Abstract:
The present invention is related to an implantable medical device for treating breathing disorders and cardiac disorders by delivering stimulation energy to the phrenic nerve, hypoglossal nerves and cardiac muscle tissues.

Description:
CROSS REFERENCE TO RELATED CASES 
       [0001]    The present case claims the benefit of U.S. Provisional Application 60/881,695 filed Jan. 22, 2007 entitled Trnasvenous Stimulation of Hypoglossal Nerve to Treat Central and Obstructive Sleep Apnea. The disclosure of the provisional application is incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    An implantable medical device and a method carried out with an implantable medical device for the treatment of sleep apnea and for the treatment of sleep apnea in patients with cardiac disorders. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sleep apnea (SA) is a disease state in which the patient exhibits periodic breathing. Sleep apnea is typically characterized as either “obstructive” (OSA) or “central” (CSA). Many patients exhibit the disorder in both of its forms, OSA and CSA. OSA is traditionally treated by attempting to maintain patency of the upper airway. CSA is traditionally treated by stimulation of the diaphragm. Sleep apneas occur with high frequency in patients with cardiac rhythm disorders that might be treated with bradycardia treatment or biventricular pacemakers. 
       SUMMARY 
       [0004]    The present invention includes a method, device, and system for treatment of SA breathing. The system includes one or more transvenous leads coupled to an implanted medical device, where one lead system is positioned to stimulate a muscle group. An additional lead system is positioned to stimulate at least one nerve. In an alternative embodiment of the device, the two lead systems both stimulate nerves. In this alternative embodiment, one set of nerves leads to muscle contraction and the other set of nerves do not lead to muscle contraction but they locally alter the “tone” of the nervous system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0005]      FIG. 1  depicts the system in schematic form; 
           [0006]      FIG. 2  depicts a process carried out in the implanted device; 
           [0007]      FIG. 3  depicts a process carried out in the implanted device; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    The nervous system (NS) is exceedingly complex. Two main components of the NS are the sympathetic NS and the parasympathetic NS. It is widely held that these two systems counteract each other and a homeostatic balance is achieved between them. It is recognized that the relative activation of the two systems results in a “tone” that that varies between waking and sleeping states. 
         [0009]    Without elucidating a complete mechanism of action, the inventors completed a course of experimentation that suggests to them that transvenous stimulation near the base of the tongue, near the location of the hypoglossal nerves, increases airflow during apnea with out actually provoking activation of muscle tissue near the stimulation site. Applicants believe that this sub-threshold stimulation alters “tone”. It should be understood that the measurement of tone is fraught with technical difficulties; However, the inventors beleive that the periodic and episodic application of electrical currents at voltages and currents far below the levels required for evoked muscle contraction of tissue near the tongue are responsible for an increase in the diameter of the airway passages and increase ventilation in patients. The inventors believe that episodic background simulation may increase the otherwise prevailing level of tone and that this level of stimulation is compatible with restful sleep and will not arouse a sleeping patient. In each embodiment of the inventors&#39; system low-level stimulation is travenously delivered to nerves and muscles near the hypoglossal tissues of a patient. 
         [0010]      FIG. 1  depicts an implanted medical device  10  (IMD) of the type necessary to carry out the invention. The IMD  10  is coupled to a first transvenous lead system  12  located in the area of the tongue near the hypoglossal nerves represented schematically at reference numeral  17  and placing stimulation electrodes typified by electrode  23  in a vein or artery  13  near the hypoglossal nerves  17 . A second lead system  14  couples the IMD  10  transvenously to the phrenic nerve and diaphragm represented schematically at reference numeral  19 . Once again stimulation electrodes are placed near the phrenic nerve as indicated schematically at reference numeral  25 . A third lead system  16  places a pacing lead  20  in the right ventricle RV and a pacing lead  18  positioned to stimulate the left ventricle LV of the heart  21 . 
         [0011]    The IMD  10  contains conventional circuitry to detect the patients R-wave and impedance plythesmographic detectors to find the mid-breath point in the respiration cycle. The IMD  10  also contains an activity sensor to measure the activity level of the patient. This activity sensor may be used to detect periods of sleep. These sense amplifiers, stimulation pulse generators, activity monitors, and impedance monitors are structures that are not described in detail as they are well known to those skilled in this art. 
       Pacing Embodiment 
       [0012]    The transvascular subtheshold low level stimulation of the hypoglossal tissues near the upper airways may be combined with conventional bradycardia pacing therapies. Applicants describe a device that combines low-level transvascular stimulation with a conventional pacing regime or modality. Although the invention is applicable to both biventricular lead placements as well as cardiac defibrillator lead placements, the invention is described in the context of a biventricular demand mode pacemaker. It must be understood that other bradycardia and tachycardia treatment modalities are contemplated and are within the scope of the claims. The choice of the depicted modality is selected for simplicity and because it is indicated for patients likely to also suffer from sleep apnea. 
         [0013]    During periods of pacing support of the patient&#39;s rhythm the IMD  10  will also delivers stimulation energy to the hypoglossal tissues via the transvenous lead  12 . The stimulation energy delivered may be continuous or intermittent at an appropriate relatively low frequency duty cycle. 
         [0014]    At times when the patient&#39;s detected activity is low, the IMD may deliver background stimulation from an appropriate pulse generator within the IMD  10  through the lead system  12  at a level insufficient to arouse the patient from sleep. 
         [0015]      FIG. 2  is a flowchart depicting representative implementation of the integration of very low energy transvascular hypoglossal stimulation with brady pacing. The process starts with block  100 . In decision block  120  the presence or absence of an R-wave is determined with a sense amplifier within the IMD  10 . If an R-wave is detected (yes in process  120 ), the process  120  resets the pacing escape interval timer and returns to the start of R-wave detection process  120 . If an R-wave does not occur within an escape interval (no in process  120 ), the process moves to process  122  where patient activity is monitored. If the patient is inactive (no in process  122 ), perhaps asleep, and in need of ventricular stimulation, then the processes  124  activates the low level hypoglossal tissues via lead system  12 , while process  126  activates the biventricular pulse generators to delivery stimulation on leads  18  and  20 . In this fashion the patient receives the low level hypoglossal stimulation in phase with pacing therapy. Other variations in stimulation patterns are possible as well. 
       Respiration Embodiment 
       [0016]    The IMD  10  is equipped to detect respiration and deliver stimulation to the phrenic nerve via lead system  14  at times and stimulation magnitudes to “hold” the breath of a patient. This breath holding attribute tends to decrease breathing rate and has been proposed by the inventors as a treatment for central sleep apnea. 
         [0017]    In this embodiment low-level electrical stimulation of the tissues near the hypoglossal nerve is invoked and delivered at the time that phrenic nerve receives stimulation.  FIG. 3  depicts a representative implementation of a software process carried out within the IMD  10  to treat a patient. In the start process  101  the IMD  10  turns on the respiration sensor system, and in process  130  the IMD finds the mid-breath point. If appropriate (yes in process  130 ), the IMD enters process  132  where pulse generators within the IMD deliver phrenic nerve stimulation via lead system  14  in synchrony with the mid breath respiration point. The device moves to process  134  where low-level hypoglossal stimulation is delivered via lead system  12 . In this fashion low-level electrical energy is delivered to the upper airway to improve patency during a breath. In this way the invention overcomes limitations of prior art that require:
       1. surgical placement of nerve stimulation electrodes on the nerve   2. synchronized stimulation that requires contraction of selected airway muscles prior and during natural inspiration phase of the breath   3. discomfort to the patient caused by stimulation of small muscles in the head and neck