Abstract:
An apparatus provides feedback regarding the material in which tip of the apparatus is located as the tip is advance into matter of varying resistances. The apparatus responds to a change in pressure, force, or other parameter such that when the tip reaches matter of a certain resistance, a change in the parameter is sensed. The apparatus provides a driving force to a penetrating medical device, such as a needle, when the apparatus tip encounters material of high resistance. When the apparatus tip encounters a low resistance material, no further driving force is applied to the apparatus. An inner core may be advanced into the low resistance material for deployment of a gas or a liquid as desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage filing under 35 U.S.C. § 371 of international application PCT/US2008/001622, filed Feb. 7, 2008, which claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application serial number 60/899,920, filed Feb. 7, 2007. 
     FIELD 
     The inventions disclosed herein relate generally to penetrating medical devices, and more particularly to penetrating medical devices, such as needles, that are to be placed into specific tissues or regions of various tissues or tissue compartments. 
     STATEMENT REGARDING FEDERALLY FUNDED RESEARCH 
     No federal funds were used in the development of the invention. 
     DISCUSSION OF RELATED ART 
     Various medical procedures employ the placement of needles or other penetrating medical devices within the body. Because direct visual observation of the position of the devices within the body is not possible in many procedures, placement of the devices can be challenging. Examples of medical procedures in which placement of the tip of a penetrating device is important include: 
     Arterial Cannulation 
     Arterial Cannulation (A-lines) is a common procedure in surgery and intensive care to allow arterial pressure monitoring, repeated blood gas sampling, and access to blood for other quantitative assays. Typically, A-lines are inserted in the radial artery of the wrist, but also may be inserted into the axillary artery in the underarm, the femoral artery in the groin, and the pedal artery in the foot. Over eight million A-lines are placed each year in the USA and over 2.5 million are placed in Europe each year. Recently, a 2004 guest editorial in the Journal of Critical Care commented that “even such a frequently used and seemingly benign procedure as cannulation of the radial artery can result in serious complications. The possibility of complications is especially high in critically ill patients who have other co-morbid conditions.” Significant complications such as arterial thrombosis, infection, hematoma, nerve injury, and ischemia leading to necrosis of tissues are estimated to range from 15% to 40% and the risk increases with multiple puncture attempts which are often required. In fact, approximately 20% of procedures result in temporary occlusion of the artery requiring an additional puncture event. The increase in risk with multiple punctures is due to direct trauma and increased risk of vasospasm. Multiple punctures also increase the time of the procedure which is typically performed under emergent conditions and thus can compromise stability and life of the patient. Additional attempts typically may be required in as many as 65% of procedures. Inability on the part of the clinician to pass the wire or catheter through the artery is one of the most common difficulties in catheterization. This can occur despite the return of pulsatile blood due to the angle of the needle in relation to the vessel. That is, the angle may be too acute or because the tip is not completely placed within the artery. 
     Central Venous Catheterization 
     Central venous catheterization (CVC), or central line placement, involves the cannulation of a vein with a relatively large bore catheter. Central lines are inserted into patients needing access for large amount of fluid administration; those needing monitoring of the central venous pressure; or patients on long-term intravenous therapies for administration of nutrition or medications (i.e., fluids, blood and derivatives, drugs, parenteral nutrition). The most common sites of insertion are the internal jugular vein (neck), subclavian vein (chest), or femoral vein (groin). Central line placement is generally performed by identifying external anatomical landmarks. However, typical anatomical variation of veins is approximately 8% and can be as high as 36% in cancer patients which can complicate CVC. Furthermore, the complication rate may correlate with the physician&#39;s level of experience. Therefore, it is not surprising that this procedure is associated with complications such as pneumothorax, inadvertent arterial central line placement, nerve injury, and hematoma in reportedly 14% of patients during emergent procedures. 
     Aside from requiring multiple needle insertions, occasionally arteries are incorrectly identified as veins and this misidentification is associated with a high incidence of related complications. Specifically, inadvertent placement of a central line into an artery instead of a vein is a prominent cause of morbidity and mortality and may occur in as many as 4.2% of cannulation procedures. 
       FIG. 1  shows a central line catheter  100  being tunneled under the skin and advanced through the subclavian vein  102  into the right side of the heart. 
     Epidural Placement 
     The current state of the art in epidural anesthesia involves the use of an epidural needle (such as a typical Tuohy needle  200 ) containing a stylet  202  with a blunt end  204 , as shown in  FIG. 2 . The operator performs a blind pass of needle  200  through several tissue layers listed here in order of penetration, some of which are shown in  FIG. 3 : 1) skin  206 , 2) subcutaneous tissue (not shown), 3) supraspinous ligament (not shown), 4) intraspinous ligament  212 , and 5) ligamentum flavum  214  to enter the epidural space  215 . 
     Tuohy needle  200  includes a hollow needle that is slightly curved at the distal end  220 . During epidural placement, stylet  202 , which includes a solid rod with a blunt end, is inserted into the Tuohy needle to prevent tissue from clogging the barrel of the needle. After the needle reaches the epidural space, the stylet is removed and a catheter  222  is inserted into the epidural space via the epidural needle. The curved end of the needle ensures that they catheter is inserted superiorly to the needle within the epidural space. The properly positioned catheter is connected to a syringe  224  for injection of anesthetic agent. 
     To guide proper placement, the operator uses anatomical landmarks identified by palpation together with changes in the force required to insert the needle through various layers of tissue. Consequently, successful epidural catheter placement requires a high degree of clinical skill on the part of the operator. To ensure proper placement of the needle tip, the operator delicately navigates the needle through the local anatomy, and substantially relies on manual haptic feedback to avoid puncturing the dura  216  and the spinal cord  218  which lies deep to the dura  216 . Extreme caution is therefore exercised in the positioning of the needle tip within the narrow epidural space (see epidural space  215  in  FIG. 3 ). To complicate matters, the epidural space has an irregular configuration and therefore the depth of needle penetration depends on the needle trajectory. In addition, during pregnancy and in morbidly obese patients, the anatomical landmarks are typically largely obscured. Attempts to correlate skin-to-epidural space distance with patient variables such as body-to-mass index have not proven useful and thus identification of the epidural space remains a technically demanding procedure, especially given that the skin-to-epidural space distance varies between 20-90 mm. If the needle is inserted too far resulting in the puncture of the dura matter and reaching the subarachnoid space, which occurs in approximately 3% of placement attempts (representing an incidence of 72,000 per year in the U.S. alone), a loss of cerebrospinal fluid (CSF) may ensue leading to disabling complications such as Post-dural Puncture Headache (PDPH) in 50% of these patients. If this misplacement is undetected and the falsely placed epidural catheter is utilized, the anesthesia in the subarachnoid space may reach high enough levels to cause spinal blockade and/or severe motor blockade, which may ultimately result in a rare but devastating complication of respiratory arrest hemodynamic shock. 
     SUMMARY OF THE INVENTION 
     Various embodiments disclosed herein may be used for one or more types of medical procedures, including, but not limited to: arterial cannulation; central venous catheterization; general catheter placement; administration of epidurals; placement of chest tubes; peritoneal punctures; Nucleoplasty®; percutaneous access to the brain; and laparoscopy. Various embodiments disclosed herein may be particularly useful when performing procedures on obese patients. As only one example, embodiments disclosed herein may be helpful in preventing complications associated with performing laparoscopy on obese patients. Initial needle placement for insufflation of gas into the peritoneal cavity can puncture organs due to the difficulty of sensing entry into the peritoneal cavity. 
     Various embodiments disclosed herein may be used as part of other procedures, including, but not limited to: detection of cavities, low density tissue, or a fluid-filled cavity within a body; removal of fluid, tissue, an implanted device, or air; addition of fluid, graft tissue, a device, or air; delivery of adhesives, sutures, staples, graft material, or graft substitute; and detection of cancerous tissue or borders of cancerous tissue. Such procedures may be performed as part of human or veterinarian procedures. 
     Placement of a penetrating medical device during a medical procedure is achieved by incorporating a component into a lumen of the medical device that responds to pressure encountered at the tip of the device. The component may be used to sense position and/or as part of a system of controlling advancement of the medical device. 
     According to one aspect of embodiments of the invention disclosed herein, an apparatus is provided that can provide information regarding the resistance of the material in which the tip of the apparatus is located. As the tip is advanced through structures of varying resistances this information may be used to determine the position of the tip relative to those structures. The apparatus provides a response to changes in pressure, force, or other parameter such that when the tip reaches matter of a certain resistance, the apparatus responds. The response may be used to indicate, such as to a human operator or a machine controller, the position of the tip. The response may alternatively or additionally be used to control application of a driving force to the apparatus, such as to remove the driving force when the tip is positioned in a structure of a desired resistance. 
     In one embodiment, a membrane or other flexible element may be provided at the penetrating (distal) tip of the needle and configured such that upon advancement of the needle into a low resistance matter, the membrane at the distal tip of the needle expands, inflates, or otherwise responds to a decrease in resistance. That response may be communicated to the proximal end of the needle or other location where it may be observed or used to control driving force on the apparatus. Change in resistance at the tip may be communicated in any of multiple ways, including by sensing a displacement of fluid from the proximal end to the distal end as the membrane, upon encountering lower resistance, expands. Such a needle may be used in medical procedures in which a needle tip (or other penetrating medical device tip) is to be placed in a bodily lumen, cavity, or other region of material providing low resistance such that a drop in pressure indicates that no further driving of the needle should occur. 
     In other embodiments, the sensed resistance at the tip of the penetrating device may be used to selectively couple a driving force to the penetrating device. For example, a driving force may be coupled to a penetrating medical device, such as a needle, when the apparatus tip encounters material of high resistance. When the tip encounters a low resistance material, no further driving force is applied to the penetrating medical device. For purposes herein, areas of low resistance include cavities containing little or no solid matter. Such a penetrating medical device may be implemented, in some embodiments, with a needle including a force-providing element and a clutch which selectively engages and disengages the penetrating medical device from the force-providing element depending on the resistance of the matter through which the needle is being advanced. 
     In other embodiments, a membrane or other expanding element may be provided at the penetrating (distal) tip of the needle, and configured such that upon advancement of the needle into a low resistance matter, the membrane inflates and retards further needle advancement. 
     In one embodiment, a device that is adapted to penetrate a body includes at least one first member having a distal tip and a lumen having an opening adjacent the distal tip. The device also includes a second member disposed within the lumen, the second member having a structural surface exposed through the opening, and the second member being adapted to have a first state in response to a first pressure on the surface and a second state in response to a second pressure on the surface. 
     In another embodiment, a method of operating a device that is adapted to penetrate a body is provided. The device includes at least one first member having a distal tip and a lumen having an opening adjacent the distal tip, and a second member disposed within the lumen. The second member has a surface exposed through the opening. The method includes advancing the device through a first region of the body, the first region providing a first resistance to penetration of the device, whereby the second member has a first configuration in response to a first pressure on the surface created by the first resistance. The method further includes advancing the device into a second region of the body, the second region providing a second resistance to penetration of the device, whereby the second member has a second configuration in response to the second pressure on the surface created by the first resistance. 
     In a further embodiment, a method of sensing the region of a body in which a section of a penetrating medical device is positioned is provided. The section of the penetrating medical device has a structural surface that is coupled to a fluid held within the penetrating medical device by the structural surface. The method includes inserting the section of the penetrating medical device into the body, and with the section of the penetrating medical device positioned in a first region of the body, sensing a first pressure on the structural surface. With the section of the penetrating medical device positioned in a second region of the body, the method also includes sensing a second pressure on the structural surface. 
     In another embodiment, an apparatus includes a penetrating medical device having a distal tip, and a movable membrane positioned near the distal tip and coupled to a fluid held within the penetrating medical device by the movable membrane. 
     In a further embodiment, a method of positioning a penetrating medical device within a body is provided. The device includes a first element having a distal tip and a second element having a distal surface adjacent the distal tip. The method includes inserting the distal tip into the body with the surface in contact with the body. The method further includes exerting a force on the second element, the force deforming the second element when the distal tip of the penetrating medical device is positioned in a first region having a first resistance to advancement such that the second element engages the first element and transfers at least a portion of the force to the first element, whereby a driving force is applied to the first element which advances the penetrating medical device through the body. 
     In another embodiment, a method of positioning a penetrating medical device within a body is provided. The device includes a first element having a distal tip, and a second element within the first element, the second element having a distal surface adjacent the distal tip. The method includes inserting the distal tip into the body, exerting a force on the second element, and with the distal tip positioned in a first matter having a first resistance to advancement of the penetrating medical device through the body, advancing the penetrating medical device through the first matter. Upon the distal tip reaching a second matter having a second resistance that is lower than the first resistance, exertion of the same force on the second element increases the surface area of the penetrating medical device that is exposed to the body, thereby resisting advancement of the penetrating medical device. 
     In a further embodiment, a medical device that is adapted to penetrate a body includes a first element having a distal tip and a lumen having an opening, and a force-providing element disposed in the lumen. The force-providing element is configured to receive an applied force and selectively transfer at least a portion of the applied force to the first element based at least in part on the resistance of the matter which the force-providing element contacts at the opening. 
     In another embodiment, a device that is adapted to penetrate an object includes a first element configured to have at least a portion advanced into an object, the first element having a channel, and the channel having an opening. The device further includes a force-providing element which is configured to receive an applied force and selectively transfer at least a portion of the applied force to the first element via contact between the force-providing element and an internal surface of the channel. When the force-providing element encounters a first resistance to advancement through the object, the force-providing element has first shape such that sufficient contact exists between the force-providing element and the internal surface of the channel to transmit force from the force-providing element to the first element. When the force-providing element encounters a second resistance to advancement through the object, the second resistance being lower than the first resistance, the force-providing element has a second shape such that insufficient contact exists between the force-providing element and the internal surface of the channel to substantially advance the first element through the object via transmission of force from the force-providing element to the internal surface of the channel. 
     All aspects of the invention need not be present in various embodiments of the invention, and one embodiment may instantiate multiple aspects. Various combinations of aspects and features disclosed herein may be present in embodiments of the invention. Additionally, while certain advantages and features of embodiments are described herein, a device, apparatus, system or method need not necessarily provide every advantage or include every feature to fall within the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior art method of central venous catheter placement within the subclavian vein and into the right side of the heart; 
         FIG. 2  shows a prior art Tuohy needle and associated components; 
         FIG. 3  shows a prior art Tuohy needle being advanced into the epidural space; 
         FIG. 4  shows a stylet according to one embodiment of the invention; 
         FIGS. 5   b  and  5   b  illustrate the advancement of a needle from a high resistance matter into a low resistance matter according to one embodiment of the invention; 
         FIGS. 6   a  and  6   b  illustrate a continuous balloon within a penetrating medical device according to another embodiment of the invention; 
         FIG. 7  illustrates a necked portion of a needle according to one embodiment of the invention; 
         FIG. 8  illustrates a rounded needle tip, according to one embodiment of the invention; 
         FIG. 9  illustrates an inflated balloon according to one embodiment of the invention; 
         FIG. 10  illustrates a mechanical device applying pressure to a fluid within a penetrating medical device according to one embodiment of the invention; 
         FIGS. 11   a  and  11   b  illustrate a penetrating medical device including bellows according to one embodiment of the invention; 
         FIGS. 12   a  and  12   b  illustrate a penetrating medical device according to one embodiment of the invention; 
         FIG. 12   c  illustrates a penetrating medical device according to a further embodiment of the invention; 
         FIGS. 13   a  and  13   b  illustrate an alternative embodiment of a penetrating medical device; 
         FIG. 13   c  illustrates an alternative embodiment of a penetrating medical device; 
         FIGS. 14   a  and  14   b  illustrate a penetrating medical device which includes a high Poisson ratio material according to one embodiment of the invention; 
         FIG. 15  illustrates a penetrating medical device including a mechanical expansion spring according to one embodiment of the invention; 
         FIGS. 16   a  and  16   b  illustrate a sensitivity amplifier according to one embodiment of the invention; 
         FIGS. 17   a - 17   d  illustrate various embodiments of penetrating medical devices including one or more longitudinal channels; 
         FIG. 18  illustrates a device for providing step-wise advancement of a penetrating medical device according to one embodiment of the invention; 
         FIGS. 19   a  and  19   b  illustrate embodiments of a device for providing advancement of a penetrating medical device according to embodiments of the invention; 
         FIGS. 20   a - 20   d  illustrate embodiments of a penetrating medical device having an increased resistance between the penetrating portion and surrounding material according to embodiments of the invention; and 
         FIG. 21  illustrates a flexible wire according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     One example of a penetrating medical device that may be used in embodiments of the invention is a stylet. In one embodiment, as shown in  FIG. 4 , an inflatable, elastic membrane  400  is housed in a distal end  402  of a hollow stylet  404  containing a fluid (e.g., saline). As illustrated in  FIGS. 5   a  and  5   b , stylet  404  is held within a needle  500  as both elements are advanced through tissue. A proximal end  406  of the stylet may include a second membrane  408  that is in communication with membrane  400  as a result of the fluid between them. Exertion of force on one membrane tends to displace the other membrane. 
     In the embodiment illustrated, membrane  408  is configured and positioned similarly to a plunger at the end of a syringe. Such a configuration allows a human operator to exert a force on membrane  408  and to sense the amount of force needed to be applied to membrane  408  to displace membrane  400 . 
     In the embodiment illustrated, membrane  400  is displaced by inflating and the amount of force needed to inflate distal membrane  400  depends on the resistance of the material in which membrane  400  is positioned. The operator detects the penetration of the stylet  404  (and hence a needle tip  502 ) into certain tissues or tissue compartments by haptically sensing changes in resistance while exerting pressure on distal membrane  408 . In the embodiment illustrated, an operator may sense a change in resistance because inflation of membrane  400  causes a displacement of fluid from the proximal end to the distal end, with a corresponding motion of membrane  408 . 
     For example, as shown in  FIGS. 5   a  and  5   b , the amount of force required to inflate membrane  400  may be used to determine when the tip  502  of the needle exits high resistance matter  504  and enters a tissue compartment, such as an epidural space  506 . When needle tip  502  reaches the epidural space  506 , membrane  400  expands because of the pressure being applied to membrane  408  creating a pressure on membrane  400  greater than that generated by the low resistance of epidural space  506 . An operator may haptically sense the pressure change by maintaining contact with membrane  408 . Though any suitable mechanism may be used to sense the change in pressure, including, in some embodiments, a pressure sensor (not shown) which may be coupled to the stylet to sense when a sudden pressure drop occurs, and thus indicate that the epidural space has been reached by tip  502 . 
     For purposes herein, membrane  400  is considered to be a member having a structural surface. In a needle having a distal tip with fluid directly exposed through an opening in the distal tip, the fluid is not considered to have a structural surface exposed through the opening, although the fluid is still considered to be a member. Any suitable material may be used to form membrane  400 . Membrane  400  may be degradable or non-degradable depending on the desired uses of the apparatus and/or the desire characteristics of the apparatus. In some embodiments, membrane  400  and/or membrane  408  may be housed within a needle instead of within a stylet within a needle. Also, a penetrating medical device other than a needle may be used. For example, a trocar or an apparatus without a sharp tip may be used in conjunction with one or more membranes or other embodiments described herein. 
     As needle  500  is being advanced, to prevent membrane  400  from being pushed into the barrel of the stylet, stylet tip  402  may include a protective element (not shown) between membrane  408  and the interior of the stylet. The protective element may be, for example, a meshwork or a fenestrated surface made from synthetic or natural materials which are degradable or non-degradable materials or combinations thereof. In some embodiments, the apparatus may contain a mechanism that prevents the membrane from remaining inflated during withdrawal of the needle. 
     Detection of a dural puncture with prior art epidural needles can be made by observing fluid leakage from the body into the syringe. To permit a similar method of detecting a dural puncture with embodiments disclosed herein, a channel or other longitudinal space may be provided between stylet  404  and interior walls of needle  500 . This channel allows fluid leakage toward the proximal end of the needle so that the operator can observe fluid leakage. 
     Currently used epidural placement methods include removing the stylet from the needle and inserting a syringe filled with air or saline to check for loss of resistance to the injection of air or saline. Sometimes, multiple exchanges of the stylet and the syringe are required. Additionally, in some instances, undesirable amounts of air or saline may be injected into the body. Through the use of various embodiments disclosed herein, an operator may detect entry of the needle tip into specific tissue or tissue compartment without the associated complications of injecting air or saline into the body. By not repeatedly exchanging a syringe and a stylet, a more rapid detection of the epidural space also may be achieved by using embodiments described herein. In addition, opening an inflatable membrane into the epidural space may facilitate passage of a catheter for administration of anesthesia. 
     An apparatus similar to the one illustrated in  FIGS. 5   a  and  5   b  may be used to perform central line placement. When performing central line placement, the operator is able to detect entry into a vein or artery based on relative differences in pressure. Thus, embodiments disclosed herein may be used to quickly assess entry of the needle into various levels of tissue or tissue compartments. By helping to indicate false arterial cannulization, the apparatus provides the operator with time to reposition the needle prior to insertion of large bore catheters, which is the step that results in most of the complications of CVC discussed above. In some embodiments, the apparatus may be configured to attach to currently existing needles and/or syringes. 
     In the embodiment of  FIG. 4  and  FIGS. 5   a  and  5   b , a proximal and a distal membrane are in communication such that resistance encountered at the distal surface is communicated to the proximal membrane for sensing. As described, fluid within a stylet provides communication between the proximal and distal surfaces. However, any suitable mechanism may be used to form those surfaces and to provide communication between those surfaces. According to some embodiments, as illustrated in  FIGS. 6   a  and  6   b , a penetrating medical device such as needle  500  contains a continuous balloon  600  which reaches both the distal tip  502  of the needle and a proximal end  510  of the needle. Continuous balloon  600  may be filled with a biocompatible fluid, for example, saline. 
     In use, a pressure is applied to proximal end  612  such that, while needle tip  502  is positioned within a high resistance matter  604 , as shown in  FIG. 6   a , a distal end  606  of the balloon remains un-inflated or slightly inflated. However, the pressure on surface  612  is such that when needle tip  502  is advanced into a low resistance matter  608 , as shown in  FIG. 6   b , distal end  606  of the balloon inflates. Inflation of the distal end  606  can be sensed at the proximal end, such as by a decreased fluid pressure at a compliant diaphragm  610  at a proximal end  612  of balloon  600 . The decrease in fluid pressure at proximal end  612  of the balloon is significant enough for an operator to sense the change in pressure, or significant enough for a pressure sensor to detect the change. Alternatively or additionally, inflation of distal end  606  may result in a displacement of fluid sufficient to create a noticeable change in volume at the proximal end or be reflected in any other suitable way at an observable location. 
     Initial formation of balloon  600  may occur within needle  502 , or balloon  600  may be manufactured outside of the needle and later inserted into the needle. 
     As shown in  FIG. 7 , needle  500  and balloon  600  may include a necked section  700 . The reduction in diameter at necked section  700  restricts the forward movement of balloon  600  to provide a limit on the distance balloon  600  can travel in the distal direction. 
     As shown in  FIG. 8 , rounded inside edges  800  of needle tip  502  may be provided to help prevent puncturing of the balloon as it inflates and deflates. 
     The shape of balloon  600  as it inflates out of needle tip  502  need not be symmetric or spherical. In some embodiments, one of which is shown in  FIG. 9 , distal end  606  of balloon  600  inflates into a bent shape that takes it out of the direct path of portions of needle tip  502 . In the embodiment illustrated, balloon  600  is shaped so that, as it inflates, it presses against a curved edge and expands away from a sharp edge. 
     It is not necessary that resistance at the tip of a penetrating device be sensed using a proximal membrane. In the embodiment illustrated in  FIG. 10 , needle  500  is coupled to a device  1002  which supplies a pressurized fluid  1004  to the needle. Needle  500  includes a membrane  1006  at the distal end of the needle. A pressure is applied to the fluid by device  1002  such that membrane  1006  either does not inflate or inflates an insignificant amount when needle tip  502  is positioned within a high resistance matter. When the needle tip is advanced into a low resistance matter with an operator&#39;s insertion force, a measurable pressure decrease may be sensed as membrane  1006  inflates. Device  1002  may be a pump box in some embodiments. Though, any suitable effect of membrane  1006  encountering a lower resistance may be sensed. Such effects may include sensing a flow of fluid as membrane  1006  expands or sensing the pressure required to maintain fluid within needle  500  in equilibrium. 
     In embodiments which include a continuous balloon within needle  500 , device  1002  may be coupled to pressurized fluid within the balloon, and upon reaching low resistance matter, the expanding balloon results in a measurable pressure change. 
     The ability to communicate an indication of a resistance at the tip of a device to a more proximal location may be used in ways other than to provide an indication of the location of the tip relative to low resistance spaces. The ability to communicate a force may be used to also control a driving force coupled to the penetrating device so that a driving force is coupled to the penetrating device as it encounters high resistance materials but the driving force is removed when the tip is positioned in a target space, such as in a lumen, such as a vein or artery a spinal column or other low resistance tissue or structure. In the embodiment illustrated in  FIGS. 11   a  and  11   b , bellows  1100  are attached directly to needle  500 . Needle  502  and bellows  1100  contain a fluid, which may be a biocompatible fluid such as saline. When needle tip  502  is positioned within high resistance matter  604 , bellows  1100  remain pressurized because membrane  1006  inflates insignificantly or not at all. Even as bellows  1100  are pushed by the operator to advance the needle, the bellows remain pressurized because less force is needed to advance the needle than to inflate membrane  1006  when advancing the needle tip through the high resistance matter. Once needle tip  502  reaches low resistance matter  608 , however, the force needed to advance the needle is higher than the force that results in inflating membrane  1006 . As a result, further pushing the bellows results in compression of the bellows and inflation of the membrane with the biocompatible fluid. 
     In some embodiments, resistance encountered at the tip of a device may be used to control a clutch mechanism to create an apparatus that provides a driving force to a penetrating medical device when the apparatus tip encounters material of high resistance, and when the apparatus tip encounters a low resistance material, no further driving force is applied to the apparatus. Such an apparatus may be used to stop advancing the tip of a device upon reaching a desired low resistance area, regardless of whether the operator continues to apply force to certain components. 
     In the embodiment illustrated in  FIGS. 12   a  and  12   b , a catheter core  1202  is positioned within a curved needle  1204 . A distal tip  1206  of needle  1202  is partially inserted into a high resistance matter  604  by pushing on the needle. After the needle has been partially inserted, continued advancement of the needle is provided by pushing on catheter core  1202 . Catheter core  1202  does not exit through needle tip  1206  because the high resistance matter present at needle tip  1206  prevents a tip  1208  of the catheter core (which may be a blunt tip) from advancing into the matter. At a certain level of force, catheter core  1202  buckles, and catheter core  1202  contacts the interior of curved walls  1210  of needle  1204 . 
     In the embodiment illustrated, the curved walls act like a capstan to wedge the catheter core in place. With the catheter core wedged, further forces applied to the catheter core are transferred to the needle wall, and the needle advances further through the high resistance matter. When the needle is advanced into a region of low resistance matter, the force resisting the catheter core tip decreases and the catheter core moves through the needle and into the low resistance matter. Allowed to move into the low resistance matter, the catheter core no longer buckles, no longer transfers significant force to the needle wall, and thus advancement of the needle no longer occurs. In this manner, the catheter inside the curved needle acts like a linear force clutch. For purposes herein, a catheter core, or any other suitable element used in a similar manner, is considered to be a member with a structural surface. 
     In some embodiments, needle  1204  may be formed of 17 Gauge thin-walled stainless steel tubing (0.058″ O.D. and 0.048″ I.D.), but may be formed of any suitable material and have any suitable size. Needle  1204  may include any suitable bend radii, but in some embodiments, bend radii of greater than 0.5″ are used. 
     Catheter core  1202  may be any suitable material that is sufficiently pliable to buckle at forces above those encountered as it passes through a material deemed “low resistance,” sufficiently rigid to transmit a force when buckled and sufficiently springy to disengage from the walls of needle  1204 . Examples of suitable materials includes PTFE, PEEK, Nylon, Nitinol, or any metal or other material conventionally used to make catheter guide wires. In some embodiments, catheter core  1202  may have a diameter of less than 0.040 inches. 
     In one specific example of a method of using such an apparatus, a needle is partially inserted into the ligamentum flavum by pushing on the needle, and then further advancement is controlled by pushing on the catheter core. While the needle tip is positioned in the ligamentum flavum, pushing on the catheter core buckles the catheter, thereby pushing the needle further into the ligamentum flavum. Once the needle advances into the epidural space, the catheter core no longer buckles, and no further advancement of the needle occurs. 
     While the curved needle embodiment described above is described as including a catheter core, other suitable force-providing elements may be used. For example, in some embodiments, a flexible wire may be used within the needle to advance the needle through tissue. In still other embodiments, a force-providing element may be implemented on the outside of the needle. 
     As illustrated in  FIG. 12   c , instead of a one-piece needle, one embodiment of which is shown in  FIGS. 12   a  and  12   b , a curved section, such as an S-shaped section  1204 ′ for example, and a straight section  1204 ″ may be separable from one another. A Luer-Lok® connector  1214  or other suitable connector may used to permit selective connection of S-shaped section  1204 ′ and straight section  1204 ″. In some embodiments, S-shaped section  1204 ′ and straight section  1204 ″ may be configured to be separable without the use of a connector. 
     Straight section  1204 ″ may be a standard needle in some embodiments. When straight section  1204 ″ advances to the low resistance material, S-shaped section  1204 ′ may be separated from straight section  1204 ″ and catheter core  1202  may be removed. A catheter (not shown) then may be inserted through straight section  1204 ″. In some embodiments, catheter core  1202  may be left in place when S-shaped section  1204 ′ is removed, and a catheter may be slid over catheter core  1202  and into the low resistance material. 
     As shown in  FIG. 12   c , a hand piece  1212  may be included on the penetrating medical device, for example at the proximal end, to provide a grip area for the operator. In some embodiments, hand piece  1212  is a tube 
     In another embodiment, a straight needle is used with a force-providing element to provide a linear force clutch. As illustrated in  FIG. 13   a , when needle tip  502  is positioned within high resistance matter  604 , a force-providing element, such as flexible wire  1302 , buckles and contacts the interior of the needle walls. Friction with the needle walls transfers the force on the flexible wire to the needle. When needle tip  502  enters low resistance matter  608 , as shown in  FIG. 13   b , flexible wire  1302  no longer buckles and it is released from substantial contact with the needle. The flexible wire is then free to advance without pushing the needle further into the low resistance matter  608 . 
     In some embodiments, one example of which is illustrated in  FIG. 13   c , the medical device may include serpentine portions in both the needle and the wire. As illustrated in  FIG. 13   c , a removable portion of the penetrating medical device may include both a straight section  1306  and an S-shaped section  1308 . Flexible wire  1302  (or other suitable catheter core) may buckle within straight section  1306 , and thereby contact the interior walls of straight section  1306 . Additionally, the curved walls of S-shaped section  1308  act like a capstan to wedge the flexible wire in place. In some embodiments, the flexible wire (or other suitable catheter core) also may buckle within portions of S-shaped section  1308 . 
     For embodiments of the penetrating medical device which include both a straight section and a curved section (e.g., an S-shaped section), a mathematical model has been created to estimate the output force of the catheter core (e.g., a flexible wire) as a function of the axial input force on the catheter core. Equation (1) presented below was developed by modeling the amount of force absorbed by the curved and straight sections of the device, and then subtracting the estimated forces from the input force. By conducting test measurements, a correction factor has been incorporated into the equation. 
     The force for the straight section uses the helical buckling equation while the force for the curved section is for the unbuckled state. For the model, it is assumed that the catheter core is always helically buckling in the straight section while not buckled in the curved section. The force output by the catheter core is modeled to be:
 
 F   out predicted   =F   in −(μ L   curved   F   in   /R+ 10μ D   core   F   in   2   r /( EI ))  (1)
 
where μ is the coefficient of friction between the catheter core and the interior wall, L curved  is the length of the interior of the curved section (m) that the catheter core is touching, F in  is the input force (N) applied at the hand piece, D core  is the diameter of the catheter core (m), R is the average radius of the curves in the curved section (m), r is the radial gap spacing between the catheter core and the interior wall (r), E is the modulus of elasticity (N/m 2 ) of the catheter core, and I is the moment of inertia of the catheter core (m 4 ).
 
     The embodiments of  FIGS. 12   a ,  12   b ,  12   c ,  13   a ,  13   b , and  13   c  provide examples of apparatus including a force translating member that translates an axial force, generated by resistance encountered at the tip of a medical device, to a transverse force, such as a radial force. Such force translation allows a driving member, such as a catheter core, to selectively engage a needle based on resistance encountered. Other suitable elements may be used to create a “clutch” to selectively drive a penetrating medical device. 
     Another type of suitable element is illustrated in  FIGS. 14   a  and  14   b . A material or device having a high Poisson ratio (hereinafter, “Poisson element”) may be used as part of an apparatus which provides a linear force clutch for controlling advancement of a penetrating medical device. In some embodiments, the Poisson element may be a balloon or an elastomer. In the embodiment illustrated in  FIGS. 14   a  and  14   b , an element  1402  including high Poisson ratio material acting as a Poisson element is coupled to a force-providing core  1404 . When the core is pushed with needle tip  502  positioned in high resistance matter  604  such that a distal end  1406  of core  1404  cannot substantially exit needle tip  502 , Poisson element  1402  is compressed and expands radially. Once sufficiently expanded, the Poisson element contacts the interior walls of needle  500 , and the operator&#39;s compressive force on core  1404  is transferred to the needle walls, thereby advancing the needle. Once the needle tip advances into low resistance matter  608 , distal end  1406  of core  1404  advances through the low resistance matter, the compressive force on the Poisson element decreases, and the Poisson element no longer significantly contacts the needle walls. In this manner, further pushing on core  1404  does not further advance needle  500 . 
     As an example of another embodiment of a Poisson element, a mechanical expansion spring may be used to selectively transmit force from a core to the needle walls. As shown in  FIG. 15 , a mechanical expansion spring  1502  includes two flexible spring members  1504  which are displaced radially when a compressive axial force is applied via core  1404 . With sufficient axial force, flexible spring members  1504  contact the interior needle walls and the friction transfers the force of the core  1404  to needle  500 . The mechanical expansion spring is configured to expand sufficiently radially (direction B) when the resistance of expected high resistance matter is encountered by the distal end of core  1404  as needle  500  is being advanced through the high resistance matter. When the needle tip advances into expected low resistance matter, the core is free to extend out of the needle, allowing the expansion spring to elongate in the axial direction (direction A) and retract in the radial direction, thereby ending its contact with the needle walls. Accordingly, further advancement of the needle does not occur within the low resistance matter. While the embodiment illustrated in  FIG. 15  includes two flexible spring members, three, four, or more than four flexible spring members may be included in some embodiments. 
     A sensitivity amplifier may be employed in some embodiments to amplify the effect of a change in resistance encountered at the tip of a penetrating medical device. Such amplification may improve the reliability with which a clutch engages or help an operator observe changes in the material through which the needle tip is advancing. For example, as illustrated in  FIGS. 16   a  and  16   b , a needle  1600  may have a distal section  1602  with a first diameter and a proximal section  1604  with a second, smaller diameter. As a piston  1606  is pushed into proximal section  1604 , a release of biocompatible fluid from the distal section that is equal to the volume of fluid occupying a longitudinal length of tout will permit piston  1606  to move a longer, longitudinal length of Δin because the cross-sectional area of proximal portion  1604  is less than the cross-sectional area of distal section  1602 . This embodiment of a sensitivity amplifier may be used with a needle having no membrane at needle tip  502 , or it may be used with a needle that has a membrane at the needle tip (similar to the embodiment illustrated in  FIGS. 11   a  and  11   b ). A sensitivity amplifier may be used with other embodiments described herein, and other suitable sensitivity amplifiers may be used to aid with the sensing of needle advancement. 
     An operator may prefer to retain an open channel within the penetrating medical apparatus. For example, in some cases, the operator may desire to observe fluid flowing from the body to help determine the location of the needle tip. In some cases, the operator may wish to inject fluid into the region in which the needle tip is placed. To accommodate fluid flow through the needle, various embodiments of needle and/or core arrangements may be put to use. 
     For example, as shown in  FIG. 17   a , core  1702  may have a diameter that contacts or almost contacts an interior surface  1704  of the needle walls around most of the perimeter of the core. In one or more areas, however, a space  1706  may be formed between core  1702  and interior surface  1704  with a section  1708  of the core that has a smaller radius. The space  1706  forms a longitudinal channel through which fluid may flow. 
     A hollow core  1712  may be used in some embodiments to provide a channel, as illustrated in  FIG. 17   b . The core  1712  reaches or nearly reaches the interior surface of the needle around the entire perimeter of the core, but a channel  1714  is provided through the interior of the core. 
     In another embodiment, as illustrated in  FIG. 17   c , a substantially solid needle  1718  may be used as a penetrating device, and a portion  1720  of the solid material may have a reduced radius. A needle wall  1722  forms a flow space  1724  in conjunction with reduced radius portion  1720  of the solid needle. 
     In still a further embodiment of a channel within a penetrating medical device, a flow channel may be formed within the area between the needle wall and the outside of a core, and also within a hollow core (or cores). For example, as illustrated in  FIG. 17   d , two hollow cores  1730  and  1732  may form two channels  1734  and  1736 . Additional channels  1738  and  1740  may be formed between the exterior of the cores  1730 ,  1732  and the interior surface  1704  of needle  500 . In this manner, multiple channels may be formed for fluid feedback, fluid injection, or any other suitable purpose. 
     A multi-channel device may be configured to allow fluid flow in one or more channels, and the presence of a core and/or Poisson element in another channel. In this manner, separated channels may be used for different purposes. In some embodiments, a first channel may be used for holding pressurized fluid to be used as part of a sensing arrangement, and a second channel may be used to deliver fluid to the body. 
     The penetrating medical devices described herein may further employ an advancing arrangement which limits the advancement of a core such as a catheter core, a flexible wire, etc., even when low resistance matter is encountered. For example, as illustrated in  FIG. 18 , a device  1800  with a trigger handle  1802  may be used to push on core  1404 . Each complete pull of trigger handle  1802  advances core  1404  out of device  1800  by a certain distance. When core  1404  is wedged in curved needle  1204 , needle  1204  advances by the same distance. Once the needle tip reaches matter with a low resistance, the core advances in a step-wise manner into the low resistance matter, such that each discrete motion of the operator advances the core at most by the distance provided by one complete pull of the handle. In this manner, unintentional advancement of core  1404  into low resistance matter can be limited. Device  1800  is shown by way of example only, and other suitable devices and methods may be used to limit the advancement of core  1404  upon encountering a low resistance material, such as by limiting advancement to a discrete distance. 
     Another embodiment of an advancing arrangement for use with penetrating medical devices described herein is illustrated in  FIG. 19   a . A grip tube  1900  holds flexible wire  1302  at a grip location  1902 . Grip tube  1900  has a diameter that is slightly larger than straight needle  500  such that grip tube  1900  may be translated axially relative to needle  500 . Grip tube  1900  provides off axis stability to one or both of the needle and the flexible wire. In an alternative embodiment, as illustrated in  FIG. 19   b , a rigid rod  1904  may be used to apply force to flexible wire  1302 . As with various embodiments disclosed herein, when needle tip  502  is positioned within high resistance matter, a force-providing element, such as flexible wire  1302 , buckles and contacts the interior of the needle walls. Friction with the needle walls transfers the force on the flexible wire to the needle. When needle tip  502  enters low resistance matter, flexible wire  1302  no longer buckles and it is released from substantial contact with the needle. The flexible wire is then free to advance without pushing the needle further into the low resistance matter. Either of the advancing arrangements illustrated in  FIGS. 19   a  and  19   b  may be used as a stand-alone device, or may be used in combination with other components, such as a step-wise advancing device similar to the embodiment illustrated in  FIG. 18 . In some embodiments, grip tube  1900  may be sized and configured to translate axially along the interior of needle  500 . 
     When using various embodiments disclosed herein, sufficient resistance may not exist between the penetrating medical device and the surrounding material to stop advancement of the penetrating medical device when it reaches low resistance material. In various embodiments disclosed herein, the needle may include one or more features that increase the resistance between the needle and the surrounding material. For example, as shown in the side view of  FIG. 20   a , an outer surface of needle  500  may include an area of surface roughness  2002  that is higher than a standard needle. As illustrated in the cross-sectional view of  FIG. 20   b , needle  500  may have a first section  2004  with a first outer diameter and a second section  2006  having a larger outer diameter than first section  2004 . The change in diameter creates an increased resistance to advancement. The cross-sectional view of  FIG. 20   c  shows needle  500  having first section  2004  with a first outer diameter and second section  2006  having a larger outer diameter than first section  2004 , and additionally includes a transition section  2008  between first section  2004  and second section  2006 . In an alternative embodiment, needle  500  may include a very short or non-existent first section  2004 , such that transition section  2008  is positioned close to or at the distal tip of needle  500 .  FIG. 20   d  shows a cross-sectional view of a needle  500  having a curved bump  2010  that extends around the circumference of the needle. In an alternative embodiment, a toroidal-shaped component may be positioned around the circumference of the needle. In another embodiment, a semi-spherical bump may be included at one or more distinct positions on the needle. 
     The particular arrangements and sizes of any features that increase resistance with surrounding material may be based on the type of material being penetrated and the type of space being targeted. 
     One embodiment of a catheter core, such as flexible wire  1302  for example, is shown in a cross-sectional view in  FIG. 21 . In this embodiment, flexible wire  1302  has a lumen  2102  and one or more passages  2104  that lead to lumen  2102  through the wall of flexible wire  1302 . Lumen  1302  may be used for insufflation, drug delivery, or drainage of excess bodily fluids in some embodiments. Lumen may be used to inject fluid when a target region is reached by the penetrating medical device. The injection of fluid may be provided by using bellows. In some embodiments, a balloon may be provided within the lumen of flexible wire  1302 , and the balloon may be filled with a fluid to provide pressure feedback to the operator. 
     In various embodiments described above, a membrane is provided at a needle tip. In some embodiments, needle tip may be left open and optionally may have a restricted diameter opening. In such embodiments, fluid at the opening may not have a structural surface, but high resistance matter nonetheless may prevent biocompatible fluid from exiting the needle tip, while low resistance matter may allow the fluid to flow from the needle tip. Similar to the inflation of a membrane in low resistance matter, the initiation of flow from the needle tip decreases the pressure sensed by the operator, indicating advancement into low resistance matter. 
     In embodiments which include a membrane or balloon at the needle tip, in addition to providing an indication of reaching low resistance matter, inflation of the membrane or balloon may serve to prevent or reduce further advancement of the needle tip into low resistance matter. For example, an inflated membrane or balloon may block the sharp edge of the needle and/or present a large surface area which cannot be advanced through the low resistance matter. 
     Also, an embodiment was described in which a catheter core was used as a driving element. There is no requirement that the driving element be at the center of a catheter.  FIGS. 17   a - 17   d  illustrate various multi-lumen devices and the driving element may be configured in any of suitable lumen or otherwise constrained in a desired position. 
     Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.