The field of the present invention relates to the delivery of energy impulses (and/or fields) to bodily tissues for therapeutic purposes. The invention relates more specifically to devices and methods for treating conditions associated with stroke and/or transient ischemic attacks. The energy impulses (and/or fields) that are used to treat those conditions comprise electrical and/or electromagnetic energy, delivered non-invasively to the patient
The use of electrical stimulation for treatment of medical conditions is well known. For example, electrical stimulation of the brain with implanted electrodes (deep brain stimulation) has been approved for use in the treatment of various conditions, including pain and movement disorders such as essential tremor and Parkinson's disease [Joel S. PERLMUTTER and Jonathan W. Mink. Deep brain stimulation. Annu. Rev. Neurosci 29 (2006):229-257].
Another application of electrical stimulation of nerves is the treatment of radiating pain in the lower extremities by stimulating the sacral nerve roots at the bottom of the spinal cord [Paul F. WHITE, Shitong Li and Jen W. Chiu. Electroanalgesia: Its Role in Acute and Chronic Pain Management. Anesth Analg 92(2001):505-513; patent U.S. Pat. No. 6,871,099, entitled Fully implantable microstimulator for spinal cord stimulation as a therapy for chronic pain, to WHITEHURST, et al].
Many other forms of nerve stimulation exist [HATZIS A, Stranjalis G, Megapanos C, Sdrolias P G, Panourias I G, Sakas D E. The current range of neuromodulatory devices and related technologies. Acta Neurochir Suppl 97(Pt 1,2007):21-29]. The type of electrical stimulation that is most relevant to the present invention is vagus nerve stimulation (VNS, also known as vagal nerve stimulation). It was developed initially for the treatment of partial onset epilepsy and was subsequently developed for the treatment of depression and other disorders. The left vagus nerve is ordinarily stimulated at a location within the neck by first implanting an electrode about the vagus nerve during open neck surgery and by then connecting the electrode to an electrical stimulator circuit (a pulse generator). The pulse generator is ordinarily implanted subcutaneously within a pocket that is created at some distance from the electrode, which is usually in the left infraclavicular region of the chest. A lead is then tunneled subcutaneously to connect the electrode assembly and pulse generator. The patient's stimulation protocol is then programmed using a device (a programmer) that communicates with the pulse generator, with the objective of selecting electrical stimulation parameters that best treat the patient's condition (pulse frequency, stimulation amplitude, pulse width, etc.) [U.S. Pat. No. 4,702,254 entitled Neurocybernetic prosthesis, to ZABARA; U.S. Pat. No. 6,341,236 entitled Vagal nerve stimulation techniques for treatment of epileptic seizures, to OSORIO et al; U.S. Pat. No. 5,299,569 entitled Treatment of neuropsychiatric disorders by nerve stimulation, to WERNICKE et al; G. C. ALBERT, C. M. Cook, F. S. Prato, A. W. Thomas. Deep brain stimulation, vagal nerve stimulation and transcranial stimulation: An overview of stimulation parameters and neurotransmitter release. Neuroscience and Biobehavioral Reviews 33 (2009):1042-1060; GROVES D A, Brown V J. Vagal nerve stimulation: a review of its applications and potential mechanisms that mediate its clinical effects. Neurosci Biobehav Rev 29(2005):493-500; Reese TERRY, Jr. Vagus nerve stimulation: a proven therapy for treatment of epilepsy strives to improve efficacy and expand applications. Conf Proc IEEE Eng Med Biol Soc. 2009; 2009:4631-4634; Timothy B. MAPSTONE. Vagus nerve stimulation: current concepts. Neurosurg Focus 25 (3,2008):E9, pp. 1-4; ANDREWS, R. J. Neuromodulation. I. Techniques-deep brain stimulation, vagus nerve stimulation, and transcranial magnetic stimulation. Ann. N. Y. Acad. Sci. 993(2003):1-13; LABINER, D. M., Ahern, G. L. Vagus nerve stimulation therapy in depression and epilepsy: therapeutic parameter settings. Acta. Neurol. Scand. 115(2007):23-33; AMAR, A. P., Levy, M. L., Liu, C. Y., Apuzzo, M. L. J. Vagus nerve stimulation. Proceedings of the IEEE 96(7,2008):1142-1151; CLANCY J A, Deuchars S A, Deuchars J. The wonders of the Wanderer. Exp Physiol 98(1,2013):38-45].
Prior art vagal nerve stimulators typically have treatment paradigms that require continuous stimulation of the vagus nerve. The term “continuous stimulate” as defined herein means stimulation that either literally remains ON for 24 hours/day and seven days/week or follows a certain ON/Off pattern continuously for 24 hours/day and seven days/week. For example, existing implantable vagal nerve stimulators “continuously stimulate” the vagus nerve with a typical pattern of 30 seconds ON/5 minutes OFF (or the like) for 24 hours/day and seven days/week. Unfortunately, this not only involves a continuous drain on the power supply of the vagal nerve stimulator, but it makes it very difficult, if not impossible, to provide treatment with a vagal nerve stimulator that is not implanted on the nerve.