Vagal nerve stimulation techniques for treatment of epileptic seizures

#This invention relates to neural tissue stimulation techniques, and more particularly relates to techniques for providing more effective vagus nerve stimulation and for controlling or preventing epileptic seizures with minimized effect on the heart.

#Epileptic seizures are the outward manifestation of excessive and/or hypersynchronous abnormal activity of neurons in the cerebral cortex. Many types of seizures occur. The behavioral features of a seizure reflect function of the portion of the cortex where the hyper activity is occurring. Seizures can be generalized and appearing to involve the entire brain simultaneously. Generalized seizures can result in the loss of conscious awareness only and are then called absence seizures (previously referred to as “petit mal”). Alternatively, the generalized seizure may result in a convulsion with tonic-clonic contractions of the muscles (“grand mal” seizure). Some types of seizures, partial seizures, begin in one part of the brain and remain local. The person may remain conscious throughout the seizure. If the person loses awareness, the seizure is referred to as a complex partial seizure.

#A number of techniques are known to treat seizures including, for example, drug therapy, drug infusion into the brain, electrical stimulation of the brain, electrical stimulation of the nervous system, and even lesioning of the brain. U.S. Pat. No. 5,713,923 entitled Techniques of Treating Epilepsy by Brain Stimulation and Drug Infusion” generally discloses such techniques in the background section and specifically discloses techniques for drug infusion and/or electrical stimulation to treat epilepsy. This patent is incorporated herein by reference in its entirety.

#These and other advantages and features of the invention will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which:

#FIG. 1A is graph illustrating the effects of vagus nerve stimulation on the heart rate for a patient.

#FIG. 1B is a graph of the instantaneous heart rate of a patient as a function of time over an 8 hour period.

#Referring to FIG. 2, a system 10 made in accordance with a preferred embodiment may be implanted below the skin of a patient. System 10 generally includes a sensor 15 for sensing a characteristic of the heart 55 of the patient, a signal generator 20, and one or more stimulation electrodes 25. System 10 may be a modified version of the devices disclosed in the Zabara patents and are incorporated herein by reference.

#Sensor 15 is implemented at or near the heart 55 to sense a characteristic of the heart 55, including the heart rate. A number of techniques may be used to sense the heart rate including, but not limited to, QRS detection or R-wave detection techniques, for example, as disclosed in Antti Ruha et al., “A Real-Time Microprocessor QRS Detector System with a 1-ms Timing Accuracy for the Measurement of Ambulatory HRV,” IEEE Transactions on Biomedical Engineering, Vol. 44, No.3, pp. 159-167 (March 1997). Another technique may use standard analog techniques. In alternative embodiments, sensor 15 may be physically located outside of the body and communicate with the implanted portion through telemetry.

#Sensor 15 is coupled to signal generator 20 via cable 17. Sensor 15 and signal generator 20 may alternatively communicate via telemetry such as, for example, radio-frequency signals. Alternatively, sensor 15 and signal generator 20 may be a single device that may be part of a heart pacemaking or like device. Depending upon the sensor 15 used, the outputs of sensor 15 may require the use of an analog-to-digital (A/D) converter 18 to be coupled between sensor 15 and signal generator 20 as shown in FIG. 3. The output of A/D converter 18 is connected to microprocessor 200 as shown in FIG. 4. Alternatively, if an A/D converter 18 is not required, the output from sensor 15 can be filtered by an appropriate electronic filter 19 prior to delivery of the sensor signal to signal generator 20.