Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-10-28
2001-06-19
Yasko, John D. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S151000, C128SDIG001
Reexamination Certificate
active
06248093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to improvements in infusion pumps such as those used for controlled delivery of medication to a patient. More specifically, this invention relates to an improved infusion pump having a modified and space-efficient drive system.
2. Description of the Related Art
Infusion pump devices and systems are relatively well-known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact pump housing adapted to receive a. syringe or reservoir carrying a prescribed medication for administration to the patient through infusion tubing and an associated catheter or infusion set.
The infusion pump includes a small drive motor connected via a lead screw assembly for motor-driven advancement of a reservoir piston to administer the medication to the user. Programmable controls can operate the drive motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period of time. Such infusion pumps are utilized to administer insulin and other medications, with exemplary pump constructions being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653 and 5,097,122, which are incorporated by reference herein.
Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication or other fluids over an extended period of time. The infusion pump can be designed to be extremely compact as well as water resistant, and may thus be adapted to be carried by the user, for example, by means of a belt clip or the like. As a result, important medication can be delivered to the user with precision and in an automated manner, without significant restriction on the user's mobility or life-style, including in some cases the ability to participate in water sports.
These pumps often incorporate a drive system which uses a lead screw coupled to motors. The motors can be of the DC, stepper or solenoid varieties. These drive systems provide an axial displacement of the syringe or reservoir piston thereby dispensing the medication to the user. Powered drive systems are advantageous since they can be electronically controlled to deliver a predetermined amount of medication by means well known in the art.
In the operation of these pump systems, the reservoir piston will be fully advanced when vitually all of the fluid in the reservoir has been dispensed. Correspondingly, the axial displacement of the motor lead screw is also typically fully displaced. In order to insert a new reservoir which is full of fluid, it is necessary to restore the lead screw to its original position. Thus the lead screw will have to be rewound or reset.
DC motors and stepper motors are advantageous over solenoid motors in that the former are typically easier to operate at speeds that allow rewinding the drive system electronically. Solenoid based drive systems, on the other hand, often must be reset manually, which in turn makes water resistant construction of the pump housing more difficult.
Lead screw drive systems commonly use several gears which are external to the motor.
FIG. 1
shows such a lead screw arrangement which is known in the art. A motor
101
drives a lead screw
102
which has threads which are engaged with a drive nut
103
. Thus the rotational force of the lead screw
102
is transferred to the drive nut
103
which causes it to move in an axial direction d. Because the drive nut
103
is fixably attached to a reservoir piston
104
, it likewise will be forced in an axial direction d′, parallel to direction d, thus dispensing the fluid from the reservoir
105
into the infusion set
106
. The entire assembly can be contained in a water resistant housing
107
.
FIG. 2
shows a different lead screw arrangement which also is known in the art. In this arrangement, a motor
201
(or a motor with an attached gear box) has a drive shaft
201
a
which drives a set of gears
202
. The torque is then transferred from the gears
202
to a lead screw
203
. The threads of the lead screw
203
are engaged with threads [not shown] in a plunger slide
204
. Thus the torque of the lead screw
203
is transferred to the slide
204
which causes it to move in an axial direction d′, parallel to the drive shaft
201
a
of the motor
201
. The slide
204
is in contact with a reservoir piston
205
which likewise will be forced to travel in the axial direction d′ thus dispensing fluid from the reservoir
206
into the infusion set
207
. The assembly can be contained in a water resistant housing
208
.
As previously noted, these lead screw drive systems use gears which are external to the motor. The gears are in combination with a lead screw with external threads which is used to drive the reservoir's piston. This external arrangement occupies a substantial volume which can increase the overall size of the pump. Moreover, as the number of drive components, such as gears and lead screw, increases, the torque required to overcome inherent mechanical inefficiencies can also increase. As a result, a motor having sufficient torque also often has a consequent demand for increased electrical power.
Yet another known drive is depicted in
FIGS. 3
a
and
3
b.
A reservoir
301
fits into the unit's housing
302
. Also shown are the piston member
303
which is comprised of an elongated member with a substantially circular piston head
304
for displacing the fluid in the reservoir
301
when driven by the rotating drive screw
305
on the shaft (not visible) of the drive motor
306
.
As is more clearly shown in
FIG. 3
b,
the reservoir
301
, piston head
304
and piston member
303
comprise an integrated unit which is placed into the housing
302
(
FIG. 3
a
).
The circular piston head
304
displaces fluid in the reservoir upon axial motion of the piston member
303
. The rearward portion of the piston member
303
is shaped like a longitudinal segment of a cylinder as shown in
FIG. 3
b
and is internally threaded so that it may be inserted into a position of engagement with the drive screw
305
. The drive screw
305
is a threaded screw gear of a diameter to mesh with the internal threads of the piston member
303
. Thus the motor
306
rotates the drive screw
305
which engages the threads of the piston member
303
to displace the piston head
304
in an axial direction d.
While the in-line drive system of
FIG. 3
a
achieves a more compact physical pump size, there are problems associated with the design. The reservoir, piston head and threaded piston member constitute an integrated unit. Thus when the medication is depleted, the unit must be replaced. This results in a relatively expensive disposable item due to the number of components which go into its construction.
Moreover the design of
FIG. 3
a
is not water resistant. Because the reservoir, piston head and threaded piston member are removable, the drive screw
305
and motor
306
are exposed to the atmosphere. Any water which might come in contact with the drive screw
305
and motor
306
will result in corrosion and probable motor failure.
The design of
FIG. 3
a
further gives rise to problems associated with position detection of the piston head
304
. The piston member
303
can be decoupled from the drive screw
305
. However, when another reservoir assembly is inserted, it is not known by the system whether the piston head
304
is in the fully retracted position or in some intermediate position. Complications therefore are presented with respect to providing an ability to electronically detect the position of the piston head
304
in order to determine the extent to which the medication in reservoir
301
has been depleted.
The construction of pumps to be water resistant give rise to operational problems. As the user travels from various elevations, such as might occur whe
MiniMed Inc.
MiniMed Inc.
Yasko John D.
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