fig1 - 3 illustrate a chronically implantable lead 21 , which is employed to stimulate surgically adapted skeletal muscle to contract as part of a bioelectrical stimulating device performing neuromuscular stimulation to provide cardiac assistance . a connector 122 is attached to the proximal end portion of the lead 21 to provide coupling between an implantable bioelectrical stimulating device 1 ( see fig9 ) and the lead 21 . two sealing rings 124 are mounted upon the connector 122 to seal the connection between the lead 21 and the implantable bioelectrical stimulating device against intrusion of biological fluids . in the illustrative embodiment of the invention , a terminal 126 includes five terminal pin connector elements 132 , 134 , 136 , 138 and 140 to electrically couple the lead 21 to the implantable bioelectrical stimulating device . each of the pin connector elements is electrically connected to a corresponding helical conductor within the lead 21 which extends to the distal end portion of the lead , where the insulation 150 surrounding each conductor is broken to form an electrode . thus , electrodes 112 , 114 , 116 , 118 and 120 are electrically connected with terminal pin connector elements 132 , 134 , 146 , 138 and 140 via conductors 112a , 114a , 116a , 118a and 120a , respectively . an insulating sheath 128 provides electrical insulation to the lead 21 , preventing electrical currents from flowing between the lead 21 and body fluids . each conductor within the lead 21 is also individually insulated . a transition sleeve 130 marks the boundary between the insulated portion 128 of the lead 21 and the distal electrically conductive electrode portion of the lead 21 . electrodes 112 , 114 , 116 , 118 and 120 are portions of the conductors in lead 21 , which make electrical contact to biological tissue by virtue of a break in the individual insulation of each conductor . electrodes 112 , 114 , 116 , 118 and are composed of platinum or a platinum iridium alloy . furthermore , the insulating sheath 128 does not extend to the region of the lead 21 in the vicinity of the electrodes . upon implantation of the lead 21 , imbedded sutures located within a notch 142 in the suture sleeve 130 may be used to secure the lead . a suture strand 144 , made of a polymer material such as polypropylene , is affixed to the lead and extends from its proximal end throughout the length of the lead to the distal end of the lead , where it is attached to an insertion needle 146 . the suture strand 144 is situated within the center of the lead 21 . as best seen in fig2 and 3 , helical conductor 120a encircles the suture strand 144 and terminates in the electrode 120 at the distal end of the lead 21 , where the insulating polymer material 150 enveloping the conductor is broken . similarly , helical conductor 118a overlies the insulating material covering the electrode 120 and comprises the electrode 118 at the distal end portion of the lead 21 . in a like manner , a cylindrical layer of insulating polymer material 150 overlies the conductor for the electrode 118 . the remaining helical conductors 116a , 114a and 112a , which terminate in the electrodes 116 , 114 and 112 , respectively , are each separated and overlaid by a cylinder of insulating polymer material 150 . overlying each of the concentric cylindrical layers of conductors and insulating material is the insulating sheath 128 . at the distal end of the lead 21 , the insulating sheath 128 and the outer layer of the insulating polymer material 150 do not extend beyond the suture sleeve 130 ( shown in fig1 ), exposing the outer conductor to provide the electrode 112 . beyond the electrode 112 the insulating material 150 underlying conductor 112a tapers distally to the next interior conductor 144a that is exposed to provide the electrode 114 . the insulating material 150 underlying each successive conductor 114a , 116a and 118a tapers distally to the next interior conductor cylinder , exposing electrodes 116 , 118 and 120 , respectively . alternatively , the insulated helical conductors 112a , 114a , 116a , 118a and 120 a may extend and electrically couple to corresponding conductive cylindrical sleeves ( not shown ), or other conductive elements , which serve as electrodes 112 , 114 , 116 , 118 and 120 . fig4 is an illustration of a chronically implantable lead 21 , which is similar to the lead of fig1 but provides for both negative and positive electrodes for each channel , which electrodes are positioned in respective negative and positive distal portions 21 - and 21 + of the lead . similar to fig1 a connector 122 is attached to the proximal end of the lead 21 to provide coupling between an implantable bioelectrical stimulating device 1 ( fig9 ) and the lead 21 . two sealing rings 124 are mounted upon the connector 122 to seal the connection between the lead 21 and the implantable bioelectrical stimulating device . a terminal 126 includes ten terminal pin connector elements 132 +, 132 -, 134 +, 134 -, 136 +, 136 -, 138 +, 138 -, 140 + and 140 - to electrically couple the lead 21 to the implantable bioelectrical stimulating device . each of the pin connector elements is electrically connected to a corresponding conductor ( not shown ) within the lead 21 which extends to the distal end of the lead , where the insulation 150 + and 150 - for each conductive element is broken to form an electrode . thus , electrodes 112 +, 112 -, 114 +, 114 -, 116 +, 116 -, 118 +, 118 -, 120 + and 120 - are electrically connected with terminal pin connector elements 132 +, 132 -, 134 +, 134 -, 136 +, 136 -, 138 +, 138 -, 140 + and 140 -, respectively . an insulating sheath 128 provides electrical insulation to the lead 21 . each conductor within the lead 21 is also individually insulated . a transition sleeve 130 marks the boundary between the insulated portion 128 of the lead and the distal electrically conductive electrode portion of the lead 21 . electrodes 112 +, 121 -, 114 +, 114 -, 116 +, 116 -, 118 +, 118 -, 120 + and 120 - are portions of the conductors in lead 21 , which make electrical contact to biological tissue by virtue of a break in the individual insulation of each conductor . the electrodes are composed of platinum or a platinum iridium alloy . fig5 is an illustration of a chronically implantable lead 21 , which is similar to the lead of fig4 but provides for a single negative electrode 112 -, positioned in the negative distal portion 21 - of lead 21 , that is shared by all channels . similar to fig4 a connector 122 is attached to the proximal end of the lead 21 to provide coupling between an implantable bioelectrical stimulating device 1 ( fig9 ) and the lead 21 . two sealing rings 124 are mounted upon the connector 122 to seal the connection between the lead 21 and the implantable bioelectrical stimulating device . a terminal 126 includes six terminal pin connector elements 132 +, 134 +, 136 +, 138 +, 114 + and 132 - to electrically couple the lead 21 to the implantable bioelectrical stimulating device . each of the pin connector elements is electrically connected to a corresponding conductor within the lead 21 which extends to the distal end of the lead , where the insulation 150 for each conductive element is broken to form an electrode . thus , electrodes 112 +, 112 -, 114 +, 116 +, 118 + and 120 + are electrically connected with terminal pin connector elements 132 +, 132 -, 134 +, 136 +, 138 + and 140 +, respectively . an insulating sheath 128 provides electrical insulation to the lead 21 . each conductor within the lead 21 is also individually insulated . a transition sleeve 130 marks the boundary between the insulated portion 128 of the lead 21 and the distal electrically conductive electrode portion of the lead 21 . electrodes 112 +, 112 -, 114 +, 116 +, 118 +, and 120 + are portions of the conductors in lead 21 which make electrical contact to biological tissue by virtue of a break in the individual insulation of each conductor . the electrodes are composed of platinum or a platinum iridium alloy . fig6 depicts a block diagram of a five channel skeletal muscle stimulator 20 for electrically driving the electrodes 112 +, 112 -, 114 +, 114 -, 116 +, 116 -, 118 +, 118 -, 120 + and 120 - in lead 21 of fig4 . the five channel skeletal muscle stimulator 20 would supply stimulating voltages for two identical leads 21 , corresponding to the positive and negative lead portions 21 + and 21 - of fig4 if the stimulator is connected with leads such as those illustrated in fig1 . the electronic circuits for muscle stimulator channels i through v , blocks 210 , 211 , 212 , 213 and 214 , respectively , are identical , as disclosed in the drawing and description of fig7 hereinafter . the skeletal muscle stimulator 20 receives input signals from a microprocessor 19 ( fig9 ) over a skeletal muscle stimulation control bus 22 . these signals designate the channel to be activated , as well as the amplitude , timing and polarity of the stimulus pulses to be generated . muscle stimulator channel i 210 generates neuromuscular stimulating pulses that drive the terminal pin connector elements 132 + and 132 -, which activate the electrodes 112 + and 112 - in lead 21 . likewise , muscle stimulator channel ii 211 drives terminal pin connector elements 134 + and 134 - and electrodes 114 + and 114 -, muscle stimulator channel iii 212 drives terminal pin connector elements 136 + and 136 - and electrodes 116 + and 116 -, muscle stimulator channel iv 213 drives terminal pin connector elements 138 + and 138 - and 118 +[ and 118 -, and muscle stimulator channel v 214 drives terminal pin connector elements 140 + and 140 - and electrodes 120 + and 120 -. fig7 illustrates a circuit schematic of one channel of the five channel skeletal muscle stimulator 20 , for example channel i 210 , which electrically drives electrodes 112 + and 112 - of fig4 . each channel of skeletal muscle stimulator 20 receives input signals from microprocessor 19 over skeletal muscle stimulation control bus 22 . these signals include a power input vdd , which is typically an amplitude of 2 . 8 v , and a ground reference vss , as well as control signals s -- l , 2x -- l , d -- l , xchb -- l and m 13 on -- h . a pacemaker 17 ( fig9 ) supplies battery power b -- pos and b -- neg which provides energy for biphasic skeletal muscle stimulation . in the preferred embodiment of the present invention , the b -- pos amplitude is about 3 v . the battery voltages b -- pos and b -- neg are floating with respect to circuit power vdd to prevent variations in circuit energy during different parts of the cardiac cycle caused by inconsistent demands on the battery from the pacing pulse and skeletal muscle stimulation pulse generation circuits . xchb -- l , a cross channel blanking control signal from the microprocessor 19 , is also supplied to a sense blanking input ( not shown ) of the pacemaker 17 to disable pacemaker sensing during generation of a skeletal muscle stimulation pulse . this prevents the pacemaker 17 from incorrectly classifying a skeletal muscle stimulation pulse as an episode of intrinsic cardiac activity . the circuit of fig7 in response to codes written from the microprocessor 19 , produces biphasic skeletal muscle stimulation pulses on the skeletal muscle lead , m + and m -. biphasic cathodic pulses are preferred to monophatic pulses to minimize electrochemical damages at the electrode site . all characteristics of the skeletal muscle stimulation pulses -- the timing , frequency , burst duration , amplitude , pulse width , and pulse morphology -- are determined by the microprocessor . fig7 circuitry merely responds to these input codes by producing a particular amplitude and polarity signal on the m + and m - leads . in this manner , the microprocessor generates the characteristics of the skeletal muscle stimulation pulses according to the timing of codes written to the skeletal muscle stimulation control bus 22 . input signal lines s -- l , m -- on -- h and xchb -- l contain skeletal muscle pulse enable and polarity control signals which are dynamic in the sense that the microprocessor 19 defines the code to be written and the time duration that a particular code will be sustained , writes the codes to the skeletal muscle stimulation control bus 22 , writes predetermined time duration information to a timer within the processor ( timer i , 51 , or timer ii , 52 , of fig1 ), waits for a timer wakeup and initiates the next code . the microprocessor enables the circuit of fig7 to produce an output on one or the other of leads m + and m - by setting input signal line m -- on -- h to &# 34 ; 1 &# 34 ; which , by means of control by p - channel switching field effect transistor q3 , applies either b -- pos or b -- neg battery power to the corresponding leads m + and m -, depending on the signal on input signal line s -- l . the microprocessor controls the stimulus pulse timing and width by setting a signal on input signal line s -- l for a predetermined time and duration . when microprocessor 19 writes a &# 34 ; 0 &# 34 ; value to input signal line s -- l while a &# 34 ; 1 &# 34 ; value is on input signal line m -- on -- h , the outputs of p - channel switching field effect transistors q7 and q8 are enabled to enable the m + lead , and the outputs of n - channel switching field effect transistors q10 and q11 are disabled to disable the m - lead , producing a positive polarity output pulse on the lead m +, having a duration r , as shown at 62 in fig8 . the stimulus duration r is a programmable parameter for the microprocessor . alternatively , the microprocessor ay write a &# 34 ; 1 &# 34 ; value to line s -- l to disable field effect transistors q7 and q8 and enable transistors q10 and q11 , while a &# 34 ; 1 &# 34 ; value is on line m -- on -- h , to produce a negative polarity output pulse on the lead m -, having a duration s , as shown at 63 in fig8 . the stimulus duration s is a programmable parameter for the microprocessor . if the value applied to input signal line m -- on -- h is &# 34 ; 0 &# 34 ;, neither lead m + nor lead m - are energized and the skeletal muscle stimulator does not produce a pulse . as indicated earlier , microprocessor 19 controls cross blanking control signal line xchb -- l to set the timing and duration of the sense blanking input to the pacemaker 17 in order to disable pacemaker sensing during generation of a skeletal muscle stimulation pulse . cross channel blanking duration may be a programmable parameter for the microprocessor . in an embodiment of the invention in which the lead 21 has multiple positive electrodes 112 +, 114 +, 116 +, 118 + and 120 +, and only a single negative electrode 112 - ( see fig5 ) is attached to a bioelectrical device having multiple channels ( see fig7 ), all of the negative channels ( m -) of the circuit are connected with the common negative terminal pin connector 132 - of terminal 126 . in this case the microprocessor 19 is programmed so that only a single negative channel m - of the multiple channels may be energized at one time . input signal lines d -- l and 2x -- l contain skeletal muscle pulse amplitude control signals which are static in the sense that microprocessor 19 writes them , at most , only once per cycle . normally , the microprocessor only writes amplitude control signals upon reprogramming , via telemetry , by an external communicating device . line d -- l is utilized as a battery voltage doubler . line 2x -- l is utilized as a stimulus voltage doubler . thus , lines d -- l and 2x -- l remain at the same settings throughout numerous cardiac cycles , while the skeletal muscle pulse that is generated has a negative , positive or zero polarity . when the microprocessor sets line d -- l to &# 34 ; 1 &# 34 ; (&# 34 ; on &# 34 ;), the n - channel switching field effect transistor q enables doubling of the battery voltage . in a similar manner ( but with an opposite polarity ), when the microprocessor sets line 2x -- l to &# 34 ; 0 &# 34 ; (&# 34 ; on &# 34 ;), the p - channel switching field effect transistor q9 enables doubling of the stimulus voltage . therefore , when the microprocessor sets line d -- l &# 34 ; off &# 34 ; ( 1 ) and line 2x -- l &# 34 ; off &# 34 ; ( 1 ), the amplitude of the skeletal muscle stimulation pulse is equal to the battery voltage , 3 v in the preferred embodiment of the invention . when the microprocessor sets line d -- l &# 34 ; on &# 34 ; (&# 34 ; 1 &# 34 ;) and line 2x -- l &# 34 ; off &# 34 ; (&# 34 ; 1 &# 34 ;), the amplitude of the skeletal muscle stimulation pulse is equal to twice the battery voltage ( 6 v ). when the microprocessor sets line d -- l &# 34 ; on &# 34 ; (&# 34 ; 1 &# 34 ;) and line 2x -- l &# 34 ; on &# 34 ; (&# 34 ; 0 &# 34 ;), the amplitude of the skeletal muscle stimulation pulse is equal to four times the battery voltage ( 12 v ). referring to fig9 when the microprocessor 19 determines that skeletal muscle graft stimulation is appropriate , it works in conjunction with the skeletal muscle stimulator 20 to produce pulses or bursts of pulses , which are applied to the skeletal muscle graft 9 . the microprocessor may time these pulses or bursts of pulses with respect either to intrinsic or to paced cardiac activity which is sensed or generated , respectively , by the pacemaker 17 . this mode of skeletal muscle stimulation is termed &# 34 ; synchronous &# 34 ; skeletal muscle stimulation . alternatively , the microprocessor 19 may time the pulses or bursts of pulses according to the operations of an internal timer , wherein the stimulation occurs asynchronously with respect to individual cardiac events . according to &# 34 ; synchronous &# 34 ; programming of the microprocessor 19 , when the pacemaker 17 detects either a natural atrial or a natural ventricular intrinsic event it will send a signal to the microprocessor 19 via atrial sense line 45 or ventricular sense line 49 . the microprocessor 19 may be programmed to respond to such a signal by generating skeletal muscle stimulation . alternatively , in the event that the patient &# 39 ; s natural heart rate falls below a predetermined rate , then the microprocessor will send an atrial pace control signal on line 46 , a ventricular pace control signal on line 50 , or both signals , to the pacemaker 17 to generate a pacing pulse to the heart . in addition , the microprocessor 19 , may be programmed to trigger skeletal muscle stimulation after such a pacing event . programming of synchronous operation of the skeletal muscle stimulator includes the specification of a synchronization ratio which determines the ratio of cardiac events for each skeletal muscle stimulation burst . the microprocessor 19 resets a cardiac event counter with each initiation of a skeletal muscle stimulation burst and increments the counter with each subsequent cardiac event . for each skeletal muscle stimulation burst , the microprocessor 19 waits a predetermined and programmed delay interval before initiating the burst . other programmed parameters which may be utilized are an interpulse interval ( the time between sequential pulses ), the stimulus duration , the recharge duration , the cross - channel blanking duration and a maximum muscle stimulation rate . all or some of these parameters may have preprogrammed sets of values which depend on the rate at which the heart is beating . an interpulse interval determines the time intervals between each individual pulse within a burst of pulses . a burst frequency is the reciprocal of the interpulse interval . the maximum muscle stimulation rate is an upper rate boundary of synchronization of cardiac and muscle stimulation activity . upon a cardiac event occurring at cardiac rates faster than the maximum muscle stimulation rate , the microprocessor will fail to generate skeletal muscle stimulation but will , instead , stimulate the skeletal muscle based upon triggering by the next subsequent cardiac event . referring to fig9 there is depicted a block diagram of a bioelectrical stimulating device 1 . device 1 is designed to be implanted within a patient and includes a pulse module 10 and appropriate leads for connecting module 10 to a patient &# 39 ; s heart 11 . more particularly , device 1 may include an atrial cardiac lead 12 extending to the atrium of the patient &# 39 ; s heart for the administration of therapy to the atrium , and generally will include a ventricular cardiac lead 13 extending to the ventricle of the patient &# 39 ; s heart for the administration of therapy to the ventricle . device 1 generally also includes a pacemaker 17 for the detection of analog signals representing cardiac electrical activity and for the delivery of pacing pulses to the heart ; a microprocessor 19 which , in response to various inputs received from the pacemaker 17 , performs various operations so as to generate different control and data outputs to pacemaker 17 and to skeletal muscle stimulator 20 ; and a power supply 18 for the provision of a reliable voltage level to pacemaker 17 , microprocessor 19 and skeletal muscle stimulator 20 by suitable electrical conductors ( not shown ). skeletal muscle stimulator 20 generates electrical pulses on a skeletal muscle lead 21 for stimulating a skeletal muscle graft 9 , such as a patient &# 39 ; s latissimus dorsi muscle , according to timed control signals from microprocessor 19 communicated via skeletal muscle stimulation control bus 22 . microprocessor 19 is connected to a random access memory / read only memory ( ram / rom ) unit 121 by an address and data bus 123 . an end - of - life ( eol ) signal line is used to provide , to microprocessor 19 , a logic signal indicative of the approach of battery failure in power supply 18 . as more fully described below , microprocessor 19 and pacemaker 17 are connected by a communication bus 42 , the atrial sense line 45 , the atrial pace control line 46 , an atrial sensitivity control bus 43 , an atrial pacing energy control bus 44 , the ventricular sense line 49 , the ventricular pace control line 50 , a ventricular sensitivity control bus 47 , and a ventricular pacing energy control bus 48 . microprocessor 19 transmits control signals , according to the description below , over skeletal muscle stimulation control bus 22 to the skeletal muscle stimulator 20 . referring to fig1 , pacemaker 17 comprises circuitry for atrial pacing 24 , ventricular pacing 34 , atrial sensing 25 , ventricular sensing 35 , and telemetry 30 . in addition , pacemaker 17 includes a control block 39 which includes an interface to microprocessor 19 . in operation , sensing circuits 25 and 35 detect respective atrial and ventricular analog signals 23 and 33 from the heart 1 and convert the detected signals to digital signals . in addition , the sensing circuits 25 and 35 receive an input atrial sense control 27 and an input ventricular sense control 37 , respectively , from the control block 39 which determines the sensitivity applied to the detection circuit . atrial pacing circuit 24 receives from control block 39 , via an atrial pacing control bus 28 , an atrial pace control input and an atrial pacing energy control input . similarly , ventricular pacing circuit 34 receives from control block 39 , via a ventricular pacing control bus 38 , a ventricular pace control input and a ventricular pacing energy control input . the atrial and ventricular pace control inputs determine the respective types of atrial and ventricular pacing to be delivered to the heart via an atrial pacing pulse lead 31 and atrial cardiac lead 12 , and via a ventricular pacing pulse lead 32 and ventricular cardiac lead 13 , respectively . the atrial and ventricular pacing energy control inputs determine the respective magnitudes of the pacing pulse energy so delivered . telemetry circuit 30 provides a bidirectional link between control block 39 of pacemaker 17 and an external device such as a programmer ( not shown ). it allows data such as the operating parameters to be read from or altered in the implanted module 10 . referring to fig1 , microprocessor 19 comprises two 16 - bit timers 51 and 52 , a cpu 53 , a vectored interrupt block 54 , a rom 55 , a ram 56 , an external memory 57 , a ports block 41 and an internal communication bus 40 . ram 56 acts as a scratch pad and active memory during execution of the various programs stored in rom 55 and used by microprocessor 19 . these programs include system supervisory programs and neuromuscular stimulation control programs , as well as storage programs for storing , in external memory 57 , data concerning the functioning of module 10 and the electrogram provided by ventricular cardiac lead 13 ( fig9 ). timers 5 1 and 52 , and associated control software , implement some timing functions required by microprocessor 19 without resort entirely to software , thus reducing computational loads on and power dissipation by cpu 53 . signals received from telemetry circuit 30 ( fig1 ) permit an external programmer ( not shown ) to change the operating parameters of pacemaker 17 by supplying appropriate signals to control block 39 . communication bus 42 serves to provide signals indicative of such control to microprocessor 19 . thus , it is also possible for an external programmer to control operation of the skeletal muscle stimulator 20 by means of signals provided to microprocessor 19 . appropriate telemetry commands may cause telemetry circuit 30 to transmit data to the external programmer . data stored is read out , by microprocessor 19 , on to communication bus 42 , through control block 39 in pacemaker 17 , and into telemetry circuit 30 for transmission to the external programmer by a transmitter ( not shown ) in telemetry circuit 30 . microprocessor 19 receives various status and / or control inputs from the pacemaker 17 , such as the sense signals on sense lines 45 and 49 . it performs operations , such as neuromuscular stimulation timing and amplitude control functions , and produces outputs , such as the atrial pace control on line 46 and the ventricular pace control on line 50 , which determine the type of pacing that is to take place . other control outputs generated by microprocessor 19 include the atrial and ventricular pacing energy controls on buses 44 and 48 , respectively , which determine the magnitude of the pulse energy , and the atrial and ventricular sensitivity controls on buses 43 and 47 , respectively , which determine the sensitivity settings of the sensing circuits . in addition , the microprocessor 19 controls all aspects of skeletal muscle stimulation , as will be described in detail below , by formulating control signals and transmitting these signals over the skeletal muscle stimulation control bus 22 to skeletal muscle stimulator 20 . the effectiveness of the cardiac assistance provided by neuromuscular stimulation of the skeletal muscle graft 9 ( fig9 ) may be measured by diagnostic tests , including electrocardiogram monitoring , two dimensional and doppler echocardiography , nuclear medicine multigated scan procedures employing radioisotopes such as technetium 99m , and measurements of oxygen uptake during exercise . as a health care practitioner performs one or more of these diagnostic tests , neuromuscular stimulation parameters may be altered via telemetry to achieve the highest degree of cardiac assistance . for example , during an early conditioning phase of the skeletal muscle graft 9 , low - amplitude stimulation pulses are applied infrequently and a steady stimulation of the different channels is employed to activate the skeletal muscle without generating large current flows in the muscle . later , as the muscle becomes conditioned , the stimulating procedure may be tested and varied to determine an optimum stimulation procedure , which depends on the relative location of the electrodes with respect to the muscle innervation . fig1 illustrates an example of a bioelectrical stimulating device 1 for performing both cardiac pacing and long - term stimulation of skeletal muscles for cardiac assistance using systolic augmentation , in accordance with one embodiment of the bioelectrical stimulating device of the present invention . a latissimus dorsi skeletal muscle graft 215 is positioned over the right ventricle 201 of a patient &# 39 ; s heart 200 . the longitudinal fibers of the latissimus dorsi graft 215 are oriented generally perpendicular to the longitudinal axes of the right ventricle 201 , left ventricle 202 and interventricular septum 203 of the heart . the skeletal muscle is positioned in this manner so that when it is stimulated , it compresses the ventricles , particularly the left ventricle 202 , and improves the force of right and left ventricular contraction . in a preferred configuration , the latissimus dorsi muscle graft 215 is wrapped around the heart 200 and fixedly attached to itself to form a cup - shaped &# 34 ; sling &# 34 ;, using running sutures 220 . alternatively , the latissimus dorsi muscle graft 215 may be attached to the heart 200 along the borders of the right ventricular free wall 204 using running sutures 221 . a ventricular cardiac lead 13 is implanted in the heart &# 39 ; s right ventricle 201 and the skeletal muscle lead 21 extends from the muscle stimulator 20 ( of fig9 ) to the latissimus dorsi muscle graft 215 . the negative polarity ( m -) skeletal muscle lead portion 21 - is preferentially placed near nerve branches in the vicinity of the neuromuscular junction within the latissimus dorsi muscle graft 215 and the positive polarity ( m +) skeletal muscle lead portion 21 + is implanted into the muscle a predetermined distance ( i . e ., 2 to 5 cm ) from the negative polarity lead portion to provide for depolarization of intact motor nerve fibers . placement of he electrodes in this manner lessens the possibility of nerve damage while increasing the selectivity of stimulation to particular muscle fibers . when an electrode of skeletal muscle lead 21 generates an electrical stimulation in the vicinity of a nerve fiber , it induces an electrical charge across the nerve membrane , causing an excess flow of ions through the membrane . at the site of a cathode electrode ( m -), the potential outside the membrane becomes negative with respect to the inside potential . a weak cathodic potential cannot excite the fiber , but if this potential is increased above threshold , the nerve is excited . a further increase in stimulation amplitude above the threshold level does not augment the activity of the nerve . in the heart , biological or artificial pacing stimulates electrical and mechanical activation , which proceeds in a continuous progression of excitation . in contrast , a contraction of skeletal muscle is modulated by the number of muscle fibers which are stimulated and the rate of stimulation . rapid , repetitive stimuli which are delivered too frequently for individual muscle fibers to completely relax , result in a mechanical summation of contractile force until fusion occurs , causing the muscle to generate a considerable force . a protocol for skeletal muscle electrostimulation commonly includes a progression from single stimulating impulses to a train of impulses at a predetermined rate e . g ., 30 hz ). this progression takes place over a period of days or weeks . these impulses or bursts are coordinated with cardiac cycle timing . fig1 is a depiction of the interface between a pair of fig1 type multi - electrode neuromuscular stimulating leads 21 , including a positive lead 21 + and a negative lead and 21 -, and a patient &# 39 ; s latissimus dorsi muscle 215 . different portions of the latissimus dorsi muscle 215 may be stimulated independently due to the capability for independent programming of stimulation timing , intensity and duration for the electrode pairs 112 + and 112 -, 114 + and 114 -, 116 + and 116 -, 118 + and 118 -, and 120 + and 120 -. these electrode pairs are surgically placed in close proximity to nerve fiber branches 216 , 217 , 218 , 219 and 222 , respectively , so that each electrode pair will predominantly stimulate the appropriate nerve branch . the nerve fibers may have variable excitation thresholds due to differences in distance from an electrode pair to the nerve or variability in fiber diameter . furthermore , variations in the muscle fibers which are innervated by a particular nerve fiber may produce differences in excitation threshold . accordingly , the stimulation timing , intensity and pulse duration may be individually programmed following the surgical operation to produce an appropriate contraction behavior . the contractile performance of the muscle can be inspected visually during the implantation operation or inspected by means of ultrasonic imaging afterwards . fig1 illustrates a spatial configuration between electrodes 116 + and 118 + of the multi - electrode stimulating lead of the present invention , and nerve fibers 218 and 219 in a latissimus dorsi muscle 215 . here , the conductive portions of two intramuscular electrodes are placed in the muscle body and an electrical potential is applied between positive and negative electrode pairs to stimulate the muscle . fig1 and 16 illustrate an example of an aortomyoplasty application of cardiac assistance . during systole , blood flows from the left ventricle to the aorta . at the end of systole , the aortic valve closes . to augment the flow of blood to the arteries , the latissimus dorsi muscle 215 is stimulated to contract and compress the aortic wall during diastole . as seen in fig1 , the latissimus dorsi muscle 215 is innervated by a number of nerve fiber branches , shown here as fiber branches 216 , 217 , 218 , 219 and 222 , which innervate different portions of the muscle . accordingly , during surgical implantation , electrode pairs 112 + and 112 -, 114 + and 114 -, 116 + and 116 -, 118 + and 118 -, and 120 + and 120 - are placed in the vicinity of the nerve fibers to stimulate muscle contraction in five segments . to ensure that blood will flow to the arteries , rather than backward to the heart , electrode pair 112 + and 112 - are stimulated first , followed sequentially by pairs 114 , 116 , 118 and 120 , with the synchronization delay gradually increasing for each subsequent pair as shown in fig1 . furthermore , the amplitude , or intensity , of stimulation is generally strongest for electrode pair 112 and gradually is diminished for each successive electrode pair 114 , 116 , 118 and 120 . note that the stimulus intensity may be further varied due to differences in stimulation threshold for a given nerve fiber . in a similar manner , fig1 and 18 illustrate an example of a cardiomyoplasty application of cardiac assistance . during systole , blood flows from the left ventricle to the aorta . to enhance the flow of blood to the arteries , the latissimus dorsi muscle 215 is stimulated to contract and compress the ventricle during systole . as seen in fig1 , the latissimus dorsi muscle 215 is innervated by a number of nerve fiber branches , shown here as fiber branches 216 , 217 , 218 , 219 and 222 , which innervate different portions of the muscle . accordingly , during surgical implantation , electrode pairs 112 + and 112 -, 114 + and 114 -, 116 + and 116 -, 118 + and 118 -, and 120 + and 120 - are placed in the vicinity of the nerve fibers to stimulate muscle contraction in five segments . to assist the flow of blood into the aorta , electrode pair 112 + and 112 - are stimulated first , followed sequentially by pairs 114 , 116 , 118 and 120 with the synchronization delay gradually increasing for each subsequent pair , as shown in fig1 . furthermore , the amplitude , or intensity , of stimulation is generally strongest for electrode pair 112 and gradually is diminished for each successive electrode pair 214 , 116 , 118 and 120 . again , the stimulus intensity may be further varied due to differences in stimulation threshold for a given nerve fiber . fig1 and 20 show an example of a skeletal muscle ventricle application of cardiac assistance . a skeletal muscle ventricle operates in a manner similar to an aortomyoplasty application , but rather than wrapping skeletal muscle around the aorta , the muscle is wrapped around a cone - shaped mandrel 246 of material such as teflon ®, made by e . i . du pont de nemours and company , 1007 market street , wilmington , del . 19898 ( us ). the mandrel 246 defines a cone - shaped cavity in the muscle wrap , which cavity is termed a &# 34 ; skeletal muscle ventricle &# 34 ; ( smv ) 240 . the mandrel 246 is surgically placed in the body for a predetermined time ( for example , four weeks ), after which time it is removed and the skeletal muscle may be stimulated to contract about the smv . the skeletal muscle ventricle 240 is surgically interconnected to the descending aorta 242 using a synthetic bifurcation graft 244 . the bifurcation graft 244 may be constructed from a material such as gore - tex ®, made by w . l . gore & amp ; associates , inc ., 551 paper mill road , p . o . box 9329 , newark , del . 19714 ( us ). during systole , blood flows from the left ventricle to the descending aorta 242 . at the end of systole , the aortic valve closes . to augment the flow of blood to the arteries , the latissimus dorsi muscle 215 is stimulated to contract and compress the skeletal muscle ventricle 240 during diastole . as seen in fig1 , the latissimus dorsi muscle 215 is innervated by a number of nerve fibers , shown here as fibers 216 , 217 , 218 , 219 and 222 , which innervate different portions of the muscle . accordingly , during surgical implantation , electrode pairs 112 + and 112 -, 114 + and 114 -, 116 + and 116 -, 118 + and 118 -, and 120 + and 120 - are placed in the vicinity of the respective nerve fibers 216 - 219 and 222 to stimulate muscle contraction in five segments . to assist blood flow to the arteries the skeletal muscle at the apex or tip 248 of the cone of skeletal muscle ventricle 240 is stimulated first , followed sequentially by muscle segments positioned between the apex 248 and the base of the cone . therefore , electrode pair 120 + and 120 - is stimulated first , followed sequentially by pairs 118 , 116 , 114 and 112 , with the synchronization delay gradually increasing for each subsequent pair , as shown in fig2 . furthermore , the intensity of stimulation is generally strongest for electrode pair 120 and gradually is diminished for each successive electrode pair . as is the case with other cardiac assistance stimulation , the stimulus intensity may be variable due to differences in stimulation threshold for a given nerve fiber . from the foregoing discussion , it is apparent that the present invention provides a neuromuscular stimulating lead and device for generating stimulating pulses on the lead , which accomplishes substantial improvement in the hemodynamics of a patient &# 39 ; s cardiovascular system and results in an augmented cardiac output and stroke volume . multiple stimulation channels and multiple electrode leads , which may be independently programmed in terms of stimulation intensity , timing and duration , produce this improvement by providing the capability of sequentially contracting a surgically implanted cardiac assistance skeletal muscle to pump blood in a desired direction . although the invention has been shown and described with reference to a particular embodiment , it is to be understood that these embodiments are merely illustrative of the application of the principles of the invention . numerous modifications may be made therein and other arrangements may be devised without departing from the true spirit and scope of the invention .
a neuromuscular stimulation apparatus and procedure , which employs multiple channels of stimulation for the purpose of supplying directional control of blood flow in addition to augmenting the force of contraction . the apparatus comprises multiple channel stimulation electrodes and a multiple channel cardiosynchronous stimulator to selectively stimulate various sections of the skeletal muscle . the amplitudes of the stimulation pulses and the time delay following a cardiac event may be selected for each channel to appropriately stimulate the muscle to control the order of contraction of particular muscle fibers and thereby to govern the direction of blood flow .