Synchronization of vagus nerve stimulation with the cardiac cycle of a patient

Abstract

Disclosed herein are methods, systems, and apparatus for treating a medical condition of a patient, involving detecting a physiological cycle or cycles of the patient and applying an electrical signal to a portion of the patient's vagus nerve through an electrode at a selected point in the physiological cycle(s). The physiological cycle can be the cardiac and/or respiratory cycle. The selected point can be a point in the cardiac cycle correlated with increased afferent conduction on the vagus nerve, such as a point from about 10 msec to about 800 msec after an R-wave of the patient's ECG, optionally during inspiration by the patient. The selected point can be a point in the cardiac cycle when said applying increases heart rate variability, such as a point from about 10 msec to about 800 msec after an R-wave of the patient's ECG, optionally during expiration by the patient.

What is claimed: 
     
         1 . A method of treating a medical condition in a patient comprising:
 detecting a portion of a cardiac cycle of the patient;   applying to a vagus nerve of the patient, in response to the detecting of the portion of the cardiac cycle, a pulsed electrical signal comprising a plurality of microbursts, wherein each microburst is characterized by:
 from 2 to 20 pulses per microburst; 
 an interpulse interval between adjacent pulses of the microburst is about 1 to about 20 milliseconds; and 
 a microburst duration of less than 1 second; and 
   wherein each microburst is separated from an adjacent microburst by an interburst period of at least 100 milliseconds.   
     
     
         2 . The method of  claim 1 , wherein the detecting comprises determining a heart rate variability (HRV) parameter, and wherein applying the pulsed electrical signal to the vagus nerve comprises applying the pulsed electrical signal to the vagus nerve in response to the determined HRV parameter. 
     
     
         3 . The method of  claim 1 , further comprising increasing the heart rate variability parameter of the patient by applying the pulsed electrical signal to the vagus nerve. 
     
     
         4 . The method of  claim 1 , wherein the detecting comprises determining an inhibition phase of the cardiac cycle and the applying further comprises not applying the pulsed electrical signal during the inhibition phase of the cardiac cycle. 
     
     
         5 . The method of  claim 4 , wherein applying the pulsed electrical signal comprises applying the pulsed electrical signal after a delay period following detection of an R-wave of the cardiac cycle of the patient, and not applying the pulsed electrical signal for a period of from a remaining portion of the same cardiac cycle to one or more subsequent cardiac cycles. 
     
     
         6 . The method of  claim 1 , wherein the detecting comprises detecting at least a portion of the cardiac cycle selected from a group consisting of a P wave, an R wave, an R-R interval, a QRS complex, a T wave, and an entire PQRST cycle. 
     
     
         7 . The method of  claim 1 , further comprising sensing a temperature of the patient and wherein applying comprises applying the pulsed electrical signal in response to the temperature of the patient. 
     
     
         8 . The method of  claim 1 , further comprising applying a second pulsed electrical signal to the vagus nerve without reference to the cardiac cycle of the patient. 
     
     
         9 . The method of  claim 8 , wherein the second pulsed electrical signal is not a microburst signal. 
     
     
         10 . The method of  claim 1 , wherein the detecting comprises detecting a portion of a respiratory cycle of the patient, and further comprising:
 determining an inhibition phase of the respiratory cycle, and   wherein applying comprises not applying the pulsed electrical signal during the inhibition phase of the respiratory cycle.   
     
     
         11 . The method of  claim 10 , wherein applying the pulsed electrical signal comprises applying the pulsed electrical signal after a delay period following detection of a beginning of inspiration, and not applying the pulsed electrical signal for a period of from a remaining portion of the same respiratory cycle to one or more subsequent respiratory cycles. 
     
     
         12 . The method of  claim 1 , wherein the detecting comprises detecting a portion of a respiratory cycle of the patient and using a high frequency component of a HRV power spectrum to determine when inspiration occurs. 
     
     
         13 . The method of  claim 1 , wherein the detecting comprises detecting the portion of the cardiac cycle of the patient by sensing electrical activity on the vagus nerve and initiating a therapeutic signal when the electrical activity increases. 
     
     
         14 . A method of treating a medical condition in a patient comprising:
 detecting an endogenous electrical activity on a vagus nerve;   applying to the vagus nerve of the patient, in response to the detecting of the endogenous activity on the vagus nerve, a pulsed electrical signal comprising a plurality of microbursts, wherein each microburst is characterized by:
 from 2 to 20 pulses per microburst; 
 an interpulse interval between adjacent pulses of the microburst is about 1 to about 20 milliseconds, and 
 a microburst duration of less than 1 second; and 
   wherein each microburst is separated from an adjacent microburst by an interburst period of at least 100 milliseconds.   
     
     
         15 . The method of  claim 14 , wherein applying the pulsed electrical signal comprises supplementing endogenous vagal activity relevant to a patient's medical condition. 
     
     
         16 . The method of  claim 14 , wherein applying the pulsed electrical signal comprises applying a conventional vagus nerve stimulation signal to the vagus nerve during a first time period and applying the pulsed electrical signal comprising a plurality of microbursts to the vagus nerve during a second time period. 
     
     
         17 . The method of  claim 16 , wherein applying the pulsed electrical signal comprises alternating the conventional vagus nerve stimulation signal and the microburst signal with defined off-time in which no electrical signal is applied to the vagus nerve. 
     
     
         18 . A system for treating a medical condition in a patient comprising:
 a sensor capable of sensing at least a portion of a cardiac cycle of the patient and a respiratory cycle of the patient;   a lead assembly comprising at least one electrode capable of being coupled to a vagus nerve of the patient;   an implantable medical device coupled to the lead assembly and the sensor and comprising:
 a detection unit coupled to the sensor for detecting the portion of the cardiac cycle of the patient and the respiratory cycle of the patient; 
 a controller for controlling an operation of the implantable medical device; 
 a stimulation unit capable of generating and delivering a pulsed electrical signal comprising a plurality of microbursts to the at least one electrode in response to the detection unit detecting the portion of the cardiac cycle and the respiratory cycle of the patient, wherein each microburst is characterized by: 
 from 2 to 20 pulses per microburst; 
 an interpulse interval between adjacent pulses of the microburst is about 1 to about 20 milliseconds; and 
 a microburst duration of less than 1 second; and 
   wherein each microburst is separated from an adjacent microburst by an interburst period of at least 100 milliseconds.   
     
     
         19 . The system of  claim 18 , wherein the detection unit is further configured to determine a heart rate variability (HRV) parameter, and wherein the stimulation unit is further configured to generating and delivering the pulsed electrical signal to the vagus nerve in response to the determined HRV parameter. 
     
     
         20 . The system of  claim 18 , wherein the detection unit is further configured to utilize a high frequency component of a HRV power spectrum to determine when inspiration occurs.