface, their target site usually covers a large area. Thus, transcutaneous stimulators may not be highly effective for direct nerve stimulation.
More typically, providers use implantable stimulators when there is a need for direct nerve stimulation or continuous stimulation. Implantable stimulators can free a patient from the need for constant and frequent manual treatment. However, implantable stimulators can cause mild discomfort, and often cause more severe implant-site pain.
Percutaneous stimulators provide direct nerve stimulation without the invasiveness of an implant. However, traditional percutaneous stimulators need to be in close proximity to a target nerve. Movement of the stimulating needle can result in a loss of the ability to stimulate a target nerve. A medical provider often needs to re-insert and/or re-locate the percutaneous needle during treatment. In addition, the load impedance provided by sub-cutaneous tissue is low. Such low impedance can result in unwanted or accidental transmission of relatively high current levels. Such relatively high current levels can result in nerve and tissue damage.
It is an object of the invention to provide stimulator systems and methods that provide the non-invasiveness of transcutaneous systems with the effectiveness of percutaneous systems.
It is another object of the invention to provide systems and methods that are less likely to result in nerve and tissue damage.
It is yet another object of the invention to provide inexpensive and durable electro-nerve stimulation systems.
Other general and more specific objects of this invention will in part be obvious and will in part be evident from the drawings and the description which follow.
In one aspect, the present invention is directed to transcutaneous-percutaneous electro-nerve stimulator systems and methods that are minimally invasive and that are effective in direct nerve stimulation. A system according to one aspect of the invention includes a pulse generator, a transcutaneous electrode electrically coupled to the pulse generator, and a percutaneous electrode electrically coupled to the pulse generator and having an end for insertion into a patient""s body. The pulse generator produces pulses which couple between the transcutaneous electrode and the percutaneous needle. The transcutaneous electrode is positioned proximate to the selected stimulation site on the surface of the skin. Preferably, the transcutaneous electrode is positioned distal from the stimulation site. The percutaneous electrode is inserted through the skin in proximity to an internal stimulation site, preferably in proximity to the nerve to be stimulated. The pulses from the pulse generator traverse the internal stimulation site by passing between the transcutaneous electrode and the internal percutaneous electrode.
In another aspect of this invention, the transcutaneous electrode allows for maximum current dispersion at the application site. In one embodiment, an internal layer of the electrode is coated with a high conductive metal, such as silver, to disperse the stimulating current quickly over the entire electrode surface.
In another aspect of this invention, since the direction of the electric field can reduce the required intensity, the system includes a mechanism to assure a particular polarity of the stimulating current. According to this aspect of the invention, the system has a transcutaneous electrode that is fixedly attached to the first lead wire. In addition, the first and second lead wires are combined at one end into a single cable for interfacing with the pulse generator. The cable is xe2x80x9ckeyedxe2x80x9d to interface with the pulse generator so that the transcutaneous electrode is always positive and the percutaneous electrode is always negative. In other words, the cable can be plugged into the pulse generator in only one way.
In another aspect of this invention, the electrical circuit of the pulse generator has an AC coupled current pulse output, and includes an element for measuring the amount of current delivered directly to the patient. Patient stimulators are safest when the output circuitry is AC coupled. AC coupled circuits guarantee that no net DC current will pass to the body. Traditional stimulators have accomplished an AC coupled output using a current transformer. A system according to one embodiment of the present invention includes circuitry which creates an AC coupled output without the need for a current transformer by using a DC blocking capacitor in conjunction with the following circuit features: a pulse shaping circuit, a DC-DC step up voltage source, a switching circuit, and a current sense/stimulation adjustment feedback control.
In another aspect of this invention, the circuitry includes a discharge path for the DC blocking capacitor which has an optimal discharge time-constant to accommodate the desired pulse width, duty cycle, and expected load range of the output pulse. A capacitor can serve as a DC block yet pass current pulses with sufficiently fast rise and fall times. However, after a number of pulses the capacitor can become charged if a discharge path is not provided. This accumulated charge voltage effectively subtracts from the available supply voltage so little or no pulse energy is delivered to the load. The discharge path in this circuitry is preferably designed to minimize droop during the output pulse yet assure full discharge by the time of the next pulse arrives.
In another aspect of this invention, the pulse generator circuitry includes the option of an active or passive discharge configuration. In the passive configuration, a discharge resistor can be included in the output circuit parallel to the DC blocking capacitor and output load. In the active configuration, a transistor type switch can be used to discharge the blocking capacitor. The switch can momentarily discharge the capacitor when the output pulse is not active.
In another aspect of this invention, the electrical output circuit has the frequency and pulse width fixed to a value optimal for a given application. The electrical output circuit only allows a user to adjust the stimulation current threshold. Thus the electrical output circuit prevents the user from setting the parameters to values that are sub-optimal or even harmful while making the device easier to use.
In another aspect of this invention, the percutaneous electrode can be in the form of a needle having a portion coated or insulated to allow for more precise stimulation points. In one embodiment, a portion of the needle shaft is covered or coated with an electrically-insulating material, while the needle tip is exposed to permit electrical contact with the patient""s tissue.
In another aspect of this invention, the pulse generator is battery powered and is small enough to be comfortably worn or carried by the patient. For example, the pulse generator can be small enough to be worn around a leg or other body extremity using a small wrap similar to a blood pressure cuff.