Method and apparatus for synchronizing neural stimulation to cardiac cycles

Abstract

A neural stimulator senses a reference signal indicative of cardiac cycles each including a predetermined type timing reference event using a sensor external to the heart and blood vessels. The delivery of the neural stimulation pulses are synchronized to that timing reference event. Examples of the timing reference event include a predetermined cardiac event such as a P-wave or an R-wave detected from a subcutaneous ECG signal, a predetermined type heart sound detected from an acoustic signal, and a peak detected from a hemodynamic signal related to blood flow or pressure.

1 . A neural stimulation system, comprising:
 a stimulation output circuit configured to deliver neural stimulation pulses;   an acoustic sensor configured to sense an acoustic signal indicative of heart sounds;   a heart sound detection circuit coupled to the acoustic sensor, the heart sound detection circuit configured to detect predetermined type heart sounds using the acoustic signal; and   a stimulation control circuit coupled to the stimulation output circuit and the heart sound detection circuit, the stimulation control circuit configured to control the delivery of the neural stimulation pulses and including a synchronization module adapted to synchronize the delivery of the neural stimulation pulses to the predetermined type heart sounds.   
     
     
         2 . The neural stimulation system of  claim 1 , wherein the acoustic sensor comprises an implantable accelerometer. 
     
     
         3 . The neural stimulation system of  claim 2 , wherein the stimulation control circuit comprises an offset interval generator configured to produce an offset interval starting with one of the predetermined type heart sounds and a pulse delivery controller configured to start a delivery of a burst of a plurality of pulses of the neural stimulation pulses when the offset interval expires. 
     
     
         4 . The neural stimulation system of  claim 3 , wherein the heart sound detection circuit comprises one or more of a first heart sound (S1) detector configured to detect S1, a second heart sound (S2) detector configured to detect S2, a third heart sound (S3) detector configured to detect S3, and a fourth heart sound (S4) detector configured to detect S4. 
     
     
         5 . The neural stimulation system of  claim 1 , comprising an implantable medical device including at least the stimulation output circuit, the heart sound detection circuit, and the stimulation control circuit. 
     
     
         6 . The neural stimulation system of  claim 5 , wherein the implantable medical device comprises the acoustic sensor. 
     
     
         7 . The neural stimulation system of  claim 5 , wherein the acoustic sensor comprises an implantable acoustic sensor configured to be connected to the implantable medical device. 
     
     
         8 . The neural stimulation system of  claim 5 , wherein the heart sound detection circuit is configured to average the acoustic signal over a plurality of cardiac cycles and detect the predetermined type heart sounds using the averaged acoustic signal. 
     
     
         9 . The neural stimulation system of  claim 5 , wherein the synchronization circuit comprises a continuous synchronization module configured to synchronize the delivery of the neural stimulation pulses to a heart sound of each of consecutive heart cycles. 
     
     
         10 . The neural stimulation system of  claim 5 , wherein the synchronization circuit comprises a periodic synchronization module configured to synchronize the delivery of the neural stimulation pulses to a heart sound of each of selected heart cycles on a periodic basis. 
     
     
         11 . A method for neural stimulation, comprising:
 delivering neural stimulation pulses;   sensing an acoustic signal indicative of heart sounds;   detecting predetermined type heart sounds using the acoustic signal; and   controlling the delivery of the neural stimulation pulses, including synchronizing the delivery of the neural stimulation pulses to the predetermined type heart sounds.   
     
     
         12 . The method of  claim 11 , wherein delivering the neural stimulation pulses comprises delivering the neural stimulation pulses from an implantable medical device 
     
     
         13 . The method of  claim 12 , wherein sensing the acoustic signal comprises sensing the acoustic signal using an accelerometer. 
     
     
         14 . The method of  claim 12 , wherein sensing the acoustic signal comprises sensing the acoustic signal using a microphone. 
     
     
         15 . The method of  claim 12 , wherein sensing the acoustic signal comprises sensing the acoustic signal using an acoustic sensor incorporated into a lead connected to implantable medical device. 
     
     
         16 . The method of  claim 11 , further comprising:
 producing an offset interval starting with one of the predetermined type heart sounds; and   starting a delivery of a burst of the neural stimulation pulses when the offset interval expires.   
     
     
         17 . The method of  claim 11 , wherein detecting predetermined type heart sounds comprises detecting one or more of a first heart sound (S1) detector to detect S1, a second heart sound (S2) detector to detect S2, a third heart sound (S3) detector to detect S3, and a fourth heart sound (S4) detector to detect S4. 
     
     
         18 . The method of  claim 17 , wherein detecting the predetermined type heart sounds comprises:
 averaging the acoustic signal over a predetermined number of cardiac cycles; and   detecting the predetermined type heart sounds using the averaged acoustic signal.   
     
     
         19 . The method of  claim 11 , wherein synchronizing the delivery of the neural stimulation pulses to the predetermined type heart sounds comprises synchronizing the delivery of the neural stimulation pulses to a heart sound of each of consecutive heart cycles. 
     
     
         20 . The method of  claim 11 , wherein synchronizing the delivery of the neural stimulation pulses to the predetermined type heart sounds comprises synchronizing the delivery of the neural stimulation pulses to a heart sound of each of selected heart cycles on a periodic basis.