Powered Capillary Array Pump and Controller

Publication Summary

Current implantable pumps are offered in two basic configurations: electronically adjustable, battery-operated pumping systems and fixed-rate, passive pumping systems. Electronically adjustable systems offer physicians the ability to change medication dosages to match the patient's needs including the periodic administration of bolus doses. The disadvantage of electronically operated pumps is that, at least currently, they must be surgically replaced every few years due to exhaustion of the battery. Fixed-rate, passive pumps offer physicians and patients a long system life since no battery is generally required. Among the passive system's drawbacks are that no adjustment can be made to the medication rate without emptying and then refilling the pump; and that no telemetry exists to verify the pump status and patient identity. Passive pumps cannot currently compensate fully for changes in delivery due to altitude changes, changes in dosage between refills, nor do they currently have a means for the delivery of boluses from the reservoir. Both electronically adjustable and passive implantable pump systems are currently capable of delivering only one medication from a single reservoir into a single catheter. It would be advantageous to combine the best features of both systems into one implant, namely the ability to adjust flow rate as prescribed between changes in the delivery rate without the use of the battery power. This combination would allow for smaller implant size with still providing for extended battery life. It would be a further advantage to provide a method for the patient to deliver boluses of medication when experiencing breakthrough pain and to provide for the administration of more than one medication from separate reservoirs into separate catheters. The combined system described can be achieved by a passive (capillary flow) pump with internally controlled actuators and an external controller for programming. The external controller may query the pump for a complete record of the duration of each flow rate, times of adjustments, and dates and times of bolus administration. The adjustment of flow rate within the pump may be accomplished through the use of electrically activated latches and an adjustable-rate, constant-flow capillary array. The latches may be located internally near the rim of the device and may be actuated in sequence to form an indexing drive rotary actuator. The latches may be activated piezoelectrically, electromagnetically, or by electrical heating of a thermally activated latch. The rotary actuator plate is the control valve for an adjustable-rate, constant-flow, positive-pressure capillary pump. The entire pump may be fabricated from non-metallic materials with the exception of the latches, the circuitry, and the RF antenna. The reservoir may be fabricated from an elastomer such as silicone, urethane, or other implantable rubber compounds. The reservoir may alternatively be fabricated from low permeability plastics such that a liquid/gas phase or spring actuated pressurization chamber is created. The rotary actuator plate, port housing, top, middle, and bottom plates may be fabricated from polycarbonate, polysulfone, PEEK, or similar engineering plastics. The variable capillary channels may be a micro-molded feature inside of, or laminated to, the rotary actuator plate. The capillaries may be of different sizes for selection with the control valve; of the same size and "daisy chained" in series for control valve selection of the length; or a combination of the two. Laser machining of the micro-features is a suitable alternative to molding. The inlet port septum may be silicone rubber in the traditional fashion with a needle stop fabricated from an engineering plastic. A sintered polymer filter may be used to prevent particulates from obstructing the pump's capillary channels or the catheter(s). An additional polymer filter may be used on the outlet tube to prevent particulates from entering the pump when sampling fluids from a catheter through the pump. To protect against over-pressurization, a fluid-filled bellows valve may be used. This valve may be used to shut off the inlet whenever pressures greater than a predetermined threshold are reached. This may be an absolute-pressure-referenced shut off valve. The bellows may be partially filled with a liquid having a known vapor pressure threshold. When external pressure on the bellows exceeds the gas-to-liquid transition point of the internal vapor, the bellows contracts, closing the valve. This configuration would protect against over-pressurization of any reservoir selected for filling, as well as providing protection against over-pressurization during catheter access procedures utilizing the inlet port. The rotary actuator plate rests around and compresses the rotary seal. The rotary seal may be fabricated from a fluorosilicone compound for greatest life. In some embodiments, the actuator plate applies radial compression to the rotary seal, providing a tight seal around the entire inner circumference of the actuator plate. This rotary seal and the channels drilled through it provide for the selection of the desired capillary flow path. The rotary seal may contain more than one rotary actuator plate. The rotary seal channels can also provide for bypassing of the capillary channels to access the catheter directly; bypassing of the capillary channels to directly access any contained reservoir exclusively; to deliver a bolus of medication; to provide independent sensing of inlet, outlet, or reservoir pressure; and/or to provide independent capillary-flow-rate adjustments for multiple reservoirs. Similar functionality can also be achieved with seals on the faces of the actuator plate, though with greater design complexity. When making a flow rate change, the internal controller may power-up the implant's latches and change the valve settings. Once the actuator plate is moved to a new position it remains locked there until changed. The position of the actuator plate determines the starting and ending position of the reservoir channel and outlet channel of the rotary seal along the length of the capillary column contained within the actuator plate. This column may vary in cross-sectional area and/or length as it winds around the disc circumference, providing variable flow rates. Since the reservoir is pressurized, it is only necessary to select the desired section of the capillary column to vary the administration rate. In some implementations, the outer rim of the actuator plate interfaces with four thermally activated spring latches. The actuator plate rim may consist of a gear-tooth profile having a series of peaks and valleys. One of the latches may normally be closed, locking the plate in place. A second latch may be located such that, when actuated, it rotates the disc in a clockwise direction. A third latch may be located such that, when actuated, it rotates the disc in a counterclockwise direction. Rotary motion may be accomplished by activating one of the two rotational driving latches while simultaneously releasing the locking latch. The locking latch is then re-engaged after the plate has been moved to the next valley segment, completing one step in the rotation. The tips of the rotational latches may be slanted to engage the corresponding gear surface when extending, yet slide back over the precedent gear when retracting. The locking latch may have a symmetrical clip to center the gear tooth it locks to, completing the rotational step. The thermal constants of the latches may be minimized to provide a reasonable cycle time for each step, such as less than 2 seconds. A fourth (safety) latch may normally be open, where the others are normally closed. This latch can ensure that the actuator plate does not move if all of the latches are activated accidentally by a strong external field (MRI, RF, diathermy, etc.) or by overheating of the patient such as in a hot tub or sauna. Piezoelectric latches may offer a superior implementation. For both single and multiple disc configurations, spacers or standoffs may be used to stabilize the discs against excessive movement caused by vibration or other accelerations. An unlimited number of capillary array configurations are possible depending on the number of disc layers and the desired delivery options. The described elements may be used independently or in various combinations. For instance, the capillary array disc may be used for reservoir selection within a conventional implantable solenoid or peristaltic driven pump, the thermal actuators may be used with other types of implanted valves or pumps, and the like.

Country	United States
Language	English (United States)

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