Abstract:
A medical device known as an implantable therapeutic substance delivery device is configured for implanting in humans to deliver a therapeutic substance such as pharmaceutical compositions, genetic materials, and biologics to treat a variety of medical conditions such as pain, spasticity, cancer, and many other conditions. The infusion device incorporates a stepper motor that controls the infusion flow rate during the service life of the device. The stepper motor is controlled by continuously varying electrical pulse parameters based on the continuously decreasing power source voltage during the service life of the substance delivery device. In particular the stepper motor electrical pulse parameters, especially duty cycle, are selected to efficiently compensate for decreasing battery voltage thereby optimizing the motor performance while maximizing the power source service life. The infusion device has a housing, a power source, a therapeutic substance reservoir, a therapeutic substance pump, and electronics. Many embodiments of the therapeutic substance delivery device with optimized pump motor drive and its methods of operation are possible.

Description:
RELATED APPLICATIONS  
       [0001]    This application is related to the following co-pending applications entitled “Implantable Therapeutic Substance Infusion Device With Motor Stall Detector” by inventors Seifert et al. (attorney docket number P8905.00) and “Implantable Therapeutic Substance Infusion Device With Active Longevity Projection” by inventors Rogers et al. Ser. No. 09/809,809 Filed Mar. 16, 2001 (attorney docket number P8904.00), which are not admitted as prior art with respect to the present invention by its mention in this cross reference section. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This disclosure relates to a medical device and more particularly to an implantable therapeutic substance infusion device, also known as an implantable drug pump, optimized peristaltic pump motor drive circuit.  
         BACKGROUND OF THE INVENTION  
         [0003]    The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Clinicians use medical devices alone or in combination with therapeutic substance therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. One type of medical device is an implantable therapeutic substance infusion device.  
           [0004]    An implantable therapeutic substance infusion device is implanted by a clinician into a patient at a location appropriate for the therapy. Typically, a therapeutic substance infusion catheter is connected to the device outlet and implanted to infuse the therapeutic substance such as a drug or infusate at a programmed infusion rate and predetermined location to treat a condition such as pain, spasticity, cancer, and other medical conditions. Many therapeutic substance infusion devices are configured so the device can be refilled with therapeutic substance through a septum while the device is implanted. Then the time the device can be implanted may not be limited by therapeutic substance stored capacity of the device. An example of an implantable therapeutic substance infusion is shown in Medtronic, Inc. product brochure entitled “SynchroMed® Infusion System” (1995).  
           [0005]    Electrically powered implanted therapeutic substance infusion devices consume energy delivered typically by a battery, also called a power source, and can require replacement once implanted due to depletion of the battery. Typically the most significant power-consuming component in an implantable infusion device is the therapeutic substance metering motor such as a stepper motor.  
           [0006]    A stepper motor is an electromechanical device whose rotor rotates a discrete angular amount when an electrical drive pulse is applied to the stator windings. The amplitude and the width of the electrical drive pulse must be tailored to the electromechanical properties of the motor in order to achieve rotation, stability, and optimal energy consumption. Examples of instability include the motor rotating backwards, stepping ahead then “flipping back” to its starting position, and not stepping at all. For a stepper motor to function normally and efficiently over a wide power source voltage range, the motor drive pulse needs to be adjusted proportional to the voltage change of the power source.  
           [0007]    If all motor drive pulse parameters are held constant while the power source voltage decreases, a decrease due to normal consumption of power source energy, excess energy above that needed by the motor is delivered at the beginning of the service life of the device. This occurs because the pulse parameters needed for the end of service life, for example, pulse width, are greater than needed at the beginning.  
           [0008]    Thus, unless the pulse parameters are appropriately varying as the power source voltage is varying, the excess energy drawn from the power source undesirably reduces the service life of the implantable pump. This may cause an early need to replace the pump which is undesirable.  
           [0009]    Since replacement of the implanted device requires an invasive procedure of explanting the existing device and implanting a new device, it is desirable to extend battery life to the greatest extent practicable. Some previous implantable infusion devices have reduced power consumption by varying the pulse width of the motor drive signal, but stepper motors can become unstable or stall under some circumstance when the pulse width is varied from the optimal pulse width that the motor is typically designed to use. An example of a motor drive signal with a varying pulse width is shown in Japanese Patent 11,042,286 “Intracorporealy Embedded Type Liquid Medicine Supplying Apparatus” by Yamazaki (Feb. 16, 1999).  
           [0010]    For the foregoing reasons, there is a need for an implantable therapeutic substance infusion device with optimized pump motor drive to increase the infusion device&#39;s effective service life. This increased service life reduces the overall cost of the medical therapy and the inconvenience to the patient and clinician for future device replacement surgeries.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    An implantable therapeutic substance infusion device embodiment with optimized peristaltic pump motor drive to maximize the service life of the power source while maintaining assurance that the energy needed to drive the pump motor is sufficient over the life of the power source and the life of the device. The slow continuous decrease of power source voltage versus time is periodically sampled and measured. A measurement circuit measures this voltage signal and this voltage value is used to continuously vary the motor drive parameters generated by the motor drive circuit to compensate for the decreasing voltage. The duty cycle of the short drive pulses increases as the power source voltage decreases thereby compensating for the reduced voltage drive amplitude to the motor. The electrical energy delivered by the motor drive circuit is substantially constant even when the power source voltage decreases. This invention avoids the waste of significant power source energy at the high initial power source voltage if the motor drive pulse width and repetition rate were constant over the service life of the pump and power source. The infusion device has a housing; a power source; a therapeutic substance reservoir configured for containing a therapeutic substance and being refilled with the therapeutic substance while implanted; a therapeutic substance pump fluidly coupled to the therapeutic substance reservoir, and electrically coupled to the power source; and, electronics electrically coupled to the power source and coupled to the therapeutic substance pump. The electronics include a processor; memory coupled to the processor; an infusion program residing in memory, the infusion program capable of being modified once the therapeutic substance infusion device is implanted; and, transceiver circuitry coupled to the processor for externally receiving and transmitting therapeutic substance infusion device information. Many embodiments of the therapeutic substance delivery device with optimized peristaltic pump motor drive and its methods of operation are possible. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 shows the environment of an implantable therapeutic substance infusion device embodiment;  
         [0013]    [0013]FIG. 2 shows an implantable therapeutic substance infusion device embodiment;  
         [0014]    [0014]FIG. 3 shows an implantable therapeutic substance infusion device with catheter embodiment;  
         [0015]    [0015]FIG. 4 shows an exploded view of an implantable therapeutic substance infusion device with peristaltic pump embodiment;  
         [0016]    [0016]FIG. 5 shows a block diagram of an implantable therapeutic substance infusion device embodiment;  
         [0017]    [0017]FIG. 6 shows flow diagram for the motor drive control embodiment;  
         [0018]    [0018]FIG. 7 shows a schematic diagram of stepper motor control system embodiment;  
         [0019]    [0019]FIG. 8 shows an electrical pulse diagram versus time for the chopper motor control embodiment;  
         [0020]    [0020]FIG. 9 shows a diagram of the power source voltage versus depth of discharge of the power source superimposed with drive pulse duty cycle embodiment;  
         [0021]    [0021]FIG. 10 shows the drive pulse duty cycle with varying duty cycles embodiment, and  
         [0022]    [0022]FIG. 11 shows that the motor drive pulse energy is substantial constant over the useful voltage range of the power source embodiment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 1 shows the environment of an implantable medical device known as an implantable therapeutic substance delivery device  30 , also known as a drug pump, having a peristaltic pump with optimized peristaltic pump motor drive embodiment. The therapeutic substance delivery device  30  operates to infuse a therapeutic substance  36  stored in therapeutic substance reservoir  44  at a programmed flow rate into a patient  38 . The therapeutic substance delivery device  30  can be used for a wide variety of therapies such as pain, spasticity, cancer, and many other medical conditions.  
         [0024]    The implantable therapeutic substance delivery device  30  is typically implanted by a surgeon in a sterile surgical procedure performed under local, regional, or general anesthesia Before implanting the therapeutic substance delivery device  30 , a catheter  32  is typically implanted with the distal end position at the desired therapeutic substance delivery site  34  and the proximal end tunneled to the location where the therapeutic substance delivery device  30  is to be implanted. The implantable therapeutic substance delivery device  30  is generally implanted subcutaneous about 2.5 cm (1.0 inch) beneath the skin where there is sufficient tissue to support the implanted system. Once the therapeutic substance delivery device  30  is implanted into the patient  38 , the incision can be sutured closed and the therapeutic substance delivery device  30  can begin operation.  
         [0025]    [0025]FIG. 2 shows an implantable therapeutic substance delivery device  30  with optimized pump motor drive embodiment with housing  41  and fill port septum  40 . FIG. 3 shows implantable therapeutic substance delivery device  30  connected to catheter  32  prior to implantation into a patient  38  by a surgeon.  
         [0026]    The therapeutic substance  36  in pump reservoir  44  inside the pump is a substance intended to have a therapeutic effect such as pharmaceutical compositions, genetic materials, biologics, and other substances. Pharmaceutical compositions are chemical formulations intended to have a therapeutic effect such as intrathecal antispasmodics, pain medications, chemotherapeutic agents, and the like. Pharmaceutical compositions are often configured to function in an implanted environment with characteristics such as stability at body temperature to retain therapeutic qualities, concentration to reduce the frequency of replenishment, and the like. Genetic materials are substances intended to have a direct or indirect genetic therapeutic effect such as genetic vectors, genetic regulator elements, genetic structural elements, DNA, and the like. Biologics are substances that are living matter or derived from living matter intended to have a therapeutic effect such as stem cells, platelets, hormones, biologically produced chemicals, and the like. Other substances are substances intended to have a therapeutic effect yet are not easily classified such as saline solution, fluoroscopy agents, and the like.  
         [0027]    The therapeutic substance  36  in reservoir  44  can be replenished in some embodiments of the implanted therapeutic substance delivery device  30  by inserting a non-coring needle connected to a syringe filled with therapeutic substance  36  through the patient&#39;s skin into a fill port septum  40  on the therapeutic substance delivery device  30  to fill the implanted device. The contents of the syringe are then injected into the pump reservoir  44 .  
         [0028]    If the therapeutic substance delivery device  30  requires replacement due to conditions such as power source depletion or other condition, an incision is made near the implanted therapeutic substance delivery device  30 , and the old therapeutic substance delivery device  30  is removed, also known as explanted. After the old therapeutic substance delivery device  30  has been explanted, typically a new therapeutic substance delivery device  30  is then implanted.  
         [0029]    [0029]FIG. 4 shows an exploded view of an implantable therapeutic substance infusion device with optimized pump motor drive comprised of a housing  41 , a power source  42 , a therapeutic substance reservoir  44 , a therapeutic substance pump  46 , and electronics  48 .  
         [0030]    The housing  41  is manufactured from a material that is biocompatible and hermetically sealed such as titanium, tantalum, stainless steel, plastic, ceramic, and the like. The power source  42  is carried in the housing  41 . The power source  42 , selected to operate the therapeutic substance pump  46  and electronics  48 , may be a lithium ion (Li+) battery, a capacitor, and the like.  
         [0031]    The therapeutic substance reservoir  44  is carried in the housing  41  and is configured to contain therapeutic substance  36 . The therapeutic substance pump assembly  46  is carried in the housing  41 , and is fluidly coupled to the therapeutic substance reservoir  44  and electrically coupled to the power source  42 . The therapeutic substance pump assembly  46  is a pump sufficient for infusing therapeutic substance  36  such as the peristaltic pump with stepper motor drive that can be found in the SynchroMed&amp; Infusion System available from Medtronic, Inc.  
         [0032]    A stepper motor is an electromechanical device whose rotor rotates a discrete angular amount when an electrical drive pulse is applied to the stator windings. The amplitude and the width of the pulse must be tailored to the electromechanical properties of the motor in order to achieve rotation, rotational stability, and optimal energy consumption. An example is a motor that rotates 180 degrees with the application of a 3 volt, 11.2 millisecond, square pulse. A second pulse is then applied at minus 3 volts to rotate an additional 180 degrees making a complete revolution.  
         [0033]    The stepper motor is mechanically coupled by gears to the peristaltic roller pump where the rollers rotate in such a way as to squeeze a compressible tube and drive liquid through the tube lumen in one direction. In effect the therapeutic substance  36  from the reservoir  44  flows in the tube and is metered to the patient  38  via catheter  32  to anatomical sight  34 .  
         [0034]    Examples of instability include the motor rotating backwards, stepping ahead then “flipping back” to its starting position, and not stepping at all. For a stepper motor to function normally and efficiently over a wide power source voltage range, the motor drive pulse parameters need to be adjusted proportional to the voltage change of the power source.  
         [0035]    [0035]FIG. 5 shows a block diagram device embodiment. The electronics  48  are carried in the housing  41  and coupled to the therapeutic substance pump  46  and the power source  42 . The electronics  48  include a processor, memory, an infusion program, and transceiver circuitry.  
         [0036]    At the processor can be a microprocessor, an application specific integrated circuit (ASIC) state machine, a gate array, a controller, and the like. The electronics  48  are configured to control the therapeutic substance pump  46  infusion rate and can be configured to operate many other features such as patient alarms and the like. The infusion program and other device parameters and patient information reside in memory and are capable of being modified once the therapeutic substance infusion device is implanted. The transceiver circuitry is coupled to the processor for externally receiving and transmitting therapeutic substance infusion device information.  
         [0037]    [0037]FIG. 6 shows a flow chart of a method for operating a therapeutic substance infusion device  30  with optimized pump motor drive. The method embodiment includes receiving an instruction to infuse a therapeutic substance  61 . Together with the elements of measuring, receiving and storing the power source voltage signal in  62 , the drive pulse duty cycle is calculated or provided by a look-up table in  63 . The drive pulse duty cycle is used for delivery of motor drive pulses  64  to the motor that generates the infusion of therapeutic substance from the pump  65 .  
         [0038]    [0038]FIG. 7 shows a schematic diagram of stepper motor control system to illustrate the components of the preferred embodiment. The stepper motor  106  is connected to the power source  102  via the motor drive circuit  105 , and mechanically coupled with gears  107  to the therapeutic substance infusion pump  108 . The motor drive circuit  105  is configured with a drive interval timing circuit  105 a and a drive pulse circuit  105 b. The drive interval timing circuit  105   a  specifies a substantially fixed drive interval for drive energy to be delivered to the motor  106  to operate a therapeutic substance pump  108  according to a therapy program. The drive pulse circuit  105   b  is coupled to the power source measurement circuit  140  to generate a predetermined number of drive pulses within the drive interval according to the power supply  102  voltage to reduce motor  106  energy consumption. The duty cycle of short drive pulses varies according to the power source voltage  95  of FIG. 9 at terminal  103  as measured by the power source measurement circuit  140  to reduce motor energy consumption.  
         [0039]    FIG. 8  shows the repetition rate of the long fixed drive period t2 varies dependent on the programmed pump flow rate in accordance with the therapy program. For example, the repetition rate is high for high therapy flow rates, and the repetition rate is low for low therapy flow rates.  
         [0040]    In FIG. 7  the power source voltage  95  at terminal  103  is feed to the quad switches  111 ,  112 ,  113 , and  114  as well the power source measurement circuit  140 . The power source measurement circuit  140  is composed of a standard analog-to-digital converter as well as other electrical components. The power source measurement circuit  140  generates a signal or digital word proportional to the power source voltage that is fed to the processing unit  141 . The processing unit  141  produces a duty cycle control signal or digital word that is fed to the controller  104  in the motor drive circuit  105 . The controller  104  in the motor drive circuit is composed of standard digital logic, registers and other logic components to configure the motor drive pulses. Registers may include but are not limited to a pulse interval register, a drive pulse width register, a drive pulse duty cycle register, and a drive pulse expiration register.  
         [0041]    The controller  104  outputs electrical pulses to drive the four motor drive switches  111 ,  112 ,  113 , and  114 . Outputs  116  and  118  of the quad switch assembly produce a motor drive pulse train that energizes the motor stator magnet  122 , in turn rotating the motor rotor  120 . The motor stator coil  124  is wound around the magnetic material stator  122 . The rotor  120  is mechanically coupled by gears  107  to the pump mechanism  108 . The rotor  120  of the stepper motor rotates in such a way as to propel and meter the therapeutic infusion substance  36  from the pump  30  to the patient  38 .  
         [0042]    This invention achieves motor drive energy optimization by dividing the usual long drive pulse into numerous shorter pulses. For example, the long single drive pulse can be performed by  23  shorter pulses applied over the time period t 2  in FIG. 8.. Due to the large inductance of the motor&#39;s stator winding  124 , the flow of current is not significantly disrupted at each short pulse. The duty cycle, ratio of “on time” to “total time”, of the short pulses is directly proportional to the energy savings compared to a 100% “on time” drive pulse. The duty cycle changes in small discrete increments over the usable power source voltage range such that the energy that drives the motor is substantially constant and of proper amplitude for stable motor function. For example, the duty cycle increases in  1 / 16  steps as the power source voltage decreases and vice versa.  
         [0043]    [0043]FIG. 8 illustrates how the stepper motor pulse duty cycle is achieved. The long pulse t2 is combined or commutated with chopper oscillator pulses  80  from chopper oscillator  110  in the controller  104  of the motor drive circuit  105 . The long motor drive pulse width t2 is fixed at 11.2 milliseconds. The  2048  hertz chopper oscillator  110  provides square wave pulses  80  that are used to achieve the short drive pulse t5. The duty cycle of the 2048 hertz pulses t5 in periods t2 and t4 are dependent on the power source voltage as described above. The predetermined number of short drive pulses t5 are about 23 pulses within the substantially fixed drive interval of 11.2 milliseconds of t2 and t4. The drive periods t2 and t4 have a duty cycle in the range from about 75% to about 100%. This combination of varying short pulse parameters achieves substantially constant motor drive energy to reliably operate a therapeutic substance pump according to a therapy program.  
         [0044]    [0044]FIG. 9 illustrates the continuously varying power source voltage  95  versus the Depth of Power Source Discharge during the service life of the infusion device. Superimposed on FIG. 9 is the motor drive short pulse duty cycle  91  expressed in percent. As the power source voltage decreases, the duty cycle increases, ranging from 75% to 100%. The end of service life  92  of the power source  42  is where 100% duty cycle occurs. Until the end of service life is reached, the duty cycle of the stepper motor varies to compensate for the decreasing power source voltage.  
         [0045]    [0045]FIG. 10 illustrates the duty cycle, defined as t5 divided by t6, as it varies depending on power source voltage  95 . At 100% duty cycle, the short drive pulses t5 are on during the entire 11.2 millisecond drive period t2 in FIG. 8. At 75% duty cycle, the long drive pulse is composed of 23 consecutive short drive pulses each at about 0.75/2048 hertz=0.366 milliseconds long.  
         [0046]    [0046]FIG. 11 illustrates the long pulse motor drive energy  1100  is substantially constant versus power source voltage. This near constant delivered energy assures stable and reliable motor  120  rotation even when the power source voltage  95  decreases.  
         [0047]    Many other related functions could be derived from this optimized motor drive invention. For example, if a motor stall is detected, the drive pulse duty cycle could be increased or decreased to overcome the motor stall or to do diagnostics of the stall. An intermittent motor stall might occur due to significant environmental magnetic field interactions such as experienced with magnetic resonance imaging technology.  
         [0048]    In addition, if a very large change of power source current is needed, the resultant anticipated power source voltage reduction could be predicted using a power source forecast circuit. The power source forecast circuit identifies that the power source voltage will change abruptly and that the duty cycle must be adjusted. Typically the duty cycle is increased in anticipation of lower power source voltage. Such a dynamic prediction may be needed because of inherent time delays of the power source measuring or processing system. Large power source current changes might occur when the pump infusion rate is abruptly changed from a very low rate to a very high rate or an alarm is activated.  
         [0049]    Thus, the implantable therapeutic substance infusion device  30  embodiments with optimized pump motor drive achieves the maximum service life of the power source while maintaining assurance that the stepper motor will function normally over the entire range of power source voltages. An energy efficient motor drive is achieved based on measuring power source voltage and continuously controlling the motor drive pulse parameters to minimize the electrical energy delivered to the pump motor. A predetermined number of drive pulses is selected to operate the stepper motor while substantially maintaining motor stability and avoid motor stall.  
         [0050]    Thus, embodiments of the implantable infusion device with optimized peristaltic pump motor drive are disclosed to increase the infusion devices effective service life. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.