Patent Publication Number: US-8540679-B2

Title: Controlled detachment of intra-luminal medical device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior application Ser. No. 10/813,307, now U.S. Pat. No. 7,654,985, filed on Mar. 30, 2004, entitled “CONTROLLED DETACHMENT OF INTRA-LUMINAL MEDICAL DEVICE” which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to medical devices for temporary deployment in a body lumen and, more particularly, techniques for attachment and detachment of intra-luminal medical devices. 
     BACKGROUND 
     Gastroesophageal reflux occurs when stomach fluid, which typically includes stomach acids, intermittently flows from the stomach into the esophagus. It is common for most people to experience this fluid reflux occasionally as heartburn. Gastroesophageal reflux disease (GERD) is a clinical condition in which the reflux of stomach fluid into the esophagus is frequent enough and severe enough to impact a patient&#39;s normal functioning or to cause damage to the esophagus. 
     In the lower part of the esophagus, where the esophagus meets the stomach, there is a muscular valve called the lower esophageal sphincter (LES). Normally, the LES relaxes to allow food to enter into the stomach from the esophagus. The LES then contracts to prevent stomach fluids from entering the esophagus. In GERD, the LES relaxes too frequently or at inappropriate times, allowing stomach fluids to reflux into the esophagus. 
     The most common symptom of GERD is heartburn. Acid reflux may also lead to esophageal inflammation, which causes symptoms such as painful swallowing and difficulty swallowing. Pulmonary symptoms such as coughing, wheezing, asthma, or inflammation of the vocal cords or throat may occur in some patients. More serious complications from GERD include esophageal ulcers and narrowing of the esophagus. The most serious complication from chronic GERD is a condition called Barrett&#39;s esophagus in which the epithelium of the esophagus is replaced with abnormal tissue. Barrett&#39;s esophagus is a risk factor for the development of cancer of the esophagus. 
     Accurate diagnosis of GERD is difficult but important. Accurate diagnosis allows identification of individuals at high risk for developing the complications associated with GERD. It is also important to be able to differentiate between gastroesophageal reflux, other gastrointestinal conditions, and various cardiac conditions. For example, the similarity between the symptoms of a heart attack and heartburn often lead to confusion about the cause of the symptoms. 
     Esophageal manometry, esophageal endoscopy, and esophageal pH monitoring are standard methods of measuring esophageal exposure to stomach acids and are currently used to diagnose GERD. A variety of endoscopic devices have been designed to monitor various parameters within the esophagus. Many devices require an indwelling catheter to maintain a sensor in place within the esophagus. The catheter protrudes from the patient&#39;s nasal or oral passage, however, causing discomfort and ordinarily requiring in-patient supervision. 
     The Bravo™ pH monitoring system, commercially available from Medtronic, Inc., of Minneapolis, Minn., is an example of a system useful in diagnosing esophageal reflux without the need for a catheter. The Bravo system includes an intra-luminal capsule that is temporarily placed within the esophagus via an endoscopic delivery device. The capsule has a vacuum cavity that captures a portion of the esophageal mucosal tissue. A physician then advances a pin through the captured tissue to secure the capsule relative to the esophageal wall. The capsule causes little discomfort and permits the patient to ambulate. Eventually, the capture tissue sloughs away and releases the capsule, which then passes through the patient&#39;s gastrointestinal tract for eventual discharge. 
     Table 1 below lists documents that disclose various techniques for diagnosing or detecting GERD, and other documents that disclose techniques for measuring conditions within the esophagus. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Pat. No. 
                 Inventors 
                 Title 
               
               
                   
               
             
            
               
                 5,833,625 
                 Essen-Moller 
                 Ambulatory Reflux Monitoring  
               
               
                   
                   
                 System 
               
               
                 5,967,986 
                 Cimochowski et al. 
                 Endoluminal Implant with  
               
               
                   
                   
                 Fluid Flow Sensing Capability 
               
               
                 6,285,897 
                 Kilcoyne et al. 
                 Remote Physiological  
               
               
                   
                   
                 Monitoring System 
               
               
                 6,689,056 
                 Kilcoyne et al. 
                 Implantable Monitoring Probe 
               
               
                 US20020103424 
                 Swoyer et al. 
                 Implantable medical device  
               
               
                   
                   
                 affixed internally within the  
               
               
                   
                   
                 gastrointestinal tract 
               
               
                   
               
            
           
         
       
     
     All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention. 
     SUMMARY OF THE INVENTION 
     In general, the invention is directed to techniques for controlled detachment of intra-luminal medical devices such as capsule-like devices carrying sensors, electrical stimulators, therapeutic substances, or the like. A medical device in accordance with the invention incorporates a controlled detachment mechanism to selectively detach a medical device from a tissue attachment site within a body lumen. 
     Various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to prior devices for intra-luminal sensing and stimulation. These problems include the inability of existing intra-luminal medical devices to be selectively detached when desired. Intra-luminal medical devices such as capsules generally do not permit on-demand detachment without endoscopic or surgical intervention. On the contrary, detachment typically occurs when tissue at the attachment site sloughs away, or when degradable attachment material carried by the medical device is sufficiently degraded. Consequently, the time of detachment, and hence the duration of attachment, can be uncertain. In particular, an intra-luminal medical device may reside at the attachment site for an undesirably long period of time. For example, a medical device may acquire sufficient data or deliver a sufficient course of therapy, yet still remain in place for a prolonged period of time. In some cases, removal of the medical device may require endoscopic or surgical intervention. In other cases, an intra-luminal medical device may release too quickly due to differences in tissue integrity or other attachment conditions, preventing a sufficient amount of time for monitoring or therapy. 
     Various embodiments of the present invention are capable of solving at least one of the foregoing problems. When embodied in a device for intra-luminal monitoring or stimulation, for example, the invention includes a variety of features that facilitate the controlled detachment of such a device without the need for endoscopic or surgical intervention. In particular, the invention provides features that permit self-detachment of an intra-luminal device. Detachment may occur at a desired time in response to a control signal, and need not rely on tissue integrity or other attachment conditions. The control signal may be generated on-demand by a user or automatically in response to expiration of a timer or upon performance of a sufficient course of monitoring or stimulation. In this manner, the invention incorporates features that permit an intra-luminal medical device to be placed within a body lumen for a controllable amount of time for monitoring, therapy, or both. Accordingly, a medical device configured in accordance with the invention may eliminate one or more of the problems that can result from uncertain and inconsistent detachment of intra-luminal medical devices 
     Various embodiments of the invention may possess one or more features to solve the aforementioned problems in the existing art. In some embodiments, a medical device for placement within a body lumen of a patient comprises a device housing, a fixation mechanism and a detachment mechanism. The device housing is sized for introduction into the body lumen. The fixation mechanism attaches the device housing to a surface within the body lumen. The detachment mechanism detaches the device housing from the surface of the body lumen. The detachment mechanism may be responsive to a control signal to detach the medical device from a tissue site. 
     As an example, an intra-luminal device may be equipped with a fixation mechanism having a spring-loaded shaft to capture tissue at an attachment site. In this example, the spring bias forces the shaft toward the tissue, e.g., to pinch or penetrate the tissue. However, an actuator, such as an electromagnetic device, is provided to selectively drive the shaft against the spring bias and thereby release the tissue. Examples of a suitable electromagnetic device include a solenoid coil. 
     As an alternative, the spring bias may force the shaft away from the tissue. In this case, a piezoelectric element or other actuator may be provided with a detent that abuts one end of the shaft, and holds the shaft against the spring bias to engage the tissue. Upon activation of the piezoelectric element, the detent clears the shaft, permitting the shaft to release the tissue. 
     As a further example, the shaft may include a fuse link that is electrically blowable to sever the shaft. Upon activation of a current source to drive current through the shaft, the link disintegrates and permits the capsule to release from the tissue. 
     As an added example, the fixation mechanism may include a bonding agent that bonds the medical device to the tissue site. The bonding agent may be biodegradable or rapidly degradable in the presence of a degradation agent, permitting detachment of the medical device upon application of the degradation agent to the tissue site. 
     In comparison to known techniques for electrical stimulation of the gastrointestinal tract, various embodiments of the invention may provide one or more advantages. For example, the invention permits self-detachment of an intra-luminal medical device at a desired time. In this manner, the invention supports on-demand or timed detachment of an intra-luminal medical device without the need for endoscopic or surgical intervention. Consequently, the time of detachment can be controlled, providing greater certainty about the duration of attachment, and hence the duration of monitoring or therapy within the body lumen. The invention thereby eliminates prolonged attachment of an intra-luminal medical device for a long period of time beyond a desired monitoring or therapy duration. Thus, if desired, the medical device may be detached immediately following acquisition of a sufficient amount of a data, or delivery of a sufficient course of therapy. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an intra-luminal medical device system shown in conjunction with a patient. 
         FIG. 2  is a functional block diagram illustrating exemplary components of an intra-luminal medical device. 
         FIG. 3  is a cross-sectional side view of an intra-luminal medical device with a detachment mechanism in accordance with an embodiment of the invention. 
         FIG. 4  is a cross-sectional side view of the medical device of  FIG. 3  upon application of vacuum pressure to draw luminal tissue into the device. 
         FIG. 5  is a cross-sectional side view of the medical device of  FIG. 3  upon actuation of a shaft to capture luminal tissue. 
         FIG. 6  is a schematic diagram illustrating deployment of the medical device of  FIG. 3  within a patient&#39;s gastrointestinal tract. 
         FIG. 7  is a cross-sectional side view illustrating positioning of the medical device of  FIG. 3  with an endoscopic delivery device. 
         FIG. 8  is a cross-sectional side view of a medical device with a detachment mechanism including a fuse link in accordance with another embodiment of the invention. 
         FIG. 9  is a cross-sectional side view of the medical device of  FIG. 8  after the fuse link is blown by electrical current. 
         FIG. 10  is a cross-sectional side view of a medical device with a detachment mechanism including a detent actuated by a piezoelectric element in accordance with another embodiment of the invention. 
         FIG. 11  is a cross-sectional side view of the medical device of  FIG. 10  upon release of the detent. 
         FIG. 12  is a flow diagram illustrating a method for attaching and detaching an intra-luminal medical device in accordance with an embodiment of the invention. 
         FIG. 13  is another flow diagram illustrating a method for attaching and detaching an intra-luminal medical device in accordance with another embodiment of the invention. 
         FIG. 14  is a cross-sectional side view of an endoscopic delivery device for forming a bonding agent to attach an intra-luminal medical device in accordance with an embodiment of the invention. 
         FIG. 15  is a cross-sectional side view of the endoscopic delivery device following attachment of the medical device with the bonding agent. 
         FIG. 16  is a side view of the medical device of  FIGS. 14 and 15  following withdrawal of the endoscopic delivery device. 
         FIG. 17  is a cross-sectional end view of a body lumen in which the medical device of  FIGS. 14-16  is implanted. 
         FIG. 18  is a flow diagram illustrating attachment and detachment of an intra-luminal medical device with a bonding agent and a degradation agent in accordance with an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic diagram illustrating an intra-luminal medical device system  10  shown in conjunction with a patient  12 . System  10  may be configured to monitor physiological conditions or deliver electrical stimulation at a target location within a body lumen such as the gastrointestinal tract, e.g., within esophagus  14 , stomach  16 , small intestine  18 , or the colon (not shown). System  10  includes an implanted intra-luminal medical device  20 , which may be placed at the target location by endoscopic delivery. As will be described, medical device  20  includes a fixation mechanism to attach the medical device to a target tissue site, as well as a detachment mechanism that permits selective detachment of the medical device on a controlled basis. In this manner, the duration of attachment of medical device  20 , and its time of release, can be controlled by medical personnel or patient  12 . 
     Medical device  20  may be delivered via the oral or nasal passage of patient  12  using an endoscopic delivery device. In the example of  FIG. 1 , medical device  20  resides within esophagus  14 . In this case, the endoscopic delivery device traverses esophagus  14  and then places medical device above lower esophageal sphincter (LES)  22  of patient  12 , e.g., for monitoring of physiological conditions such as pressure, fluid flow, pH, or temperature to diagnose GERD. Alternatively, medical device  20  may deliver an electrical stimulation waveform to treat a variety of symptoms such as nausea, vomiting and gastric discomfort, particularly when the medical device is placed within stomach  18 . In other embodiments, medical device  20  may combine both monitoring and stimulation functions. Also, medical device  20  may deliver other types of therapy in some embodiments. 
     Medical device  20  may have a capsule-like device housing sized for endoscopic introduction via esophagus  14  and, in some embodiments, passage through the gastrointestinal tract. For example, the capsule-like device housing of medical device  20  may have a maximum length of less than approximately 10 mm and a maximum width of less than approximately 5 mm. In some embodiments, the capsule-like device housing may be substantially cylindrical, with a length greater than its diameter and flat or rounded ends, although the invention is not limited to any particular shape. For a cylindrical device housing, medical device  20  may have a maximum height of less than approximately 10 mm and a maximum diameter of less than approximately 5 mm. The device housing may be formed from a variety of biocompatible materials such as stainless steel or titanium. 
     The capsule-like device housing of medical device  20  further includes a power source, a pulse generator, one or more electrodes, a fixation mechanism, and a detachment mechanism, if configured for electrical stimulation. If configured for monitoring, the capsule-like housing of medical device  20  may include a power source, a sensor, signal processing electronics, a fixation mechanism, and a detachment mechanism. Although medical device  20  may be configured for monitoring, delivery of electrical stimulation, or both, the medical device will be generally described herein in the context of monitoring. 
     The fixation mechanism secures medical device  20  to a target location within a body lumen such as the gastrointestinal tract. In particular, the fixation mechanism may perforate the mucosa and lodge in the muscularis externa of the gastrointestinal tract wall when introduced against the mucosa, or grip a fold of the mucosa. To place medical device  20  for gastrointestinal applications, a distal end of the endoscopic delivery device is inserted into esophagus  14  and guided to a target location within the gastrointestinal tract. 
     Following placement of medical device  20 , the endoscopic delivery device is withdrawn from patient  12  once the medical device is attached to a target site. Hence, surgery is not required to place medical device  20  within patient  12 . Moreover, following placement of medical device  20 , there are no leads or other connections that extend outside of patient  12 . On the contrary, medical device  20  may be entirely self-contained, self-powered and integrated within a common, capsule-like housing. In some embodiments, an external source of inductively coupled power may be used to power some features of medical device  20 , such as the detachment mechanism. 
     The fixation mechanism may take a variety of forms, and may include a variety of features such as one or more shafts, hooks, barbs, screws, sutures, clips, pincers, staples, tacks, or other fasteners. In some embodiments, the fixation mechanism can at least partially penetrate the mucosal lining of the gastrointestinal tract. In other embodiments, the fixation mechanism pinches or otherwise holds a fold of mucosal lining tissue. In either case, the fixation mechanism securely attaches medical device  10  to the target location, subject to detachment by a controlled detachment mechanism as further described herein. Examples of suitable biocompatible materials for fabrication of the fixation mechanism include stainless steel, titanium, polyethylene, nylon, PTFE, nitinol, or the like. 
     In some embodiments, the fixation mechanism may be made from a degradable material that degrades or absorbs over time at the attachment site to release medical device  20  from tissue at the target location. In either case, upon detachment, medical device  20  passes through the gastrointestinal tract of patient  12 . U.S. Pat. Nos. 6,285,897 and 6,698,056 to Kilcoyne et al. provide examples of fixation mechanisms for attaching monitoring devices to the lining of the esophagus, including suitable degradable materials. The fixation mechanisms described in the Kilcoyne patents may be suitable for attachment of medical device  20 . The contents of the Kilcoyne et al. patents are incorporated herein by reference in their entireties. 
     Examples of suitable degradable materials for fabrication of the fixation mechanism or structures include bioabsorbable or dissolvable materials such as polylactic acid (PLA) or copolymers of PLA and glycolic acid, or polymers of p-dioxanone and 1,4-dioxepan-2-one, as described in the Kilcoyne patents. A variety of absorbable polyesters of hydroxycarboxylic acids may be used, such as polylactide, polyglycolide, and copolymers of lactide and glycolide, as also described in the Kilcoyne patents. Other examples of degradable materials include polyether ketone (PEEK), carbohydrates or fibrin. 
     Alternatively, the fixation mechanism may include or take the form of a bonding agent such as a surgical adhesive that supplements the attachment made by the fixation mechanism or serves as the fixation mechanism itself. In other words, a pin, hook or other fixation mechanism may be accompanied by a bonding agent such as a biocompatible adhesive, or the adhesive may be used as the sole fixation mechanism without mechanical fasteners. Hence, the bonding agent may work alone or in combination with a mechanical fastener to form a fixation mechanism. 
     Examples of suitable boding agents for bonding the medical device  10  to the mucosal lining include surgical adhesive ssuch as any of a variety of cyanoacrylates, derivatives of cyanoacrylates, or any other adhesive compound with acceptable toxicity to human intra-luminal cells that provides the necessary adhesion properties required to secure medical device  20  to the target location for a period of time sufficient for monitoring or delivery of electrical stimulation or other therapies. Adhesives may be injected or otherwise applied into the region surrounding the target location, e.g., via one or more delivery channels within the endoscopic delivery device, or carried by the medical device  20  itself. 
     Other examples of suitable bonding agents include biologically mediated bonding agents such as fibrin glues. Fibrin glue is a biological tissue adhesive found to be an effective sealant and topical hemostatic agent. An example of a commercially available fibrin glue is marketed as Tissucol. Fibrin glue generally includes concentrated fibrinogen and factor XII combined with thrombin and calcium to form a coagulum. This preparation stimulates the final stage of the clotting cascade, producing a fibrin clot from fibrinogen in the presence of calcium within seconds after administration of the thrombin-activating solution. Other biologically mediated bonding agents that may be suitable include glues based on collagen, albumin or gelatin. 
     A detachment mechanism is configured to permit medical device  20  to self-detach from the target location, i.e., without the need for endocscopic intervention. Upon detachment, for gastrointestinal applications, medical device  20  is free to pass through the gastrointestinal tract for excretion by the patient  12 . In other body lumens, medical device  20  may pass with other bodily fluids or masses, or be retrieved by an endoscopic retrieval device. In each case, rather than waiting for the attachment mechanism to detach from the target tissue site, e.g., due to sloughing of tissue or slow degradation of the attachment mechanism, the detachment mechanism permits rapid and controlled detachment, either by electrical mechanical actuation, electrical destruction, rapid degradation of the fixation mechanism, or other controllable processes. The detachment mechanism will be described in greater detail below. 
     As further shown in  FIG. 1 , in some embodiments, medical device  20  may communicate with an external controller  24  via wireless telemetry. Controller  24  may permit a user to retrieve physiological information obtained by a sensor carried by medical device  20 . Alternatively, in other embodiments, controller  24  may be used to activate, deactivate and adjust stimulation parameters applied by an electrical stimulator carried by medical device  20 . For example, a patient  12  or other user may use controller  24  to start stimulation, stop stimulation, set stimulation duration, or adjust stimulation amplitude, frequency, pulse width and duty cycle. In addition, external controller  24  may permit a patient  12  or other user to activate the detachment mechanism within medical device  20 , and thereby selectively release the medical device from the target tissue site. 
     Wireless telemetry may be accomplished by radio frequency communication or proximal inductive interaction of controller  24  with medical device  20 . In some embodiments, telemetry for purposes of controlling the detachment mechanism may be accomplished by simply passing a magnet over medical device  20  or inductively powering the medical device via an inductive coil interface. External controller  24  may take the form of a portable, handheld device, like a pager or cell phone, that can be carried by patient  12 . External controller  24  may include an antenna that is attached to the body of patient  12  at a location proximate to the location of medical device  20  to improve wireless communication reliability. Also, in some embodiments, controller  24  may receive operational or status information from medical device  20 , and may be configured to actively interrogate the medical device to receive the information. 
       FIG. 2  is a block diagram illustrating exemplary functional components of intra-luminal medical device  20 . In the example of  FIG. 2 , medical device  20  may include a controller  26 , memory  28 , sensor circuitry  30 , telemetry module  32 , battery power source  34 , driver circuitry  36  and detachment mechanism  38 . An optional stimulator  31  is further shown in  FIG. 2 . In some embodiments, medical device  20  may further include an inductive power interface  39  to power driver circuitry  36  and thereby actuate detachment mechanism  38 . In other embodiments, driver circuitry  36  may be powered by battery power source  34 . Telemetry module  32  permits communication with external controller  24  for transfer of data. In stimulation embodiments, telemetry module  32  may be optional. For example, a medical device  20  may exclude telemetry module  32  if all operating parameters are preset and fixed within the device, or if data is to be acquired from the medical device after passage through the gastrointestinal tract. Exclusion of telemetry module  32  may be desirable in some applications to achieve reductions in the size of medical device  20 . 
     Controller  26  controls operation of medical device  20  and may include one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other equivalent logic circuitry. Memory  28  may include any magnetic, electronic, or optical media, such as random access memory (RAM), read-only memory (ROM), electronically-erasable programmable ROM (EEPROM), flash memory, or the like. Memory  28  may store program instructions that, when executed by controller  26 , cause the controller to perform the functions ascribed to it herein. For example, memory  28  may store instructions for controller  26  to execute in support of control of telemetry module  32 , sensor circuitry  30  and driver circuitry  36 . 
     Telemetry module  32  may include a transmitter and receiver to permit bi-directional communication between medical device  20  and external controller  24 . In this manner, external controller  24  may transmit commands to medical device  20  and receive status and operational information from the medical device. Telemetry module  32  includes an antenna, which may take a variety of forms. For example, the antenna may be formed by a conductive coil or wire embedded in a housing associated with medical device  20 . Alternatively, the antenna may be mounted on a circuit board carrying other components of medical device  20 , or take the form of a circuit trace on the circuit board. If medical device  20  does not include a telemetry module  32 , a magnetic reed switch may be provided in a circuit so that medical device  20 , with the aid of an external magnet, may activate itself or driver circuitry  36  and detachment mechanism  38  in response to external input. 
     Battery power source  34  may take the form of a battery and power circuitry. Medical device  20  typically may be used for a few days or weeks, and therefore may not require substantial battery resources. Accordingly, the battery within battery power source  34  may be very small. An example of a suitable battery is a model  317  silver oxide battery often used to power watches. The model  317  battery has voltage of 1.55 volts and a capacity of 12.5 mA-hours and has a disk-like shape with a diameter of approximately 5.7 mm and a thickness of approximately 1.65 mm. With a typical range of power requirements, the model  317  battery can be expected to power medical device  20  for between approximately two weeks and eighteen months, depending on actual usage conditions. 
     Different types of batteries or different battery sizes may be used, depending on the requirements of a given application. In further embodiments, battery power source  34  may be rechargeable via induction or ultrasonic energy transmission, and includes an appropriate circuit for recovering transcutaneously received energy. For example, battery power source  34  may include a secondary coil and a rectifier circuit for inductive energy transfer. In still other embodiments, battery power source  34  may not include any storage element, and medical device  20  may be fully powered via transcutaneous inductive energy transfer. 
     If provided, stimulator  31  incorporates a pulse generator that produces an electrical stimulation waveform with parameters selected to suppress selected symptoms, such as nausea and vomiting. Stimulator  31  may further include a charging circuit, an energy storage device to store stimulation energy, and a stimulation interface including electrodes. As an example, the pulse generator of stimulator  31  may incorporate circuitry similar to the pulse generation circuitry in the ITREL 3 neurostimulator, commercially available from Medtronic, Inc. of Minneapolis, Minn. The structure and function of stimulator  31  may generally conform to that described in commonly owned and co-pending U.S. application Ser. No. 10/801,230, to Timothy Herbert and Warren Starkebaum, filed Mar. 16, 2004, and bearing the entire content of which is incorporated herein by reference. 
       FIG. 3  is a cross-sectional side view of an intra-luminal medical device  20 A with a detachment mechanism in accordance with an embodiment of the invention. In the example of  FIG. 3 , medical device  20 A is placed adjacent mucosal lining  40  within esophagus  14 . A shaft  42  extends through an internal passage  44  in the capsule-like housing of medical device  20 A. Medical device  20 A defines a vacuum cavity  46  on a side of the housing adjacent mucosal lining  40 . A vacuum port  48  applies vacuum pressure to vacuum cavity  46  to draw mucosal tissue into the cavity. Vacuum port  48  is attached to a vacuum line (not shown) carried by an endoscopic delivery device. A coupling member  50  is attached to a proximal end of shaft  42 . An elongated control rod (not shown in  FIG. 3 ) is mounted to coupling member  50  to hold shaft  42  in place against a mechanical bias applied by a spring  52 . The elongated control rod and coupling member  50  may be coupled to one another by a threaded engagement. As will be described in further detail below, controller  26 , solenoid coil  58 , current source  60 , and switch  62  form part of a controlled detachment mechanism. 
       FIG. 4  is a cross-sectional side view of the medical device  20 A of  FIG. 3  upon application of vacuum pressure via vacuum line  48  to draw mucosal tissue  64  into vacuum cavity  46  in the device.  FIG. 5  is a cross-sectional side view of medical device  20 A of  FIG. 3  upon actuation of shaft  42  to capture mucosal tissue  64 . Spring  52  is coupled at a first end  54  to medical device  20  and at a second end  56  to shaft  42 . Upon release of coupling member  50  by the elongated control rod, shaft  42  extends into vacuum cavity  46  under the spring bias created by spring  52 . Spring  52  biases shaft  42  against mucosal tissue  64  drawn into vacuum cavity  46  under vacuum pressure. In this manner, shaft  42  pinches mucosal tissue  64  within vacuum cavity  46 , and thereby attaches medical device  20 A to the mucosal lining. In other embodiments, shaft  42  may partially or completely penetrate mucosal tissue  64 , and may have a sharpened tip to facilitate penetration. Vacuum pressure is then terminated, and the endoscopic delivery device is withdrawn from the esophagus, leaving medical device  20 A in place. 
     In the example of  FIGS. 3-5 , shaft  42 , vacuum cavity  46  and spring  52  together form a fixation mechanism that attaches medical device  20 A to mucosal tissue  64  at a target site within the gastrointestinal tract. With further reference to the embodiment depicted in  FIGS. 3-5 , controller  26 , solenoid coil  58 , current source  60 , and switch  62  form parts of a controlled detachment mechanism. In particular, current source  60  may form part of driver circuitry  36  ( FIG. 2 ) to drive the detachment mechanism. Although medical device  20 A could eventually detach from mucosal lining  40  due to sloughing of the tissue  64  held by shaft  42 , controlled detachment is preferred so that the time of detachment, and hence the duration of implantation of the medical device within the gastrointestinal tract, can be controlled with greater certainty. 
     In operation, upon receipt of a control signal, controller  26  activates switch  62  to turn current source  60  “ON” and thereby drive current across solenoid coil  58 . For this arrangement, shaft  42  is formed from a ferromagnetic material to magnetically interact with solenoid coil  58 . Current source  60  energizes solenoid coil  58  to create a magnetic field sufficient to magnetically actuate shaft  42 . In particular, solenoid coil  58  causes shaft  42  to overcome the spring bias created by spring  52  and then retract into passage  44 , thereby releasing the portion of mucosal tissue  64  held within vacuum cavity  46 . Once the mucosal tissue  64  is released by shaft  42 , medical device  20 A detaches from mucosal lining  40  for passage through the gastrointestinal tract. 
     Current source  60  may derive operating power from battery power source  34  ( FIG. 2 ). Although a substantial amount of current may be required to overcome the spring bias of spring  52 , the detachment mechanism only needs to be used once, i.e., at the time of detachment. Hence, battery power source  34  may be selected to provide sufficient power given the operating requirements of medical device  20 A for monitoring or stimulation and the spring bias created by spring  52 . 
     Alternatively, in some embodiments, inductive power interface  39  may be used to provide sufficient power to drive detachment mechanism  38  ( FIG. 2 ). For example, inductive power interface  39  ( FIG. 2 ) may be dedicated to generation of power by inductive coupling with an external source of inductive power for the purpose of driving the detachment mechanism. Inductive power interface  39  may include an inductive coil within the housing of medical device  20 A for transcutaneous transfer of power from an external source. 
     In some embodiments, controller  26  may not be needed to drive the detachment mechanism. Instead, current source  60  may be responsive to the presence of power on a power rail due to inductive coupling of power via inductive power interface  39 . In this case, power normally is not supplied to current source  60 , and is only available when a patient  12  or other user presents an external power source in close proximity to inductive power interface  39  to thereby release medical device  20 A. 
     In the examples above, the detachment mechanism may be responsive to a control signal in the form of a signal transmitted to controller  26  via telemetry module  32 , or a control signal in the form of power delivered to medical device via inductive power interface  39 . As a further alternative, controller  26  may be responsive to a clock carried by medical device  20 A. The clock tracks a period of time from the time of deployment or activation of medical device  20 A to a desired time of detachment. When the time of detachment is reached, controller  26  responds to the clock by activating the detachment mechanism. In other embodiments, controller  26  may activate the detachment mechanism when a sufficient amount of data has been obtained, or a sufficient amount of stimulation has been provided. 
       FIG. 6  is a schematic diagram illustrating deployment of a medical device  20  within a patient&#39;s gastrointestinal tract. As shown in  FIG. 6 , an endoscopic delivery device  66  serves to position and place medical device  20  within the gastrointestinal tract of patient  12 . Delivery device  66  includes a proximal portion, referred to herein as a handle  68 , and a flexible probe  70  that extends from handle  68  into the gastrointestinal tract of patient  12 . Medical device  20 A is coupled to a distal end  72  of delivery device  66  for delivery to a target location within the gastrointestinal tract. Distal end  72  of delivery device  66  enters esophagus  14 , via either nasal cavity  74  or oral cavity  76 , and extends into esophagus  14  to a desired placement location. Medical device  20 A is attached to the mucosal lining at a target location within esophagus  14 , stomach  16 , or small intestine  18 , and the distal end  72  of delivery device  66  releases medical device  20 A. 
       FIG. 7  is a cross-sectional side view illustrating positioning of medical device  20 A of  FIG. 3  with an endoscopic delivery device  66 . As shown in  FIG. 7 , medical device  20 A is held within a placement bay  79  within distal end  72  of endoscopic delivery device  66 . In this example, an elongated control rod  78  includes a threaded member  80  that engages a reciprocally threaded bore within coupling member  50 . Other types of coupling engagements may be used to attach elongated control rod  78  to coupling member  50 . 
     In general, elongated control rod  78  permits a physician to exert force to maintain shaft  42  in a retracted position relative to vacuum cavity  46 , despite the spring bias exerted in the opposite direction by spring  52 . Elongated control rod  78  is flexible and extends though flexible probe  70  to handle  68  ( FIG. 6 ) so that the physician can manipulate the elongated control rod. In particular, the physician may rotate elongated control rod  78  to withdraw the elongated control rod from threaded engagement with coupling member  50  and thereby release shaft  42  to extend into vacuum cavity  46  under spring bias supplied by spring  52 . 
     Before releasing shaft  42 , however, the physician activates vacuum line  82  to supply vacuum pressure to vacuum port  48  of medical device  20 A. The vacuum pressure is applied to vacuum cavity  46  to draw mucosal tissue  64  into the vacuum cavity. Upon release of shaft  42 , mucosal tissue  64  is held securely within vacuum cavity, thereby securely attaching medical device  20 A to mucosal lining  40  at the desired target tissue location. The spring bias from spring  52  maintains the position of shaft  42 , so that the shaft effectively pinches the mucosal tissue  64 . 
       FIG. 8  is a cross-sectional side view of an alternative medical device  20 B with a detachment mechanism including a fuse link  92  in accordance with another embodiment of the invention. Medical device  20 B generally conforms to medical device  20 A of  FIGS. 3-5  and  7 . For example, medical device  20 B of  FIG. 8  includes passage  44 , vacuum cavity  46 , vacuum port  48 . However, passage  44  contains a pin-like shaft  84  with a coupling member  86  and a sharpened tip  88 . A physician advances an elongated control rod (not shown in  FIG. 8 ) within an endoscopic delivery device to drive shaft  84  into and through mucosal tissue  64  captured within vacuum cavity  46  upon application of vacuum pressure. Sharpened tip  88  penetrates tissue  64  and resides in a recess  90  defined by medical device  20 B. In this manner, shaft  84  securely retains mucosal tissue  64  within vacuum cavity  46 , and thereby attaches medical device  20 B to mucosal lining  50 . In other embodiments, shaft  84  may be configured to pinch, rather than penetrate, mucosal tissue  64 . 
     To selectively detach medical device  20 B from mucosal lining  40  in a controlled manner, medical device  20 B includes a detachment mechanism. The detachment mechanism includes controller  26 , current source  60 , switch  62 , fuse link  92 , and contact terminals  94  and  96 . In response to a control signal, controller  26  activates switch  62  to apply current from current source  60  across contact terminals  94 ,  96 . Again, the control signal may be delivered by an external controller, delivered in the form of power inductively transferred to the medical device  20 B, or be generated in response to a clock carried by the medical device. Contact terminals  94 ,  96  may take the form of conductive rails, posts, brushes, or the like, which make electrical contact with shaft  84 . In some embodiments, contact terminals  94 ,  96  may be substantially annular and extend about the circumference of shaft  84 . 
     Shaft  84  is constructed from an electrically conductive material so that current applied across contact terminals  94 ,  96  is likewise applied across fuse link  92 . Fuse link  92  may be constructed from any of a variety of materials that are easily degraded upon application of a sufficient level of electrical current. The fuse materials may be vaporized or melted. Example materials include nickel/chromium (nichrome), zinc/copper, or silver/copper alloys which are commonly used in fuse applications. Other possible fuse materials include polysilicon or conductive polymers or materials that contain carbon black. As further examples, a material in combination with an embedded conductive/resistive material may be used as fuse material. The embedded conductive/resistive material may be a conductive wire filament. When the wire filament heats, the surrounding material melts, causing the link to lose its mechanical strength such that the capsule dislodges from the tissue site. For example, a fuse material made of a plastic or polymer may dissolve, break, change elasticity, or otherwise change state when heat is generated by current flowing through the embedded wire filament. A fuse material can be formed as an integral part of shaft  84  with conductive proximal and distal shaft portions by molding, casting, welding, soldering or the like. 
     The electrical current from current source  60  has an amplitude level sufficient to “blow” fuse link  92 , so that shaft  84  breaks apart into two or more pieces. As an example, a current level on the order of approximately 1 milliamps to approximately 500 milliamps should be sufficient to blow fuse link  92 , although sufficient current levels will vary as a function of the material selected and the resistance of the material. In some embodiments, higher current levels up to approximately 20 amps may be produced for some materials.  FIG. 9  is a cross-sectional side view of the medical device  20 B of  FIG. 8  after fuse link  92  is blown by electrical current. Once fuse link  92  is blown, medical device  20 B is free to release from tissue  64 . A distal portion of shaft  84  may remain in tissue  64 , but eventually pass through the system of the patient as the tissue sloughs away over time. 
     Again, as in other embodiments, the current supplied by current source  60  may be derived from a battery power source that supplies power from a battery carried by medical device  20 B, or an inductive power source that receives inductively coupled power from a power source external to the patient. Battery power may be sufficient, particularly because the level of current sufficient to blow fuse link  92  only needs to be applied once during the operational life of medical device  20 B. 
       FIG. 10  is a cross-sectional side view of a medical device  20 C with a detachment mechanism including a detent  104  actuated by a piezoelectric element  106  in accordance with another embodiment of the invention. Like medical device  20 A of  FIGS. 3-5  and  7 , medical device  20 C includes a shaft  98  and a spring  100  that biases the shaft. However, spring  100  is configured to bias shaft  98  away from vacuum cavity  46  such that the shaft is retracted into passage  44 . A detent  106  attached to a piezoelectric element  104  abuts a proximal end of shaft  98  adjacent coupling member  102 , and prevents shaft  98  from retracting fully into passage  44 . 
     During deployment, shaft  98  may be fully retracted into passage  44 , such that coupling member  102  resides on a side of piezoelectric element  104  opposite spring  100 . To attach medical device  20 C to mucosal lining  40 , a physician advances shaft  98  toward vacuum cavity  46  using an elongated control rod in the endoscopic delivery device. Upon advancement of shaft  98 , coupling member  102  clears detent  106  which includes a ramped surface to facilitate clearance. 
     Detent  106  may be spring-loaded such that shaft  98  urges the detent outward as the shaft passes. Once coupling member  102  clears detent  106 , the detent moves inward, e.g., under spring bias, to abut coupling member  102  and lock shaft  98  against movement away from vacuum cavity  46 . In this manner, shaft  98  engages mucosal tissue  64  and is locked into place to secure medical device  20 C against movement and thereby attach the medical device to mucosal lining  40 . 
     In this embodiment, the detachment mechanism includes controller  26 , current source  60 , switch  62 , and piezoelectric element  104 . In response to a control signal, controller  26  activates switch  62  to cause current source  60  to supply current to piezoelectric element  104 . Again, current can be derived from a battery power source or inductive power. Piezoelectric element  104  then actuates detent  106  to permit shaft  98  to clear the detent and move under the spring bias of spring  100 . As alternatives, instead of piezoelectric element  104 , a solenoid or other type of actuator, a fusible link, or bio or agent degradable medium can be used to release the detent  106  from shaft  98 . In some embodiments, detent  106  may be formed from a degradable or fusible material. In each case, the mechanism for releasing the detent  106 , and thereby releasing the mucosal tissue, is controllable. 
       FIG. 11  is a cross-sectional side view of medical device  20 C of  FIG. 10  upon release of the detent  106  from shaft  98 . As shown in  FIG. 11 , shaft  98  is retracted into passage  44  and away from vacuum cavity  46 . In this manner, shaft  98  retracts into passage  44  and releases mucosal tissue  64 , thereby releasing medical device  20 C from engagement with mucosal lining  40 . Medical device  20 C then falls away from mucosal lining  40  and passes through the gastrointestinal tract of patient  12 . 
       FIG. 12  is a flow diagram illustrating a method for attaching and detaching an intra-luminal medical device  20  in accordance with an embodiment of the invention.  FIG. 12  depicts placement of a monitor device within the gastrointestinal tract for purposes of example, although the method can be used in a similar manner for other types of devices, such as electrical stimulators, as well as in other body lumens. As shown in  FIG. 12 , the method involves positioning a monitor within the gastrointestinal tract using an endoscopic delivery device ( 108 ), activating vacuum pressure to draw luminal tissue, e.g., mucosal tissue, into a vacuum cavity ( 110 ), and releasing a spring-loaded shaft to secure the tissue within the cavity ( 112 ). As described herein, the shaft may be a plunger-like shaft that pinches the tissue or a pin-like shaft that penetrates the tissue, either partially or completely. 
     As further shown in  FIG. 12 , upon deactivation of the vacuum pressure ( 114 ), the method involves withdrawing the endoscopic delivery device ( 116 ) from the gastrointestinal tract and activating the monitor to sense one or more physiological conditions within the gastrointestinal tract ( 118 ). After a desired monitoring time or upon completion of a desired course of treatment, in the case of a therapy device such as a stimulator, a detachment mechanism is activated to detach the device from the tissue ( 120 ), permitting the device to pass through the gastrointestinal tract. As described herein, detachment may be accomplished in a variety of ways, such as by energization of a solenoid coil, energization of a piezoelectric element, or destruction of a fuse link in the shaft. 
       FIG. 13  is another flow diagram illustrating a method for attaching and detaching an intra-luminal medical device in accordance with another embodiment of the invention. Again, placement of a monitor device within the gastrointestinal tract will be described for purposes of illustration. In the example of  FIG. 13 , the method involves positioning a monitor within the gastrointestinal tract using an endoscopic delivery device ( 122 ), activating vacuum pressure to draw luminal tissue, e.g., mucosal tissue, into a vacuum cavity ( 124 ), and releasing a spring-loaded shaft to secure the tissue within the cavity ( 126 ). Upon deactivation of the vacuum pressure ( 128 ) and withdrawal of the endoscopic delivery device ( 130 ), the monitor is activated to sense gastrointestinal tract conditions ( 132 ), and continues to monitor the conditions until a timer maintained by a clock carried by the sensor exceeds a maximum time ( 134 ). At this point, the detachment mechanism is activated in order to detach the monitor from the mucosal tissue within the gastrointestinal tract ( 136 ). 
       FIG. 14  is a cross-sectional side view of an endoscopic delivery device  135  for forming a bonding agent to attach an intra-luminal medical device  20  in accordance with an embodiment of the invention. Endoscopic delivery device  135  includes a distal end portion  137  attached to an elongated probe member  70 . Medical device  20  is mounted within a placement bay  141 . In the embodiment of  FIG. 14 , the fixation mechanism is a bonding agent that forms a bond between medical device  20  and mucosal lining  40 . The bond attaches medical device  20  to a target tissue location within the body lumen. The detachment mechanism is a degradation agent that rapidly degrades the bonding agent to release medical device  20  from mucosal lining. 
     The bonding agent may be a surgical adhesive such as any of a variety of cyanoacrylates, derivatives of cyanoacrylates, or any other adhesive compound with acceptable toxicity to human gastrointestinal cells that provides the necessary adhesion properties required to secure medical device  20  to the target location. Adhesives may be injected or otherwise applied into the region surrounding the target location, e.g., via a one or more channel within the endoscopic delivery device  135 , or carried by the medical device  20  itself. 
     In the example of  FIG. 14 , endoscopic delivery device  135  includes two delivery channels  138 ,  140  for delivery of constituent components  146 ,  148  of a bonding agent through ports  142 ,  144 , respectively. Delivery channels  138 ,  140  extend along the length of elongated probe member  139  to respective sources of the constituent components at a proximal end of endoscopic delivery device  135 . Constituent components  146 ,  148  may form parts of a two-part, cyanoacrylate-based epoxy compound. For example, one of components  146 ,  148  may be an epoxy resin and the other may be a hardener. 
     Upon introduction of components  146 ,  148  via ports  142 ,  144  of endoscopic delivery device  135 , the components flow over mucosal lining  40  and mix to form a bonding agent, e.g., within a few seconds. In some embodiments, UV- or thermally-curable bonding agents may be used, in which cases endoscopic delivery device  135  may further include a UV source or heating element to cure the bonding agent. Following mixing of components  146 ,  148 , a physician may advance endoscopic delivery device  135  so that medical device  20  is placed in contact with the resulting mixture. An endoscopic viewing device may be provided to aid in placement of medical device  20  relative to the mixture. Although  FIG. 14  depicts injection of components  146 ,  148  via endoscopic delivery device  135 , in some embodiments, medical device  20  may carry a supply of the bonding agent or constituent components, e.g., on a surface of the medical device. 
       FIG. 15  is a cross-sectional side view of the endoscopic delivery device  135  following attachment of medical device  20  with a bonding agent  150  formed by components  146 ,  148 . The physician releases medical device  20  either actively with a push rod or other device, or passively by pulling endoscopic delivery device  135  away from the medical device, which bonds to the bonding agent.  FIG. 16  is a side view of the medical device  20  of  FIGS. 14 and 15  following withdrawal of the endoscopic delivery device  135 . As shown in  FIG. 16 , the capsule-like housing of medical device  20  remains attached to mucosal lining via bonding agent  150 .  FIG. 17  is a cross-sectional end view of a body lumen in which medical device  20  of  FIGS. 14-16  is implanted. 
     In the example of  FIGS. 14-17 , the fixation mechanism is provided by a bonding agent. In this case, the detachment mechanism in accordance with the invention is an agent for rapidly degrading the bonding agent in order to selectively release medical device  20  from mucosal lining  40  in a controlled manner. As an example, patient  20  may ingest a selected degradation agent that travels through the body lumen in which medical device  20  is implanted. Alternatively, a degradation agent may be introduced by injection or by an endoscopic device. Examples of rapid degradation agents for a bonding agent of the type described above may include biocompatible depolymerization agents to rapidly degrade polymeric bonding agents. Examples of deployermization agents include mild acids, bases or peroxides. Another example of a rapid degradation agent is the introduction of thermal energy to melt the bonding agent. The thermal energy can be generated by the medical device  20  itself, by application of a thermal element carried by an endoscopic delivery device, by localized heating of the endoscopic delivery device with an endoscopic device, or by directed external heating such as ultrasonically generated heat. Localized heating of the medical device  20  could be accomplished by applying radio frequency (RF) current across the medical device or the bonding agent using electrodes carried by an endoscopic device. 
     Other examples of suitable bonding agents for use as a fixation mechanism as shown in  FIGS. 14-17  include biologically mediated bonding agents such as fibrin glues. A fibrin glue, such as Tissucol, includes concentrated fibrinogen and factor XII combined with thrombin and calcium to form a coagulum. Fibrin glue may be introduced by an endoscopic delivery device  135  as shown in  FIGS. 14-17  at a target tissue location. To activate the fibrin glue, endoscopic delivery device  135  may further introduce calcium so that the final stage of the clotting cascade is stimulated, producing a fibrin clot within seconds. The resulting clot securely attaches medical device  20  to mucosal lining  40 . 
     In this embodiment, the detachment mechanism is a rapid degradation agent that breaks down the fibrin clot. For example, the patient may ingest a targeted degradation agent such as streptokinase to dissolve the clot and thereby release medical device from mucosal lining  40 . Alternatively, the degradation agent may be injected or introduced by an endoscopic delivery device. A physician may supervise ingestion of the degradation agent, or the patient may simply ingest the degradation agent at a prescribed time or date. 
     Hence, a biologically mediated bonding agent permits secure attachment of medical device  20 , as well as selective detachment on a controlled basis. Other biologically mediated bonding agents that may be suitable for this purpose include glues based on collagen, albumin or gelatin. 
       FIG. 18  is a flow diagram illustrating attachment and detachment of an intra-luminal medical device with a bonding agent and a degradation agent in accordance with an embodiment of the invention. Again, a monitor device and the gastrointestinal tract will be described for purposes of illustration. As shown in  FIG. 18 , a physician positions a monitor within the gastrointestinal tract using an endoscopic delivery device ( 152 ), applies a biological bonding agent to the tissue wall ( 154 ), and places the monitor in contact with the bonding agent ( 156 ). The physician applies an activating agent either before placement of the monitor or after placement ( 158 ). For example, constituent components of a cyanoacrylate compound may be introduced and mixed just prior to placement of the monitor, or simultaneously with placement. Alternatively, for a biologically mediated bonding agent, a patient may ingest an activating substance such as calcium upon placement of the monitor. Upon withdrawal of the endoscopic delivery device ( 160 ), the monitor is activated to sense physiological conditions within the gastrointestinal tract ( 162 ). When desired, the monitor is released from the tissue by applying a deactivating agent such as a rapid degradation agent that breaks down the bonding agent ( 164 ). 
     The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein may be employed without departing from the invention or the scope of the claims. For example, the invention is not limited to deployment of a medical device at a particular location within the gastrointestinal tract. In various embodiments, a medical device may be located anywhere within the gastrointestinal tract. For example, the medical device may be affixed along or to any of the other structures and organ walls along the gastrointestinal tract, including the colon, small intestine, stomach, or the esophagus. Alternatively, the medical device may be implanted within other body lumens within a patient, such as blood vessels or the urethra. 
     The invention also is not limited to monitoring or electrical stimulation, but also may encompass medical devices configured to deliver different types of therapies or to serve different diagnostic purposes. In addition, the invention is not limited to application for monitoring or therapy applications associated with any particular disorder, condition or affliction. 
     In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts a nail and a screw are equivalent structures. 
     Many embodiments of the invention have been described. Various modifications may be made without departing from the scope of the claims. These and other embodiments are within the scope of the following claims.