US 20070232858 A1
A steerable shaft of a medical instrument is steered by one or more control cables. The control cables are in contact with a steering system tension control device that reduces the tension in the control cables caused by bends in the shaft.
1. A steering system tension control device for a medical instrument having a shaft, comprising:
(a) a control cable disposed within the shaft of the medical instrument that is selectively tensioned to steer a tip of the medical instrument, the control cable having a core wire surrounded by an outer sheath; and
(b) a spring disposed to relieve tension in the control cable at a predetermined tension threshold caused by bends in the shaft.
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13. A medical instrument having a steerable shaft, comprising:
(a) a shaft having a distal end and a proximal end;
(b) a handle connected to the proximal end of the shaft;
(c) a control cable having an outer sheath and a core wire that is connected to or adjacent a distal location of the shaft such that the distal end of the shaft is oriented in a desired direction by tensioning the core wire of the control cable; and
(d) a spring positioned to relieve the tension of the control cable by being compressed by the tension created in the cable as the shaft of the medical instrument is bent.
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24. A steering system tension control device for a medical instrument having a shaft and a control cable disposed within the shaft, wherein the control cable includes a core wire surrounded by an outer sheath, comprising a spring disposed to compress by the action of the outer sheath caused by bends in the control cable.
25. The steering system tension control device of
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27. A medical instrument having a steerable shaft, comprising:
(a) a control cable having a core wire and an outer sheath surrounding the core wire;
(b) a spring disposed to relieve tension in the control cable by compressing at a predetermined tension threshold caused by bends in the shaft.
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The present invention relates to medical instruments in general, and to instruments with steerable shafts in particular.
As an alternative to performing more invasive medical procedures, many physicians are utilizing endoscopes and catheters to perform diagnostic and therapeutic procedures on the internal tissues of patients. With this less invasive approach, a medical instrument, such as an endoscope or a catheter is advanced to a site of interest in order to perform the indicated procedure. Most endoscopes and catheters have a flexible shaft that allows the endoscope or catheter to wind its way through bends in the patient's anatomy until it reaches the tissue of interest. In order to advance the flexible shaft, most steerable endoscopes have a system of control cables that act in pairs to help direct the distal tip of the shaft. Each control cable is disposed opposite to its pair, and the control cables move in opposition to one another such that as one control cable is being pulled, the other is being released. The effect is to bend the tip of the shaft in a desired direction. In many endoscopes or catheters, the control cables have an outer sheath and an inner core wire. The outer sheath acts to transmit the longitudinal motion of the core wire to the distal tip of the endoscope. During a medical procedure, it is not uncommon for the shaft to form one or more loops as it is navigated to the tissue of interest. When a shaft including a control cable is looped, the outer sheath becomes increasingly stiff and harder to navigate within the body. At every bend of the shaft, the distances traveled by the core wire and its respective outer sheath differ, producing tension in the outer sheath and/or the core wire and increasing the amount of force needed to exert longitudinal force in the pull wire. This results in the user having less control over the tip of the device and less ability to detect external forces acting on the tip. Therefore, there is a need for a navigation system for use in steerable medical instruments that is still steerable at low forces if looped in the body.
The present invention is an elongated medical instrument including a shaft that is steerable in a desired direction. Control cables in the shaft include an outer sheath and an inner core wire that is tensioned to articulate the distal tip of the shaft. To address the problems described above, the ends of the control cable are in contact with a steering system tension control device so that tension in the control cable created as a result of loops or bends in the shaft is relieved.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
As indicated above, the present invention is a device for relieving tension that occurs in control cables of steerable medical instruments as a result of loops and bends in the instrument. Although the disclosed embodiments are shown for use in an endoscope, it will be appreciated that the invention may be used in any steerable medical instrument, such as catheters for vascular, urological, and laparoscopic applications or the like.
The core wires 104 a and 104 b extend from the distal tip 112 of the shaft 108 to a spool 114 within the interior and at the proximal end of the handle 116. The spool 114 is connected to a rotatable knob dial 118 that is exterior to the handle 116. The dial 118 can be turned clockwise or counterclockwise to rotate the spool 114. The distal ends of the core wires 106 a and 106 b are secured to the distal tip 112 of the shaft 108. The proximal ends of the core wires 106 a and 106 b are connected to the spool 114. For example, the core wires 106 a and 106 b may be connected at opposite tangents on the spool 114. Alternatively, the core wires 106 a and 106 b can be looped one or more times around the spool 114. In one embodiment, the core wires 106 a and 106 b can be the halves of a unitary core wire that loops around the spool 114. In yet another embodiment, the core wires 106 a and 106 b are distinct control cables that are separately attached to the spool 114. The core wires 106 a and 106 b can be attached to the distal tip 112 and to the spool 114 via an enlarged head or a barrel-like member, similar to a bicycle brake cable, that is inserted within a mating slot that enables the core wires to be removed. The core wires 106 a and 106 b are free to slide within the respective outer sheaths 104 a and 104 b according to the rotation of the dial 118 and the spool 114. The rotation of the dial 118 and spool 114 results in one or more of the core wires being tensioned. For example, in
In order to relieve tension in the cables, one embodiment of the invention includes a steering system tension control device 120. As best seen in
A compression spring 128 is placed in contact with the slide block 122 on the opposite side to the outer sheaths 104 a and 104 b. The opposite end of the spring 128 rests against an immovable abutment 129. Alternatively, the spring 128 can be connected to a roller (cam follower) which is in contact with a cam surface as further described below. When one or both outer sheaths 104 a and 104 b are under compression (due to looping or significant bending of the shaft) sufficient to overcome the counteracting force of the spring 128, the slide block 122 will give and slide to compress the spring 128. Such action relieves the compression on one or both of the outer sheaths 104 a and 104 b, relieving the tension on the core wires 106 a and 106 b and making them easier to move. The tension in the core wires 106 a and 106 b is not allowed to exceed a predetermined limit that is set by the counteracting force of spring 128. The spring 128 stiffness is selected so that it can withstand (without compression) the tension applied to the core wires 106 a and 106 b by the user during regular steering to bend the tip (especially at low looping configurations), but will compress when, for example, four cables are looped, or significantly bent, to relieve the tension.
The slide block 122 and the surfaces of the walls against which the slide block 122 slides can be made from, or covered with, a naturally lubricious material, such as a polyfluoro-carbon polymer, such as polytetrafluoroethylene (TEFLON®) or a polyamide to reduce the friction between the slide block 122 and the sliding surfaces.
While the steering system tension control device 120 is illustrated as being located in the handle 116 of the endoscope and has a spring 128 to act against the proximal ends of the outer sheaths 104 a and 104 b, an alternative embodiment can have one or more springs that act against the distal ends of the outer sheaths 104 a and 104 b at the distal end of the shaft. The spring stiffness is designed to compress during shaft looping or bending and relieve tension in the core wires 106 a and 106 b. Furthermore, the outer sheaths 104 a and 104 b can be divided into two or more sections from the distal location to the proximal location. One or more springs can be disposed in the “breaks” between sections of the outer sheaths. In such configurations, each section of the outer sheath has intermediate ends against which a spring can be disposed to act against and between two sections of the same control cable. Several springs, therefore, can be disposed on a single control cable. Furthermore, a helical spring is a representative spring. Alternative springs include leaf springs, elastomer materials, gas or fluid-filled chambers with pistons, compressed air chambers, or the like having characteristic spring-like behavior.
Although the embodiment shown in
In another embodiment, the outer sheath can be made from a tightly wound coil material. Therefore, one inexpensive method of placing springs in one or various sections of the sheath is to wind a coil with variable pitch at locations in the coil that can be used for the sheath and the spring or springs by separating the loops of the coil. For example, the windings of the outer sheath may be spread apart to form a compressible spring that compresses under the force built up as the outer sheath is lodged within the body. In this embodiment, the windings of the outer sheath also act as springs in addition to or as an alternative to the slide block and spring configuration.
It is also appreciated that the spring is acting as a compressible member. A less expensive version of the design involves a compressible block made of polypropylene, or similar material, in the handle of the device to anchor the outer sheaths. The thickness of the block and the durometer of the material can be adjusted to give the required elastic compression/deflection to relieve tension on the control cables during looping or significant bending of the shaft.
Another embodiment of this design has the sliding block that anchors the outer sheaths connected directly to the cam without a spring. By rotating a lever on the outside of the handle, the physician can control the location of the block and, hence, the tension in the steering cables.
The stiffness of a spring of any outer sheath or core wire of the embodiments described above can be calculated through designs of experiments by conducting testing at low and high looping configurations. To gauge a suitable spring stiffness, the following general guidelines are provided.
About 20° of play on the dial 118 appears to be the limit that is acceptable to most physicians. A suitable shaft has very little, if any, looseness in the control cables at low looping configurations and prevents tension from building up to ensure low steering torques at high looping configurations (2¼to 3 loops, where each loop is 360° ). A suitable compression spring is designed to compress and compensate for the increase in length of the outer sheath as more bends are made in the shaft to substantially keep the core wire path length constant. During low looping configurations, the compression spring is stiff enough to withstand the articulation forces transmitted through the steering dial(s). One optimum spring stiffness appears to be in the range of about 60 lbs./in. to about 100 lbs./in. It can be appreciated that the optimum spring stiffness can depend on many factors, such as, the bending stiffness of the tip, the stiffness of the outer sheath and core wire combined, and the number of loops expected during a procedure.
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the scope of the invention. Therefore, the present invention is to be determined from the following claims and equivalents thereof.