Abstract:
The present invention discloses a pressure-depending clutching device for locating and safely positioning a needle in a body cavity. The device is capable of automatically engaging and disengaging the needle from a driving force depending on the pressure experienced by needle. The device has a body with an interior space, a pressure-sensing element disposed in the body defining a portion of a pressure chamber, and a force-receiving element operatively connected to the pressure-sensing element. The force-receiving element has a shape complimentary to a portion of a force-sending element operatively connected to a force-applying structure such as a handle for a user to apply a driving force. The pressure-sensing element, the force-receiving element, and the complementary force-sending element form a driving force engaging mechanism for coupling the force-applying structure to the needle during operation. Before the needle reaches the target body cavity, the pressure in the needle causes the clutching device to assume an “engaged” state, coupling the driving force to the needle. When the needle reaches the body cavity, the change in pressure causes the clutching device to assume a “disengaged” state, disengaging the driving force from the needle, thereby, automatically positioning the needle in the cavity to avoid overshooting. Also provided are needle-and-syringe assemblies incorporating the disclosed clutching devices, methods for manufacturing the disclosed clutching devices, as well as methods for safely locating and positioning needles in the body cavity utilizing a needle-and-syringe assembly incorporating the disclosed clutching devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) and the benefit of U.S. Provisional Application No. 62/091,199, filed Dec. 12, 2014, titled “POSITIONING DEVICE FOR NEEDLE SYRINGE”. This application also claims foreign priority under 35 U.S.C. §119(b) and the benefit of Taiwanese Patent Application number P144228TW, filed Nov. 21, 2014, entitled, “A POSITIONING DEVICE FOR NEEDLE SYRINGE.” The entire disclosures of the above referenced applications are each incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    This disclosure relates generally to the field of needle syringe positioning. More particularly, the present invention relates to devices and methods for safely positioning a needle syringe in a body cavity of a subject such as the epidural space. 
       BACKGROUND OF THE INVENTION 
       [0003]    During medical procedures, locating and accessing a body cavity is often a required step for therapeutic, anesthetic, and diagnostic purposes. For example, procedures such as epidural injection, emergency tracheotomy, chest tube drainage, and percutaneous gastrostomy fistula all require accurately locating and accessing an implicated body cavity with a needle. These puncturing procedures bear high risk factors. When the needle is inserted too far or not far enough, catastrophic consequences can often result. 
         [0004]    Using epidural injection as an illustrative example, this procedure requires positioning the tip of a needle precisely in the epidural space (also known as the epidural cavity) in order to administer pain-killing medicine. The epidural space is an anatomic space located at the outermost portion of the spinal canal, lying in between the ligamenta flava and the dura mater. In humans, the epidural cavity contains lymphatics, spinal nerve roots, loose connective tissue, fatty tissue, small arteries, and a network of internal vertebral venous plexuses. It is only about 3-5 mm wide. Inserting a needle beyond the epidural space can easily cause spinal cord injuries and other medical complications. Hence, it is very important to be able to accurately locate this body cavity. 
         [0005]    Conventional methods for locating the epidural space generally rely on the manual skills of the operator (e.g. anesthesiologist, nurse, etc.). To perform an epidural injection using a conventional method, the operator will have to place the patient in a proper position first. Next, the operator will insert a needle into the spinal column of the patient. Once the tip of the needle enters the deeper part of the interspinous ligament, the operator will hold the needle in place and attach a saline or air filled syringe to the bub of the needle. Along with the syringe, a shaft or wing-shaped handle is typically mounted on the hub for the operator to apply an advancing force to drive the needle further into the body. As the operator pushes on the handle to move the needle forward, he will also push on the plunger of the syringe at the same time to maintain a pressure within the syringe barrel. Before the needle reaches the epidural space, there is no place for the air or saline to go, so a back pressure will be built up within the syringe barrel. This way, the operator will feel a sudden loss of resistance (LOR) when the needle reaches the epidural space as the air or saline is ejected into the epidural space. This sudden LOR allows the operator to know when to stop advancing the needle. 
         [0006]    The above described conventional method is highly subjective, technically demanding, and prone to human error. It also takes much longer to locate the space as the operator must do it slowly to avoid missing the 3-5 mm space. Any slight inertial movement of the hand can easily move the needle pass beyond the epidural space, causing dural puncture and nerve damage. 
         [0007]    Numerous attempts have been made in the art to address this problem. One approach focuses on providing a visual cue to assist the operator in knowing when the needle has reached the epidural space. For example, U.S. Pat. No. 7,175,608 B2 to Hasan teaches a representative device for locating the epidural space that utilizes a diaphragm to provide a visual cue to the operator for indicating when the needle has reached the epidural space. In Hasan&#39;s device, the diaphragm is adapted for pressurization such that when the device is pressurized, it bulges outwards to provide a visual indicator of the pressure change. Many other prior art methods and devices teach various means for similarly providing visual cues to indicate that the needle has reached the epidural space. However, these devices and methods do not solve the fundamental problem of operator error because they still must rely on the human operator to heed the warning and stop advancing the needle. 
         [0008]    U.S. Pat. No. 8,715,234 B2 to Bethi teaches a device for locating a needle in a body cavity that purports to be able to automatically stop advancing the needle once the needle has reached the body cavity. The device works by balancing the frictional force between the needle and the ligament against the back pressure within the syringe barrel. It includes a syringe encased by a frame that is solely connected to the plunger of the syringe. While the needle is in the ligament, the back pressure within the barrel of the syringe will exceed the frictional force between the needle and the ligament so that when the operator pushes the plunger forward, the back pressure will act to advance the entire syringe/needle assembly forward. Upon entering the body cavity, the content of the syringe barrel will be released, thereby relieving the back pressure. At this point, the needle will be held in place by friction between the needle and the ligament while the plunger will advance to empty the contents of the syringe. 
         [0009]    While the device of Bethi purports to be able to stop the needle upon entering the targeted cavity, it requires bulky construction and is not compatible with existing setup commonly found in medical facilities. In actual practice, Bethi&#39;s device further suffers from several other drawbacks. For example, because Bethi&#39;s device relies on balancing the air pressure in the syringe barrel against the friction between the needle and the ligament, the compressible nature of air will create an inherent instability in the needle-syringe assembly. This means that fine control of the needle is basically impossible, making it difficult for a user to precisely place the needle and further increasing the risk of damaging surrounding tissues. Moreover, the device relies on the negative pressure difference between the target cavity and the ligament; hence, it only works for cavities that have negative pressures relative to the ligament (e.g. the epidural space). For cavities that have higher pressure relative to the ligament (e.g. chest cavity), Bethi&#39;s device will not work. 
         [0010]    Therefore, there still exists an urgent need for more universally applicable methods and devices of locating body cavities and placing needles therein without high risk of puncturing surrounding vital structures. 
       SUMMARY OF THE INVENTION 
       [0011]    In the present invention, the problem of locating a body cavity and positioning a needle therein without accidentally overshooting the cavity to cause tissue damage is solved by a pressure-dependent clutching device capable of automatically engaging and disengaging the needle from a driving force based on the pressure differential inside and outside of the cavity. 
         [0012]    In the context of the present invention, the term “clutching device” refers to a device capable of engaging and disengaging two working parts such that forces applied to one working part is transmitted to another working part only when the clutching device is placed in an “engaged” state. A “pressure-dependent clutching device” refers to a clutching device modulated by pressure. Such a device will be able to automatically switch between an “engaged state” and a “disengaged state” depending on whether a threshold external pressure has been encountered. Occurrence of such threshold pressure is herein referred to as the “threshold-crossing event.” Using epidural injection as an illustrative example, when a needle-and-syringe assembly incorporating a pressure-dependent clutching device of the present invention is inserted into a patient, the pressure-dependent clutching device may assume an “engaged” state that couples the needle to a driving force to advance the needle further towards the epidural space. Upon reaching the epidural space, the needle will experience a pressure change, i.e. the threshold-crossing event. This pressure change will then trigger the pressure-dependent clutching device to automatically assume a “disengaged” state to uncouple the driving force from the needle. In this “disengaged” state, any driving force applied to the needle-and-syringe assembly will not be transmitted to the needle, thereby, ensuring that the needle does not move beyond the epidural space. With the aid of the clutching device, a user can simply apply a continuous driving force to the needle without worrying about overshooting the epidural space as the clutching device will act as safeguard to automatically disengage the driving force from the needle upon reaching the epidural space. 
         [0013]    Accordingly, in one aspect, the present invention provides a pressure-dependent clutching device for automatically engaging and disengaging a needle from a driving force. Clutching devices in accordance with this aspect of the invention will generally include a body having an internal space, a pressure-sensing element defining a portion of a pressure chamber disposed in the interior space, and a force-receiving element operatively connected to the pressure-sensing element. 
         [0014]    The term “operatively connected” as used herein encompasses both direct structural connection and indirect function connection so long as the connecting pair is configured to work together to accomplish a common function during operation. For example, a pin structurally connected to a disc that forms the shape of a piston may be considered to be operatively connected during a piston stroking operation. A pair of magnets configured to move in unison without physical contact may also be considered to be operatively connected in a force transmission operation that transmits a force from one magnet to the other. 
         [0015]    During operation, the force-receiving element of the clutching device together with a complementary force-sending element forms a driving force engaging mechanism for engaging and disengaging the driving force. The force-sending element is operatively connected to a force-applying structure for receiving a driving force. When an operator applies a driving force to the force-applying structure, the driving force must go through a force transmission channel defined by the driving force engaging mechanism going from the force-sending element to the force-receiving element. This way, the driving force engaging mechanism can modulate the transmission of the driving force by engaging and disengaging the force-sending/receiving element pair. The driving force engaging mechanism is in turn modulated by the pressure-sensing element so that combined together, the pressure-sensing element and the driving force engaging mechanism work in conjunction to modulate the engaging and disengaging state of the clutching device according to an external pressure. The body of the device provides a housing for the various components of the device. 
         [0016]    Numerous specific implementations of the clutching device are possible. In some embodiments, the clutching device may be implemented as a standalone unit apart from the needle and the syringe. In other embodiments, the clutching device may be implemented as an integral construct of the needle-syringe assembly. In some embodiments, the body of the clutching device may further include connection points for connecting to a needle and a syringe. For example, the body may include a first opening adapted to connect to a needle and a second opening adapted to connect to a syringe. The first opening may place the pressure-sensing element in pressure communication with the needle so that any change in the external pressure is immediately communicated to the pressure-sensing element. 
         [0017]    The pressure-sensing element may be a mechanical structure, an electronic implement, an electromechanical implement, or a combination thereof. In some preferred embodiments, the pressure-sensing element is a mechanical structure. In one exemplary preferred embodiment, the pressure-sensing element is a flexible membrane able to switch between a concave and a convex shape. The flexible membrane may also form a wall of the pressure chamber. During operation, the chamber is placed in pressure communication with an external pressure via the needle so that when a threshold-cross event is encountered (i.e. a pressure change in the external pressure above or below a threshold), the membrane will switch shape from concave to convex and vice versa. Once the threshold-cross event is encountered, the change of state in the pressure-sensing element is relayed to the driving force engaging mechanism to cause a change in the engagement state of the clutching device so that the driving force applied to the force-applying structure may be allowed to engage or disengage the needle. 
         [0018]    The force-applying structure is preferably external to the clutching device. In some preferred embodiments, the force-applying structure is a free-standing handle apart from the needle and syringe, more preferably a wing-shaped handle. 
         [0019]    The driving force engaging mechanism may also be implemented with various structural configurations. In some embodiments, the force-receiving and force-sending element pair of the driving force engaging mechanism is a “pin-and-hole” pair structure. In such embodiments, the pin functions as the force-receiving element of the mechanism and is operatively connected to the pressure-sensing element. The hole functions as the force-sending element of the mechanism and is located on the force-applying handle such that when the external pressure calls for an “engaged” state, the pin is pushed into the hole to couple the needle with the force-applying handle. When the external pressure calls for a “disengaged” state, the pin is withdrawn from the hole to uncouple the handle from the needle. 
         [0020]    The pin-and-hole pair is but only one illustrative pairing. Those skilled in the art will readily recognize that other complementary structural pairs may be advantageously used to implement the driving force engaging mechanism. Exemplary structural pairs may include, but not limited to, a hook and a hook catch in the form of a hole or a toothed rail track, a pair of complementary toothed tracks, and any other structures with complementary geometric shapes. 
         [0021]    In some embodiments that use mechanical structural pairs to form the driving force engaging mechanism, a “sticky pin” problem may occur where the friction between the force-receiving element and the force-sending element may prevent withdrawal of the force-receiving element from the force-sending element. For example, when a pin-shaped force-receiving element becomes engaged with a hole-shaped force-sending element in a glove-over-fist fashion, the frictional force resulting from the surface contact between the surface of the pin and the inner wall of the hole may become too great for the pin to withdraw from the hole. Thus, in some preferred embodiments, the force-receiving element and the complementary force-sending element are configured such that the friction between the force-receiving element and the force-sending element is not sufficient to prevent withdrawal of the force-receiving element from the force-sending element. This may be accomplished by adopting geometries in which frictional force is minimized or eliminated between the force-receiving element and the force-sending element. For example, when the driving force engaging mechanism is a pin-and-hole pair, the pin may be configured to engage the hole at an angle so that the pin does not go into the hole completely, but instead wedges the hole at an angle. This way, the contact between the pin-and-hole pair does not create any friction to prevent withdrawal of the pin from the hole. 
         [0022]    In another preferred exemplary embodiment, the force-sending element may include a gear mechanism having a first gear wheel and a second gear wheel bound together through a common shaft. In this embodiment, the first gear may be operatively connected to the force-applying structure while the second gear may be interfacing with the force-receiving element. In this embodiment, the amount of force needed to engage and disengage the force-receiving element from the gears may be adjusted through the ratio of the gear wheel sizes. 
         [0023]    In the above described embodiments, the pressure-sensing element is described as being implemented with a mechanical structure. In embodiments where the pressure-sensing element is implemented with electronic, electromechanical, or other combinations, the general principle of coupling the external pressure change to a corresponding engagement state of the clutching device via the driving force engagement mechanism will remain the same. Those skilled in the art will be able to devise specific implementations following this general principle. 
         [0024]    Construction material and shape of the various components of the clutching device are not particular limited. Exemplary material for forming the body may include plastics, metals, or any other suitable material commonly known in the art. The body may have regular geometric shapes such as cube or cylinder. It may also be configured to have irregular shapes to better accommodate the overall shape of the needle-and-syringe assembly. 
         [0025]    Exemplary membrane material for forming the pressure-sensing element may include silicon rubber, polyvinyl chloride (PVC), thermoplastic rubber (TPR), polyethylene (PE), metal film, or any other suitable material known in the art. 
         [0026]    While the above described clutching device is capable of automatically engaging and disengaging from a driving force without human input, in some use cases, it is still desirable to provide feedback to the human operator about the engagement state of the clutch or the pressure level sensed by the pressure-sensing element. Thus, in some further embodiments, the clutching device may further include a visual cue to indicate an “engaged” or “disengaged” state or a pressure state. Exemplary visual cue may include but not limited to a viewing window on the body of the device for a user to see the internal state of the clutch, or an electrical signal modulated by the state of the pressure sensing element. In one exemplary embodiment, a membrane pressure sensing element may be coated with an electrical conducting material such that the membrane effectively functions as an electrical switch. In such embodiments, when the membrane is caused to adopt one configuration, it may be brought into contact with a current, which in turn may be coupled with a signaling device such as an LED to indicate the state of the pressure. When the pressure causes the membrane to adopt an alternative configuration, the current is cut-off, resulting in the LED being turned off to indicate the change of state. It will be understood by those skilled in the art that this electrical signaling is not only suitable for providing a visual cue, but may also be configured to control the engagement and disengagement of the driving force engaging mechanism. 
         [0027]    Preferably, clutching devices are implemented as independent units apart from the needle and syringe. Connection of the clutching device to the needle and syringe may be done directly via openings on the body of the device or indirectly via a connecting tube. 
         [0028]    Connecting tubes suitable for connecting clutching devices of the present invention to a needle and a syringe will generally have a tubular body configured to have an end for connecting to a syringe and another end for connecting to a needle. In between the two ends, a portion of the connecting tube may be configured to connect to a clutching device of the present invention. 
         [0029]    In still some other embodiments, the connecting tube may also be configured to include a frame for receiving a syringe. 
         [0030]    Optionally, the clutching device may form an integral part of the syringe. In some exemplary embodiments, the body of the device may have an interior space configured to slidably receive a syringe. In such embodiments, the force-applying structure and the body of the clutching device form a single unit. The needle and syringe are coupled to the body of the clutching device via a driving force engaging mechanism formed by a pair of complimentary structures that includes the force-receiving element of the clutching device and the complementary force-sending element disposed on the body of the clutching device. 
         [0031]    In another aspect, the present invention further provides a syringe-and-needle assembly capable of automatically disengaging from a driving force upon reaching a body cavity of a subject that has a pressure differential between the inside and the outside of the cavity. Embodiments in accordance with this aspect of the invention generally include a needle, a syringe, and a pressure-dependent clutching device as described above. 
         [0032]    The types of needles and syringes are not particularly limited. Those skilled in the art will be able to choose the needle and syringe pair suitable for a particular purpose. In some preferred embodiments, the needle is preferably one suitable for epidural injection such as a Touchy needle or a Hustead needle, but not limited thereto. Exemplary syringes that may be used include loss-of-resistance (LOR) syringe, or a silicone syringe, but are not limited thereto. 
         [0033]    During operation, it is desirable to prevent backflow of pressure towards the syringe barrel once the initial pressure is established within the pressure chamber of the clutching device so that loss of pressure can only occur due to pressure difference of the target cavity. Therefore, in some embodiments, clutching devices may further include a unidirectional valve to prevent backflow of air or fluid to the syringe end. 
         [0034]    In yet another aspect, the present invention also provides a method for forming a pressure-sensitive clutching device suitable for automatically engaging and disengaging a needle from a driving force. Methods in accordance with this aspect of the invention will generally include the steps of forming a body having an interior space, placing a force engaging element and a pressure sensing element inside the body such that the force engaging element is operatively connected to the pressure sensing element and the pressure sensing element form a portion of a pressure chamber within the interior space. The pressure chamber is in pressure communication with an opening on the body of the device, wherein the opening is adapted for connecting to a needle. Embodiments for the force engaging element and the pressure sensing element are as described above. 
         [0035]    In yet another aspect, the present invention also provides a method for positioning a needle in a body cavity of a subject defined by a structural layer of the subject. Embodiments in accordance with this aspect of the invention will generally include the steps of providing a needle-and-syringe assembly as described above; ensuring the pressure-dependent clutching devise is placed in an engaged state; and applying a continuous driving force on the force-applying structure to move the needle-and-syringe assembly forward until the pressure-dependent clutching device automatically disengages the driving force from the needle upon reaching the body cavity. 
         [0036]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  shows an exemplary needle-and-syringe assembly incorporating a pressure-dependent clutching device in accordance with embodiments of the invention. 
           [0038]      FIGS. 2  shows an exemplary connecting tube in accordance with embodiments of the invention. 
           [0039]      FIG. 3  shows another perspective view of the exemplary connecting tube of  FIG. 2 . 
           [0040]      FIG. 4  shows a perspective view of an exemplary force-applying structure configured to be coupled with a clutching device in accordance with embodiments of the present invention. 
           [0041]      FIG. 5  shows a cutaway view of an exemplary clutching device illustrating the relationships between the various elements of the device in accordance with embodiments of the invention. 
           [0042]      FIG. 6  shows a sectional view of an exemplary clutching device in accordance with embodiments of the invention with the force-receiving element in an “engaged” state. 
           [0043]      FIG. 7  shows another sectional view of an exemplary clutching device in accordance with embodiments of the invention with the force-receiving element in an “disengaged” state. 
           [0044]      FIG. 8  shows a cutaway view of an exemplary pressure-dependent clutching device with integrated force-applying handle in accordance with embodiments of the invention. 
           [0045]      FIG. 9  shows a cutaway view of the exemplary embodiment of  FIG. 8 . 
           [0046]      FIG. 10 -A shows a sectional view of the exemplary embodiment of  FIG. 8 . The driving force engaging mechanism is shown in a “disengaged” state. 
           [0047]      FIG. 10 -B shows another sectional view of the exemplary embodiment of  FIG. 8 . The driving engaging mechanism is shown in an “engaged” state. 
           [0048]      FIG. 11 -A shows a sectional view of a clutching device that illustrates an exemplary embodiment of a complimentary structural pair forming the driving force engaging mechanism. The mechanism is shown in an “engaged” state. 
           [0049]      FIG. 11 -B The same mechanism in  FIG. 11 -A is shown in a “disengaged” state. 
           [0050]      FIG. 12 -A shows a sectional view of a clutching device that illustrates another exemplary embodiment of a complimentary structural pair forming the driving force engaging mechanism. The mechanism is shown in an “engaged” state. 
           [0051]      FIG. 12 -B The same mechanism in  FIG. 12 -A is shown in a “disengaged” state. 
           [0052]      FIG. 13 -A shows a sectional view of a clutching device that illustrates yet another exemplary embodiment of a complimentary structural pair forming the driving force engaging mechanism. The mechanism is shown in an “engaged” state. 
           [0053]      FIG. 13 -B The same mechanism in  FIG. 13 -A is shown in a “disengaged” state. 
           [0054]      FIG. 14  shows a cutaway view of an exemplary needle-and-syringe assembly incorporating a locking device in accordance with embodiments of the invention. 
           [0055]      FIG. 15  shows a perspective view of an exemplary connecting tube with a syringe receiving frame in accordance with embodiments of the invention. 
           [0056]      FIG. 16  shows a cutaway view illustrating the body of the clutching device and the force-applying structure in  FIG. 14 . 
           [0057]      FIG. 17 -A shows a sectional view of an exemplary needle-and-syringe assembly incorporating a pressure-dependent clutching device in accordance with embodiments of the invention. The driving force engaging mechanism in this embodiment is shown in an “engaged” state. 
           [0058]      FIG. 17 -B The driving force engaging mechanism in the same embodiment in  FIG. 17 -A is shown in a “disengaged” state. 
           [0059]      FIG. 18  shows a cutaway view of an exemplary pressure-dependent clutching device with the force-applying structure having a force sending element that is engaged by the force-sending element in accordance with embodiments of the invention. 
           [0060]      FIG. 19  illustrates the general process of locating and positioning a body cavity using an exemplary needle-and-syringe assembly endowed with a pressure-dependent clutching device in accordance with embodiments of the invention.  FIG. 19 -A,  FIG. 19 -B,  FIG. 19 -C and  FIG. 19 -D each shows an exemplary step of the process in sequence. 
           [0061]      FIG. 20 -A: Illustrates an exemplary embodiment that experiences a “sticky pin” problem caused by friction. 
           [0062]      FIG. 20 -B illustrates one exemplary embodiment that overcomes the “sticky pin” problem shown in  FIG. 20 -A by utilizing a gear system. 
           [0063]      FIG. 20 -C illustrates another exemplary embodiment that overcomes the “sticky pin” problem shown in  FIG. 20 -A by utilizing an advantageous geometry. 
       
    
    
     DETAILED DESCRIPTION 
       [0064]    Referring first to  FIG. 1 , there is shown an exemplary embodiment of a pressure-dependent clutching device  2  connecting a needle  10  to a syringe  12  via a connecting tube  20 . The clutching device  2  has a body with an interior space  22  and a pressure-sensing element disposed therein. The pressure-sensing element (not shown) is operatively connected to a force-receiving element  26  for engaging and disengaging a force-sending element that relays a driving force from a force-applying structure in the form of a wing-shape handle  24 . Together, the needle  10 , the wing-shaped handle  24 , the clutching device  2 , the connecting tube  20 , and the syringe  12  form an exemplary needle-and-syringe assembly  1  capable of automatically disengaging a driving force depending on the external pressure encountered by the needle. 
         [0065]    During operation, a user pushes on the handle  24  to apply a driving force to move the needle forward. Initially, the pressure within the internal space  22  of the clutching device  2  is sufficient to cause the force-receiving element  26  to engage the force-sending element so that the force applied to the wing-shaped handle  24  is transmitted to the needle  10  and moves the needle forward in concert the wing-shaped handle. When the needle  10  reaches the destination cavity, the pressure within the needle will be changed by the pressure difference inside of the cavity, which in turn will change the pressure within the pressure chamber  22  of the clutching device. The pressure chamber  22  is in pressure communication with the needle  10 . If the destination cavity has a lower pressure than the pressure in the needle, this will result in a pressure drop within the pressure chamber  22 . On the other hand, if the destination cavity has a higher pressure than the pressure in the needle, the pressure chamber  22  will experience a pressure jump. This concomitant pressure change will in turn cause the pressure-sensing element  220  to change state, resulting in the disengagement of the force-receiving element  26  from the force sending element, thereby, disengaging the driving force. At this point, moving force applied to the wing-shaped handle will no longer be transmitted to the needle, thereby achieving the desired outcome of positioning the needle in the targeted location. 
         [0066]      FIG. 2  shows a perspective view of the exemplary connecting tube  20  for connecting a needle to a clutching device and a syringe. In this exemplary embodiment, the connecting tube has a first opening  201  for connecting to a needle, a second opening  202  for connecting to a clutching device, and a third opening  203  for connecting to a syringe. In this exemplary embodiment, the connecting tube is configured to have an inverted T-shape, wherein the horizontal portion of the inverted “T” brings the needle and the syringe into fluid communication and the vertical portion  20   a  of the “T” brings the clutching device into pressure communication with the needle and the syringe. The horizontal portion of the “T” may also include a depression  204  that serves as the force-sending element for interfacing and engaging with the force-receiving element  26  of the clutching device.  FIG. 3  shows another perspective view of the exemplary connecting tube  20 . 
         [0067]    Those skilled in the art will readily recognize that the size and shape of the openings  201  and  203  are to be adapted depending on the size and shape of the needle and syringe to be connected. In addition, it will also be recognized that the connecting tube is not limited to connecting only needles and syringes. It may also be used to connect, for example, an infusion pouch and an infusion tube. In such use cases, a clutching device may be used in conjunction with the connecting tube to indicate a change in pressure. It may also be coupled to a controller that regulates flow of infusion fluid. 
         [0068]      FIG. 4  shows a perspective view of a wing-shaped handle  24  together with the exemplary connecting tube  20  of  FIG. 1 . The wing-shaped handle  24  has a wing  240  for applying a force and a locking panel  242  connected thereto. The locking panel further include a locking hole  244  functioning as the force-sending element for interacting with the force-receiving element  26  of the clutching device. In this particular embodiment, the force-receiving element is a locking pin that protrudes through the locking hole  242  into the depression  204  on the connecting tube. When the force-receiving element  26  (the locking pin) is in this position, the wing-shaped handle  24  is locked to the entire needle-syringe assembly so that a driving force applied to the wing-shaped handle is transmitted to the needle and moves the needle in concert with the wing-shaped handle. 
         [0069]      FIG. 5  shows the same perspective view of  FIG. 4  with the addition of a see-through view of an exemplary positioning device. As shown in  FIG. 5 , the interior space of the body has a pressure chamber  22  that is connected to opening  202  of the connecting tube  20  via conduit  221  so that the pressure chamber  22  is placed in pressure communication with the needle. In this configuration, any pressure change within the needle will immediately be communicated to the pressure chamber  22  of the clutching device. 
         [0070]      FIG. 6  shows a sectional view of an exemplary clutching device  2  situated in a configuration as illustrated in  FIG. 5 . In this exemplary embodiment, a flexible film functions as the pressure-sensing element  220 . Connected to the film  220  is a locking pin  26  acting as the force-receiving element. When pressure in conduit  221  is greater than pressure in the pressure chamber  22 , the pressure-sensing element  220  assumes a concaved shape relative to the bottom of the clutching device. In this position, the locking pin  26  is pushed outwardly to form a protrusion on the bottom of the clutching device. 
         [0071]    In contrast, as shown in  FIG. 7 , when the pressure in the conduit  221  is lower than the pressure in the pressure chamber, the pressure-sensing element  220  will assume a convexed shape relative to the bottom of the clutching device. The force-receiving element  26 , being operatively connected to the pressure-sensing element  220 , is pulled up and receeds into the interior of the clutching device  2 . 
         [0072]      FIG. 8  shows a perspective view of an exemplary alternative embodiment of a syrigne-and-needle assembly in accordance with the present invention. In this exemplary embodiment, the clutching device has a tubular encasing shell  80  that encloses a connecting tube  20  and a toothed rail track  246  (shown in  FIG. 9 ). The connecting tube  20  has a first opening  201  adapted for connecting to a needle and a second opening  203  adapted for receiving a plunger  121 . In this exemplary embodiment, the plunger-receiving end is configured to have a sufficiently large size to function as a syringe. Thus, the connecting tube  20  is configured to have a connecting portion and a syringe portion  206  leading to the second opening  203 . For ease of discussion, the connecting tube  20  along with its syringe portion  206  and the plunger  121  may be referred to herein as the syringe-connecting tube assembly. 
         [0073]    During operation, the syringe-connecting tube assembly is designed to be movable within the encasing shell  80 . On the surface of the syringe portion  206 , there are provided wheel  207  and toothed wheel  208  to facilitate motion of the syringe-connecting tube assembly within the interior space of the clutching device. The encasing shell  80  may further include a force-applying handle  24  to facilitate handling of the assembly. 
         [0074]    The exemplary embodiment of  FIG. 8  is further illustrated in a cutaway view in  FIG. 9 . As illustrated in the figure, the interior wall of the positioning device  2  has a toothed rail track  246  for engaging the toothed wheal  208 . A force-receiving element  26  is operatively connected to pressure-sensing element  220  and supported by a pivot bar  209 . 
         [0075]    During operation, connecting tube  20  is connected to the needle and transmits the pressure in the needle to sensing element  220  located at opening  202  ( FIG. 20 -A). The pressure-sensing element  220  in this exemplary embodiment is a movable pin and the force-receiving element  26  is a hooked bar pivoted on a pivot bar  209 . The hooked bar has a first end  261  shaped like a hammer operatively connected to the sensing element  220  and a second end  262  shaped like a hook. When the pressure in the needle is above a threshold, the pressure sensing-element  26  (the movable pin) is pushed up against the first end  261  of the force interfacing element. This action causes the hook to be pivoted towards the surface of the syringe portion  206 , thereby, disengaging from the toothed rail track  246  to allow the syringe-connecting tube assembly to move forward. 
         [0076]    Referring to  FIG. 10 -B, when the pressure communicated to the pressure-sensing element drops below a threshold, the pressure-sensing element  220  will receed into the connecting tube, causing the first end  261  of the hooked bar to also drop toward the connecting tube. This action results in the hooked end  262  being pivoted towards the toothed rail track, thereby, engaging the toothed rail track to lock the syringe-needle assembly in place. 
         [0077]    As illustrated above, the pressure-sensing element, the force-receiving element and the force-sending element together define a driving force engaging mechanism that functions to engage and disengage a driving force form the needle depending on the external pressure encountered by the needle. Those skilled in the art will readily recognize that numerous alternative implementation of the driving force engaging mechanism is possible.  FIG. 11 -A and  FIG. 11 -B illustrates an exemplary alternative embodiment having a locking pin  26  operatively connected to a pressure-sensing element  220 . In this embodiment, the the locking pin  26  functions as the force-receiving element that engages and disengages the force-sending element, which in turn engages and disengages the syringe-needle assembly from the driving force. During operation of this embodiment, when the pressure in the connecting tube  20  is high, the pressure-sensing element will assume a convexing configuration (high pressure configuration) that pushes the locking pin  26  upward to engage the toothed rail track ( FIG. 11 -A). When the pressure in the connecting tube  20  is low, the pressure-sensing element will assume a flattened configuration (low pressure configuration) which in turn causes the locking pin to disengage from the toothed rail track, thereby, disengaging the needle-syringe assembly from the moving force ( FIG. 11 -B). 
         [0078]      FIG. 12 -A and  FIG. 12 -B illustrates another alternative embodiment that uses a toothed block as the force-receiving element  26  operatively connected to the pressure sensing element  220 . The toothed block in this exemplary embodiment has a toothed portion complementary to the rail track  246 . During operation of this embodiment, when the pressure in the connecting tube  20  is high, the pressure-sensing element  220  will assume a convexing configuration to push the toothed block  26  upward to engage the toothed rail track  246  ( FIG. 12 -A). When the pressure is low, the pressure-sensing element  220  will assume a flattened configuration so as to pull the toothed block  26  away from the toothed rail track  246 , thereby, disengaging the syringe-needle assembly from the driving force. 
         [0079]      FIG. 13 -A and  FIG. 13 -B illustrates yet another alternative embodiment. In this exemplary embodiment, the force-receiving element  26  has a upside-down “U”-shaped cross-section. It may be a hollow cylinder, or simply two vertical bars connected by a horizontal bar. Any geometric shape having an upside-down “U”-shaped cross-section may suitable be used. During operation of this embodiment, a high pressure in the connecting tube  20  will cause the pressure-sensing element  220  to assume a convexing configuration sufficient to lift the upside-down “U”-shaped force-receiving element  26  so as to disengage the force-sending element from the toothed rail track  246  ( FIG. 13 -A). When the pressure is low, the pressure-sensing element  220  will assume a flattened configuration which in turn lowers the upside-down “U”-shaped force-receiving element  26  to engage with the toothed rail track  246 . This action results in engagement of the driving force that moves the syringe-needle assembly. 
         [0080]    Those skilled in the art will recognize that unlike previously describe embodiments, this embodiment engages the driving force when the pressure experienced in the needle/connecting tube is low and disengages the moving force when the pressure in the need/connecting tube reaches above a threshold level. Thus, this exemplary embodiment illustrates how one may adapt the clutching device to work with use cases involving both positive and negative pressure differences. 
         [0081]      FIG. 14  shows a cutaway view of another exemplary embodiment of a clutching device. In this exemplary embodiment, the body of the clutching device  2  has an interior space  22  configured to accommodate a syringe-connecting tube assembly  12  mounted on a slidable frame  210 . The clutching device  2  further provides wing-shaped force-applying handles  24  for applying a moving force to the syringe-connecting tube assembly. Slotted sliding rails  300  are embeded in the body of the clutching device  2  for facilitating the sliding action of the syringe-connecting tube assembly within the interior space  22 . In this exemplary embodiment, the sliding handle is configured as an independently movable frame with a slotted spine  246  for engaging the syringe-connecting tube assembly. 
         [0082]      FIG. 15  shows a perspective view of the connecting tube  20  together with the syringe mounting frame  210 . The connecting tube  20  has a first opening  201  for connecting to a needle, a second opening  202  for communicating pressure in the connecting tube to a pressure-sensing element  202 , and a third opening  203  for connecting to a syringe. On the syringe mounting frame  210 , there are sliding plates  207  for engaging slotted sliding rails  300  within the interior space  22  of the clutching device  2 . 
         [0083]      FIG. 16  shows a cutaway view of the positioning device  2  with the wing-shaped moving handle  24  mounted in the slotted sliding rails  300 . When mounted, the moving handle  24  can be freely moved in the axial direction along the slotted rails by pushing on the wings  240  of the handle. A pressure-sensing element  220  with a force-receiving element operatively connected thereto is situated right below the slotted spine  246  of the moving handle  24 . During operation of this embodiment, the pressure in the connecting tube  20  is communicated to the pressure-sensing element  220  via opening  202 . A high pressure in the connecting tube  20  results in the pressure sensing element  220  adopting a convexing configuration (i.e. the high pressure configuration) that pushes the force-receiving element  26  (e.g. a locking pin) into a slot in the slotted spine  246  of the moving handle  24  ( FIG. 17 -A). In this configuration, the moving handle  24  and the syringe-connecting tube assembly are locked together so that the syringe-connecting tube assembly can be slided along the axial direction parallel to the slotted sliding rails  300  by pushing on the wings  240  of the moving handle  24 . When the pressure in the connecting tube drops below a threshold level, the pressure-sensing element  220  is made to adopt a flattened configuration (i.e. the low pressure configuration) that withdraws the force-receiving element  26  (e.g. a locking pin) from the slotted spine  246 . This configuration disengages the moving handle  24  from the syringe-connecting tube assembly so that any moving force applied to the moving handle will not be communicated to the syringe-connecting tube assembly ( FIG. 17 -B). 
         [0084]      FIG. 18  illustrates an exemplary preferred embodiment for a clutching device that requires only minimal modification to conventional epidural needles. In this embodiment, the clutching device is encased entirely in an enclosure  80 . The enclosure  80  has a first opening  201  for connecting to a needle, a second opening  202  for connecting to a syringe, and a pressure chamber that connects the first opening  201  and the second opening  202 . The pressure chamber is in pressure communication with a pressure sensing element  220 , which may be a flexible film. The pressure-sensing element  220  is operatively connected to a force-receiving element  26 . In a preferred embodiment, the force-receiving element is an inverted piston  26   a  with its rod pointing upwards. In some embodiments, the enclosure  80  has a throughhole from which the piston rod  26   a  may protrude to engage the locking panel  242  of the wing-shaped handle  24  via the locking hole  244 . In other embodiments, the enclosure  80  may have a slot for the locking panel  242 . In these embodiments, it is not necessary for the piston rod  26   a  to protrude through the enclosure  80 . 
         [0085]    To ensure the piston rod is initially in an “disengaged” position, a spring  26   b  may be fitted over the piston rod  26   a.  The spring  26   b  may be selected to set a threshold pressure at which the pressure-sensing element  220  is able to transition from a low pressure configuration to a high pressure configuration and vice versa. 
         [0086]      FIG. 19  shows an exemplary step-by-step process of positioning a needle in the epidural space using a needle-and-syringe assembly incorporating a clutching device as described above. In  FIG. 19 -A, a needle connected to a clutching device  2  outfitted with a wing-shaped handle  24  is first inserted into the ligament of a subject. At this stage, the pressure chamber is not yet pressurized so the piston rod  26   a  is in the “disengaged” position. Next, a syrigne is connected to the clutching device at opening  202 . As the plunger is pushed forward into the syringe, the pressure chamber becomes pressurized to push the piston rod  26   a  into the “engaged” position. Once the piston rod  26   a  is in the “engaged” position, any driving force applied to the wing-shaped handle  24  will be transmitted to the needle so that the needle may be advanced into the ligament by pushing on the wing-shaped handle  24  as shown in  FIG. 19 -B. 
         [0087]    Next, when the needle reaches the epidural space, the negative pressure within the epidural space causes the pressure chamber to depressurize. This change in pressure is immediately communicated to the pressure sensing element  220 , which causes the piston rod  26   a  to revert to the “disengaged” position ( FIG. 19 -C). Once the piston rod  26   a  is returned to the “disengaged” position, the wing-shaped handle  24  and the needle-syringe assembly are no longer coupled together. At this point, any force applied to the wing-shaped handle will only move the handle forward, resulting in the separation of the handle  24  from the positioning device  2  ( FIG. 19 -D). The needle is securely lodged in place by friction, achieving the desired result of automatically positioning the needle in the epidural space and locking it in place. 
         [0088]    In the above exemplary embodiments, one potential problem that may be encountered is that the piston rod  26   a  may not be disengaged easily due to the frictional force between the piston rod  26   a  and the locking panel  242  as illustrated in  FIG. 20 -A. This is referred to herein as the “stick pin” problem. 
         [0089]    One possible way to overcome the “sticky pin” problem is to use a material with small frictional coefficient. Another possible way to overcome the “sticky pin” problem is to use a stronger spring. However, a strong spring may pose another challenger in that the pressure in the needle may not be large enough to overcome the spring, a condition necessary to raise the piston rod  242  in order to engage the wing-shaped panel  24 . 
         [0090]      FIGS. 20 -B and  20 -C each illustrates an alternative embodiment that may obviate the “sticky pin” problem. In  FIG. 20 -B, there is shown an exemplary embodiment that utilizes a gear system to overcome the “sticky pin” problem. In this exemplary embodiment, a large gear for engaging the handle and a small gear for engaging the pin are bound together via a common shaft. By choosing the appropriate gear ratios, the friction between the pin and the gear can be accounted for so that the frictional force does not create a sticky pin situation. 
         [0091]    In  FIG. 20 -C, there is shown an exemplary embodiment that solves the “sticky pin” problem by positioning the inverted piston at an angle. During operation, as the user pushes the assembly forward, the piston is pushed upwards towards the chamber by the complementary pinhole. At the same time, the pressure in the chamber pushes the piston downwards towards the complementary pinhole. When the pressure in the chamber is high, the piston remains engaged with the complementary pinhole to hold the assembly in a “engaged” state. When the pressure in the chamer is relieved, the piston moves upwards to disengage from the complementary pinhole, thereby, placing the assembly into an “disengaged” state. By choosing an appropriate angle, the friction between the piston and the complementary pinhole can be taken into account so as to avoid a “sticky pin” situation. 
         [0092]    All features of each of the aspects of the present invention apply to all other aspects mutatis mutandis. Variations, modifications, and other implementations of what is described herein will occurr to those of ordinary skill in the art without departing from the spirit and the scope of the invention. Accordingly, the invention is to be defined not by the preceeding illustrative embodiments but instead by the spirit and scope of the following claims.