Patent Publication Number: US-2006020225-A1

Title: Wireless urodynamic monitoring system with automated voiding diary

Description:
This application claims the benefit of U.S. provisional application No. 60/589,442, filed Jul. 20, 2004, and U.S. provisional application No. 60/589,542, filed Jul. 20, 2004, the entire content of each of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The invention relates to medical devices and, more particularly, devices for monitoring urodynamic conditions.  
     BACKGROUND  
      Many people suffer from involuntary urine leakage, i.e., urinary incontinence. Others may suffer from blocked or restricted urine flow. Other urinary disorders include frequent urination, sudden urges to urinate, problems starting a urine stream, painful urination, problems emptying the bladder completely, and recurrent urinary tract infections. A physician uses a urodynamic test to study how a patient stores and releases urine. During the test, the physician obtains urodynamic information based on one or more physiological conditions within the urinary tract.  
      Different muscles, nerves, organs and conduits within the urinary tract cooperate to collect, store and release urine. A variety of disorders may compromise the urinary tract performance and contribute to incontinence or restricted flow. Many of the disorders may be associated with aging, injury or illness. For example, aging can often result in weakened sphincter muscles, which cause incontinence, or weakened bladder muscles, which prevent complete emptying. Some patients also may suffer from nerve disorders that prevent proper triggering and operation of the bladder or sphincter muscles.  
      Urodynamic sensing can reveal how well the bladder and sphincter muscles perform, and may help identify the causes of various urinary tract disorders. Urodynamic sensing can take the form of simple observation or precise measurement using monitors that sense physiological conditions such as urine pressure, flow, velocity, volume, and the like. Some monitors sense the occurrence and force of bladder contractions to identify abnormal bladder function. Other monitors may determine a volume of urine remaining in the bladder following urination. Hence, urodynamic sensing may focus on the ability of the bladder to empty steadily and completely.  
      Urodynamic testing ordinarily requires catheterization of the patient in order to place a monitor within the bladder or urethra. For this reason, urodynamic testing typically takes place within a clinical setting. In some cases, the presence of a catheter can disrupt the normal physiological function of the urinary tract. Although ambulatory catheterization is possible, it can be uncomfortable and may result in measurements that are not be representative of normal physiological function. In addition, the urinary catheter can be uncomfortable for the patient.  
      Various urodynamic testing systems are described in U.S. Pat. No. 4,873,990 to Holmes et al., U.S. Pat. No. 5,331,548 to Rollema et al., and U.S. Pat. No. 6,454,720 to Clerc et al. Siwapomsathain et al. describe a bladder monitor with wireless telemetry in Siwapornsathain et al., “A Telemetry and Sensor Platform for Ambulatory Urodynamics,” Proceedings of the 2nd Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine &amp; Biology, Madison, Wis., 2002. J. Coosemans et al. describe an implantable bladder pressure monitor with wireless telemetry in “Datalogger for Bladder Pressure Monitoring With Wireless Power and Data Transmission,” Katholieke Universiteit Leuven, Department ESAT-MICAS, Belgium, Belgian Day on Biomedical Engineering, 2003.  
      Table 1 below lists documents that disclose various techniques for urodynamic testing.  
                       TABLE 1                           Inventors/           Patent Number   Author   Title                  4,873,990   Holmes et al.   Circumferential Pressure Probe       5,331,548   Rollema et al.   Method and system for on-line measure-               ment, storage, retrieval and analysis               of urodynamical data       6,454,720   Clerc et al.   System for measuring physical para-               meters with a medical probe       Not applicable   J. Coosemans   Datalogger for Bladder Pressure Moni-           et al.   toring With Wireless Power and Data               Transmission       Not Applicable   Siwapornsa-   A Telemetry and Sensor Platform for           thain et al.   Ambulatory Urodynamics                  
 
      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 a wireless urodynamic monitoring system with an automated voiding diary feature. The system senses and records urodynamic information in response to a user command or in response to detection of the onset of a voiding event. The urodynamic information obtained over a series of voiding events forms an automated voiding diary that is useful in diagnosis of urological disorders. An implantable monitor obtains the urodynamic information and either records the information locally or transmits the information to an external controller via a wireless telemetry link. In some embodiments, the external controller may include a loop recorder for recording urodynamic information obtained by the implantable monitor over an extended period of time.  
      Various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to prior art systems for urodynamic monitoring. These problems include the general inconvenience and discomfort experienced by the patient during the use of catheter-based urodynamic monitoring systems. Other problems relate to potential inconsistencies involved in the manual preparation of voiding diaries by individual patients. Further problems relate to the difficulty in the transfer and analysis of voiding diary information. Such problems can limit the collection and analysis of useful urodynamic information, and undermine the integrity and diagnostic efficacy of the information.  
      Various embodiments of the present invention are capable of solving at least one of the foregoing problems. When embodied in a system or method for wireless urodynamic monitoring, the invention includes features that facilitate automated formulation of a voiding diary. A wireless urodynamic monitoring system, in accordance with the invention, includes a wireless implantable monitor and an external controller. The implantable monitor and external controller can accompany the patient throughout a routine of normal daily activities.  
      The implantable monitor is configured for indwelling urodynamic monitoring within the bladder or urethra. The wireless implantable monitor obtains urodynamic information in response to a voiding event activation command entered into the external controller or automated detection of the onset of a voiding event. The monitor may be configured to transmit the information to the external controller. In this manner, the monitoring system selectively records urodynamic information obtained at the time of a voiding event.  
      In comparison to known techniques for monitoring urodynamic parameters, various embodiments of the invention may provide one or more advantages. For example, the invention facilitates the automated acquisition, transfer and analysis of voiding diary information. In addition, the use of a wireless urodynamic monitor can reduce patient inconvenience and discomfort, and facilitate urodynamic monitoring as the patient goes about his daily routine. Also, by acquiring urodynamic information automatically in response to either patient input or detection of the onset of a voiding event, a wireless monitoring system supports convenient recording of urodynamic information that is particularly relevant and useful in diagnosis of urological disorders. Automated formulation of a voiding diary also avoids potential inconsistencies in manual voiding diaries, which may rely on individual patient discipline.  
      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 a wireless urodynamic monitor and an external controller shown in conjunction with the bladder and urethra of a patient.  
       FIG. 2  is a functional block diagram illustrating a wireless urodynamic monitor with a telemetry interface for communication with an external controller.  
       FIG. 3  is a functional block diagram illustrating an external controller with a telemetry interface for wireless communication with an implanted urodynamic monitor.  
       FIG. 4  is flow diagram illustrating operation of a urodynamic monitor and external controller in response to a voiding activation input from a patient.  
       FIG. 5  is flow diagram illustrating operation of a urodynamic monitor and external controller in response to a sensed voiding event.  
       FIG. 6  is a functional block diagram illustrating a network for communication of information obtained by wireless urodynamic monitors.  
       FIG. 7  is a cross-sectional side view of a wireless urodynamic monitor attached to a tissue site within the bladder or urethra.  
       FIG. 8  is a schematic diagram illustrating deployment of the monitor of  FIG. 7  within a patient&#39;s urinary tract with an endoscopic delivery device.  
       FIG. 9  is a cross-sectional side view of the wireless urodynamic monitor and distal end of the endoscopic delivery device of  FIGS. 7 and 8 .  
       FIG. 10  is a side view of a monitor with a fixation structure in the form of an expandable frame.  
       FIG. 11  is a conceptual diagram of an external controller equipped to record and present information obtained from an implantable urodynamic monitor.  
       FIG. 12  is another conceptual diagram of the external controller of  FIG. 11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  is a schematic diagram illustrating a wireless urodynamic monitoring system  10  including an implanted urodynamic monitor  12  and an external controller  14  shown in conjunction with a patient  16 . System  10  collects and records urodynamic information in response to a voiding event activation command. The voiding event activation command may be entered into external controller  14  by patient  16  to indicate the onset of a voiding event. Alternatively, the voiding event activation command may be generated automatically within monitor  12  or external controller  14  upon detection of urodynamic information indicating the onset of a voiding event. Implantable monitor  12  and external controller  14  cooperate to form an automated voiding diary containing urodynamic information obtained over a series of voiding events.  
      Urodynamic monitor  12  may be implanted within a patient bladder  18  or urethra  20  forming part of the patient&#39;s urinary tract. In  FIG. 1 , urodynamic monitor  12  is shown at a target location within bladder  18 , but alternatively may be implanted within urethra  20 . In some embodiments, multiple urinary tract monitors  18  may be placed within the urinary tract. Monitor  12  may be placed at a target location within the urinary tract by endoscopic delivery, e.g., using a catheter, cystoscope, endoscope, or the like, as will be described in greater detail. Monitor  12  may be implanted temporarily or chronically.  
      The target location may be within bladder  18  or within urethra  20 . As will be described in greater detail, monitor  12  may include any of a variety of fixation structures to securely position the monitor at a target tissue location within the urinary tract. Upon fixation of monitor  12 , the endoscopic delivery device may be withdrawn from the urinary tract of patient  16 . In this manner, monitor  12  can remain in a desired position for an extended period of time, and accompany patient  16  outside the clinic or hospital and throughout a routine of daily activities.  
      Urodynarnic information, as used herein, generally refers to physiological information characterizing or relating to the function of the bladder  18 , urethra  20 , or other segments of a patient&#39;s urinary tract in storing, releasing, and passing urine. The urodynamic information may include urine pressure, flow, velocity, temperature, impedance, or the like, as well as contractile activity of bladder  18 . A voiding event, as used herein, generally refers to a time at which a patient attempts to void urine from the bladder, feels discomfort in the bladder or urethra, or experiences involuntary urine leakage or other urinary incontinence symptoms. Each type of voiding event can provide important urodynamic information for evaluation of urological health. A voiding diary, in general, refers to a set of urodynamic information associated with particular voiding events.  
      Patient  16  may activate urodynamic monitor  12  to collect urodynamic information during or proximate to a urinary voiding event. For example, patient  16  may activate urodynamic monitor  12  by entering a voiding event activation command into external controller  14  to indicate the onset of a voiding event, such as an attempt to void urine from bladder  18 . In response, external controller  14  transmits a wireless command to urodynamic monitor  12 , which then captures one or more measurements of urodynamic parameters within bladder  18  or urethra  20  to form a set of urodynamic information. Alternatively, in some embodiments, urodynamic monitor  12  may automatically detect the onset of a voiding event, and automatically trigger the collection of urodynamic information.  
      In some embodiments, urodynamic monitor  12  transmits the urodynamic information to external controller  14 , e.g., as the information is obtained. External controller  14  generates a voiding diary that contains a record of voiding events and urodynamic information measured by urodynamic monitor  12  during the voiding events. In this manner, external controller  14  selectively records relevant information obtained at the time a patient experiences a voiding event, such as an attempt to void urine from the bladder. Hence, there is no need for the patient  16  to make a manual voiding diary. Also, the automated voiding diary contains objective urodynamic information, rather than subjective impressions from the patient.  
      In other embodiments, rather than immediately transmitting the urodynamic information to external controller  14 , monitor  12  may initially store the information internally for subsequent wireless transmission to external controller  14  or another device. Hence, in some embodiments, the urodynamic information may be stored within monitor  12 , and later transmitted to external controller  14  upon interrogation of the monitor. Interrogation may be initiated by the patient  16  by entering a command into external controller  14 . In further embodiments, monitor  12  may store the information internally on a persistent basis for later retrieval by external controller  14 , or upon explantation of the monitor.  
      Urodynamic monitor  12  is configured for indwelling urodynamic testing within the bladder  18  or urethra  20 . In this manner, monitor  12  can accompany patient  16  throughout a routine of normal daily activities. In some embodiments, multiple urodynamic monitors  12  may be implanted within the urinary tract of patient  16 . External controller  14  may take the form of a handheld, external recorder that is carried by patient  16 .  
      Urodynamic monitor  12  may obtain a variety of urodynamic information relating to physiological conditions within the bladder  18  or urethra  20  during a voiding event. For example, the physiological conditions may include one or more urodynamic conditions such as urine pressure, urine volume, urine flow, urine pH, temperature, bladder contraction, or urinary sphincter contraction. The urodynamic information may represent averages, trends, or instantaneous measurements, as well as information representing specific events during the course of voiding. As a further example, implanted monitor  12  may measure and record an indication of the residual volume of urine following a voiding event. Residual volume is another important parameter in urodynamic studies to measure the effectiveness of the voiding bladder condition. In some embodiments, urodynamic monitor  12  and external controller  14  may be configured as loop recorders to overwrite their respective memories with new information as the memory becomes full.  
       FIG. 2  is a functional block diagram illustrating implantable urodynamic monitor  12  of  FIG. 1 . In the example of  FIG. 2 , monitor  12  includes a processor  24 , a sensor  26 , memory  28 , wireless telemetry interface  30 , and a power source  32 . Monitor  12  also may include an internal clock to track date and time of voiding events. In accordance with the invention, monitor  12  obtains urodynamic information via sensor  26  in response to a voiding event activation command, which may be initiated by a user or generated automatically upon detection of the onset of a voiding event.  
      Monitor  12  may be entirely self-contained, self-powered and integrated within a common housing using miniaturized integrated circuitry available to those skilled in the art. In some embodiments, for example, monitor  12  may be constructed in a manner similar to the monitors described in U.S. patent application Ser. No. 10/833,776, to Mark Christopherson and Warren Starkebaum, filed Apr. 28, 2004, entitled “Implantable Urinary Tract Monitor,” the entire content of which is incorporated herein by reference.  
      Power source  32  may take the form of a small battery. An external source of inductively coupled power may be used, in some embodiments, to power some features of monitor  12 . For example, monitor  12  may include an inductive power interface for transcutaneous inductive power transfer to power higher energy functions such as telemetry. However, monitor  12  typically will include a small battery cell within the monitor housing. Alternatively, monitor  12  may include an inductive power interface in lieu of a battery.  
      Telemetry interface  30  permits wireless communication with external controller  14  for wireless transmission of information obtained by sensor  26 , as well as wireless reception of a voiding event activation command directing monitor  12  to collect physiological information during an attempt to void urine from the bladder. As a further alternative, the voiding event activation command may be applied by patient  16  in the form of a magnet swiped in proximity to monitor  12 , in which case the monitor will include appropriate sensing circuitry to detect the magnet. Accordingly, an optional magnet detector  33  is shown in  FIG. 3 .  
      Processor  24  controls telemetry interface  30  and handles processing and storage of information obtained by sensor  26 . Processor  24  controls operation of monitor  12  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, or a combination thereof. Memory  28  may store program instructions that, when executed by processor  24 , cause the controller to perform the functions ascribed to it herein. For example, memory  28  may store instructions for processor  24  to execute in support of control of wireless telemetry interface  30  and control of, and processing of information obtained by, sensor  26 . Memory  28  may include separate memories for storage of instructions and urodynamic information.  
      Telemetry interface  30  may include a wireless radio frequency (RF) transmitter and receiver to permit bi-directional communication between monitor  12  and external controller  14 . In this manner, external controller  14  may transmit commands to urodynamic monitor  12  for collection of urodynamic information or collection of information stored in memory  28 , and receive status and operational information from the monitor. Telemetry interface  30  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 monitor  12 . Alternatively, the antenna may be mounted on a circuit board carrying other components of monitor  12 , or take the form of a circuit trace on the circuit board.  
      Battery power source  32  may take the form of a battery and power generation circuitry. Urodynamic monitor  12  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  32  may be very small. An example of a suitable battery is the Energizer  337  silver oxide cell, available from the Eveready Battery Company, of St. Louis, Mo., USA. The Energizer  337  battery is disc-shaped, and has a diameter of 4.88 mm and thickness of 1.65 mm. Another example battery is the QL003I3 milliamp cylindrical battery from Quallion, LLC, of Sylmar, Calif., USA, which has a diameter of approximately 2.9 mm and a length of approximately 13.0 mm.  
      In further embodiments, battery power source  32  may be rechargeable via electromagnetic induction or ultrasonic energy transmission, and includes an appropriate circuit for recovering transcutaneously received energy. For example, battery power source  32  may include a secondary coil and a rectifier circuit for inductive energy transfer. In still other embodiments, battery power source  32  may not include any storage element, and monitor  12  may be fully powered via transcutaneous inductive energy transfer, which may be provided by external receiver  14 .  
      Sensor  26  may be selected for any of a variety of urodynamic testing applications, and may include appropriate signal processing circuitry such as amplifier, filter, driver, and analog-to-digital conversion circuitry for presentation of sensed information to processor  24 . For urodynamic testing, sensor  26  may take the form of a pressure, flow, velocity, volume, temperature, impedance, or contractile force sensor.  
      Pressure, contractile force or other measurements may be used to detect bladder or urinary sphincter functions in order to automatically detect the onset of an attempt to void urine from bladder  18 . For example, an elevated pressure or force, or change in pressure or force, may indicate a contraction of the bladder muscle, which may be used to generate a voiding event activation command to trigger collection of urodynamic information for recording in a voiding diary. As a further example, if monitor  12  is implanted within urethra  20 , the voiding event may be detected by detecting the presence of urine in the urethra, e.g., by flow, pressure, temperature, or impedance sensing. Accordingly, in some embodiments, the use of two monitors  12  may be desirable, e.g., one in bladder  18  and one in urethra  20 . Hence, for automated detection, processor  24  may periodically sample and monitor the output of sensor  26 . In some embodiments, monitor  12  may transmit the periodically sampled information to external controller  14 , which then analyzes the information to detect a voiding event.  
      For urodynamic testing, sensor  26  may have a structure similar to sensors conventionally used for catheter-based urodynamic testing. For pressure measurements, for example, sensor  26  may include one or more diaphragm sensors, strain gauge sensors, capacitive sensors, piezoelectric sensors, or other sensors used in conventional catheter-based urodynamic testing to sense pressure. For bladder emptying, sensor  26  may include a conductive sensor to sense the presence of urine within the lower region of the bladder  18 .  
      For flow measurements, sensor  26  may comprise a pulsed Doppler ultrasonic sensor, or a laser Doppler flow sensor. Doppler shifting of the frequency of the reflected energy indicates the velocity of the fluid flow passing over a surface of sensor  26 . Consequently, in some embodiments, monitor  12  may include circuitry, such as a quadrature phase detector, in order to enable the monitor to distinguish the direction of the flow of fluid in addition to its velocity.  
      As a further example, sensor  26  may include any one or more thermal-convection velocity sensors. A thermal-convection velocity sensor may include a heating element upstream of a thermistor to heat urine within the urethra  16  such that flow rate may be measured according to the temperature of the heated fluid when it arrives at the thermistor. In other embodiments, flow rate may be determined from the output of a concentration or temperature sensor using Fick&#39;s techniques.  
      In some embodiments, sensor  26  may include multiple sensors of a given type, as well as multiple types of sensors, e.g., pressure, flow, bladder emptying, or the like. Accordingly, the urodynamic information obtained by monitor  12  may then include different types of physiological parameters associated with a voiding event. Alternatively, multiple monitors  12  may be deployed within bladder  18  or urethra. In this case, each monitor  12  may be configured with a different type or set of sensors  26  to collect a variety of different urodynamic parameters during a voiding event.  
      In response to a voiding event activation command, monitor  12  obtains urodynamic information from sensor  26  and either records the information in internal memory  28  carried by the monitor, or transmits the information directly to external controller  14  by wireless telemetry. In some embodiments, monitor  12  also may be capable of continuously or periodically performing urodynamic testing over an extended period of time, encompassing voiding events and measurements between voiding events.  
      By selectively obtaining urodynamic information associated with voiding events, however, monitor  12  is configured to support the generation of an automatic urinary voiding diary containing urodynamic information obtained over a series of voiding attempts. Again, in response to the voiding event activation command, monitor  12  commences sensing of one or more physiological conditions within bladder  18  or urethra  20 , and either records pertinent information internally, transmits the information directly to external controller  14 , or temporarily buffers and then transmits the information to external controller  14 , either directly or in response to an interrogation request by the external controller.  
      In embodiments in which information is stored internally within monitor  12 , the monitor may include functionality similar to the existing Medtronic Reveal™ implantable loop recorder, manufactured by Medtronic, Inc. of Minneapolis, Minn. The Reveal™ implantable loop recorder samples and records one or more segments of far field EGM or subcutaneous ECG signals.  
      Aspects of the Reveal™ loop recorder are disclosed in commonly assigned PCT publication WO98/02209, the entire content of which is incorporated herein by reference. In accordance with the invention, monitor  12  may be adapted to sample and record one or more segments of information pertaining to physiological conditions within the urinary tract. In some embodiments, the memory capacity of memory  28  in monitor  12  may be limited, and so the segments of information that are stored in memory can be written over with new information when the patient triggers storage and the memory is full.  
      The most recently stored segment or segments of information may be transmitted via uplink telemetry transmission from monitor  12  to external controller  14  on a continuous or periodic basis, or when a memory interrogation telemetry session is initiated by a medical care provider using the external controller. In other embodiments, external controller  14  may be configured to avoid overwriting, and instead retain previously sensed information when the memory with the external controller is full.  
       FIG. 3  is a functional block diagram illustrating external controller  14  for communication with urodynamic monitor  18  of  FIG. 2 . In the example of  FIG. 3 , external controller  14  includes a processor  34 , memory  36 , power source  38 , telemetry interface  40 , user input  42  and display  44 . Memory  36  stores instructions for execution by processor  34 . In addition, memory  36  stores information received from monitor  12  incident to a voiding event, thereby forming an automated voiding diary for review by a physician. Memory  36  may include separate memories for storage of instructions and urodynamic information.  
      Processor  34  controls telemetry interface  40  to obtain urodynamic information from monitor  18 . Processor  34  also may control telemetry interface  40  to receive information from monitor  18  on a substantially continuous basis, at periodic intervals, or only upon receipt of a user activation command. Hence, external controller  14  may obtain on ongoing, up-to-date indication of the physiological conditions sensed by monitor  12 . More particularly, however, external controller  14  is configured to respond to a voiding event activation command  46  entered by patient  16  via user input device  42 . In response to the voiding event activation command  46 , external controller  14  generates an activation control signal and transmits the control signal to monitor  12  via telemetry interface  40 .  
      Urodynamic monitor  12  may be configured to collect information for a specified period of time following receipt of an activation control signal from external controller  14 , e.g., for a period of several minutes. Alternatively, external controller  14  may receive a voiding event deactivation command (not shown) from the user. In this case, external controller  14  transmits a deactivation control signal to urodynamic monitor  12 . Accordingly, monitor  12  may be configured to collect urodynamic information from the time an activation control signal is received to the time a deactivation control signal is received.  
      External controller  14  permits a user to receive urodynamic information obtained by a sensor carried by monitor  12  during the course of a voiding event. In addition, external controller  14  may process and record information obtained from monitor  12 , and present the information to a user via display  44  or other output media. In some embodiments, the information may include one or more advisories with respect to the presence or level of a urodynamic parameter. In addition, the recorded information may be transmitted from external device  14  to other external devices for presentation, archival or further analysis.  
      Advantageously, the recorder functionality of the external controller  14  serves to build a voiding diary. In particular, by permitting a patient  16  to activate sensing and recording coincident with a voiding event, external controller  14  is able to compile information specifically associated with one or more voiding events over an observation period. Consequently, a physician can view a more selective set of urodynamic information, which may be very useful in diagnosing symptoms such as incontinence, pain, or the like. In particular, a physician can parse through multiple entries in the voiding diary to identify changes in physiological conditions over time, or at different times of the day or night.  
      Wireless telemetry may be accomplished by radio frequency (RF) communication or proximal inductive interaction of external controller  14  with monitor  12 . Alternatively, telemetry interfaces  30 ,  40  may be configured for monitor  12  and external controller  14  to support radio frequency (RF) communication with a sufficiently strong signal such that proximate interaction is not required. In addition to an RF or inductive telemetry interface  40 , in some embodiments, external controller  14  may include an additional RF or infrared interface for communication with other external devices, e.g., for transfer of urodynamic information.  
      External controller  14  may take the form of a portable, handheld device, like a pager or cell phone, that can be carried by patient  12 . External controller  14  may include an internal antenna, an external antenna protruding from the recorder, or an external antenna that extends from the recorder on a cable and is attached to the body of patient  12  at a location proximate to the location of monitor  12  to improve wireless communication reliability. Also, in some embodiments, external controller  14  also may receive operational or status information from monitor  12 , and may be configured to actively configure and interrogate the monitor to receive the information.  
       FIG. 4  is flow diagram illustrating operation of a urodynamic monitor  12  and external controller  14  in response to a voiding event activation command from a patient. As shown in  FIG. 4 , external controller  14  receives a voiding event activation command from patient  16  ( 48 ). In response, external controller  14  transmits a control signal to monitor  12  instructing the monitor to initiate sensing of one or more physiological parameters of the urinary tract ( 50 ). Implanted monitor  12  transmits urodynamic information, based on the sensed physiological parameters. External controller  14  receives the urodynamic information from implanted monitor  12  ( 52 ). External controller  14  then processes the information received from monitor  12 , if necessary, and records the information in memory for evaluation by a physician or other care-giver ( 54 ).  
      Urodynamic monitor  12  may continue to collect urodynamic information for a specified period of time following receipt of the activation command. Upon expiration of the specified period of time, monitor  12  automatically terminates collection of urodynamic information. The specified time may be selected to correspond to the maximum expected duration of a voiding event, such as an attempt to void urine from the bladder, and may be on the order of several seconds to a few minutes.  
      Alternatively, as shown in  FIG. 4 , implanted monitor  12  may terminate collection of urodynamic information in response to a termination command received from external controller  14 . For example, a patient may enter a voiding deactivation command into external controller  14  ( 56 ), e.g., at the end of a voiding event. In response, external controller  14  transmits a control signal to instruct monitor  12  to terminate sensing of urodynamic parameters ( 58 ).  
      During a voiding event, monitor  12  may intermittently or continuously transmit urodynamic information to external controller  14 , e.g., in the form of measured parameters obtained at different sample times during the course of monitoring. Alternatively, monitor  12  may transmit information at the end of a monitoring period, either as measured parameters or processed values, such as average or trend data. Once the information is transmitted, monitor  12  waits for the next activation command for a subsequent voiding event.  
       FIG. 5  is flow diagram illustrating operation of a urodynamic monitor  12  and external controller  14  in response to a sensed voiding event. In the example of  FIG. 5 , monitor  12  does not require a voiding event activation command from the patient  16 . Instead, monitor is configured to automatically sense a voiding event ( 49 ), e.g., by detection of an elevation or change in pressure or urine flow. Upon automated detection of a voiding event, urodynamic monitor  12  initiates sensing of physiological parameters ( 51 ), and records urodynamic information based on the sensed parameters ( 53 ). The urodynamic information may be recorded within memory in monitor  12 , and later transmitted to external controller  14  upon receipt of an interrogation request ( 55 ). Alternatively, the urodynamic information may be transmitted to external controller  14  as the information is obtained by monitor  12 .  
       FIG. 6  is a functional block diagram illustrating a network  60  for communication of information obtained by one or more urodynanic monitors  12 . Two implanted urodynamic monitors  12 A,  12 B, e.g., in different patients, are shown for purposes of illustration. However, information for any number of monitors  12  and patients  16  may be accessed via network  60 . In particular, physicians or other medical personnel may view urodynamic information transmitted to external controllers  14 A,  14 B by implanted monitors  12 A,  12 B to evaluate urodynamic conditions. External controllers  14 A,  14 B are coupled to network  60  via wired or wireless connections, and transmit information obtained from monitors  12 A,  12 B to a network server  62  via the network.  
      Network server  62  may be equipped to analyze the information and generate appropriate reports or advisories for viewing by users via any of network clients  64 A,  64 B,  64 C (collectively  64 ), coupled to network  60 . For example, network server  62  may generate web pages or other output that conveys voiding diary information obtained by monitors  12 A,  12 B. Hence, network clients  64  may access information on network server  62  using web browsers. In this manner, one or more users, such as physicians, may remotely view voiding diaries for one or more patients  16 . Network  60  may take the form of a local area, wide area or global computer network, such as the Internet.  
      In some embodiments, network server  62  may be configured to poll external controllers  14  to received information. Network server  62  also may be configured to transmit advisories by email, facsimile, text messaging, instant messaging or the like to network clients  64 , when voiding diary results are available for a particular patient. In this manner, the user associated with a network client  64  is able to remotely monitor information concerning a patient&#39;s condition, as obtained by the implanted monitor  12 , and act on that information, if appropriate.  
      The ability to formulate an automated voiding diary with a temporary or chronic implanted monitor  12 , combined with remote monitoring capabilities, can support a wide range of patient management capabilities, tight control of drug management, disease diagnostics, and chronic disease management. In addition, the ability to formulate a voiding diary while that patient is at home and going about daily living activities can provide much more accurate and meaningful data. For example, a pressure monitor in the bladder may be used to monitor bladder function during voiding events occurring over a period of several days, and over the course of several activities such as rest, eating, drinking, and exercise.  
      Implanted monitor  12  also may be used chronically for management of spinal cord injury patients who do not have bladder sensation. Rather than timed, intermittent catheterization, implanted monitor  12  would allow a spinal cord injury patient to monitor fullness and void only when necessary. In this case, monitor  12  could transmit a signal to external controller  14  when a particular level of bladder fullness is reached, thereby triggering an alarm or advisory for voiding.  
       FIG. 7  is a cross-sectional side view of a urodynamic monitor  12  with a fixation structure. In the example of  FIG. 7 , monitor  12  is placed adjacent mucosal lining  66  within bladder  18  or urethra  20 . Monitor  12  includes a capsule-like housing  68 . A sensor  26  is exposed by housing  68  for interaction with the environment within bladder  18  or urethra  20 . A shaft  70  extends through an internal channel  72  in the capsule-like housing  68  of monitor  12 . Monitor  12  defines a vacuum cavity  74  on a side of the housing  68  adjacent mucosal lining  66 . A vacuum port defined by channel  72  applies vacuum pressure to vacuum cavity  74  to draw a portion of mucosal tissue  76  into the cavity. The vacuum port is attached to a vacuum line (not shown) carried by an endoscopic delivery device. The vacuum line is coupled to an external vacuum source.  
      An elongated control rod (not shown in  FIG. 7 ) may be applied via the endoscopic delivery device to drive shaft  70  into mucosal tissue  76 . Shaft  70  may have a sharpened tip  77  that facilitates partial or complete penetration of tissue  76 . Upon penetration of tissue  76  to secure monitor  12  relative to mucosal lining  66 , vacuum pressure is deactivated and the endoscopic delivery device is withdrawn from urethra  20 . Although shaft  70  is illustrated as penetrating tissue  76 , in some embodiments, the shaft may be spring-biased to pinch a fold of the tissue and thereby secure monitor  12  at a desired position.  
      In some embodiments, shaft  70  may be manufactured from degradable materials that degrade over time, e.g., in the presence of urine, to release monitor  12  from mucosal lining  66 . Alternatively, monitor  12  may release from mucosal lining  66  as mucosal tissue  76  sloughs away from mucosal lining  66 . In either case, once the mucosal tissue  76  is released by shaft  70 , monitor  12  detaches from mucosal lining  66  for passage through the urinary tract with urine flow or recovery with an endoscopic recovery device. Shaft  70 , vacuum cavity  74  and the vacuum port defined by channel  72  form a fixation structure.  
      In general, monitor  12  may make use of fixation structures that are configured and function in a manner similar to any of the fixation structures disclosed in U.S. Pat. Nos. 6,285,897 and 6,698,056 to Kilcoyne et al. The Kilcoyne et al. patents provide examples of fixation mechanisms for attaching monitoring devices to the lining of the esophagus, including suitable degradable materials. The fixation structures described in the Kilcoyne et al. patents may be suitable for attachment of monitor  12  within bladder  18  or urethra  20 . Examples include shafts, hooks, barbs, screws, sutures, clips, pincers, staples, tacks, and expandable frames. The contents of the Kilcoyne et al. patents are incorporated herein by reference in their entireties.  
      Although sensor  26  is depicted as having one or more surface components exposed to an environment within bladder  18  or urethra  20 , in some embodiments, monitor  12  may include a hollow lumen to allow urine flow through the monitor. In this case, monitor  12  may have an annular cross-section, in a plane perpendicular to urine flow, and sensor  26  may be oriented such that sensor components are exposed to the interior of the hollow lumen. This type of configuration for monitor  12  may be particularly useful within urethra  16 , and can be used to monitor flow rate, pressure, and timing of voiding, which may be advantageous in diagnosing benign prostate hyperplasia (BPH).  
       FIG. 8  is a schematic diagram illustrating deployment of a monitor  12  within a patient&#39;s urinary tract. As shown in  FIG. 8 , an endoscopic delivery device  80  serves to position and place monitor  12  within the urinary tract of patient  16 . Delivery device  80  includes a proximal portion, referred to herein as a handle  82 , and a flexible probe  84  that extends from handle  82  for insertion into urethra  20 . Probe  84  is sized for passage through urethra  20  and may include a lubricating coating to facilitate passage.  
      Monitor  12  is coupled to a distal end  85  of delivery device  80  for delivery to a target location within the urinary tract. The target location may be within urethra  20  or within bladder  18 . In some embodiments, delivery device  80  may include appropriate guidewires or other steering mechanisms to permit placement of monitor  12  on a lateral wall of bladder  18 , as indicated by the position of monitor  12  depicted in  FIG. 1 .  
      Distal end  85  of delivery device  80  enters urethra  20  and extends into the urethra to the target location. The progress of distal end  85  may be monitored by endoscopic viewing or external viewing, e.g., with ultrasound or fluoroscopy. Monitor  12  is attached to the mucosal lining at the target location within bladder  18  or urethra  20 , and the distal end  85  of delivery device  80  releases the monitor. Upon placement of monitor  12 , flexible probe  84  and distal end  85  are withdrawn from urethra  20 . Monitor  12  may be activated prior to placement within the urinary tract, or activated remotely by wireless communication or passage of a magnet in close proximity to monitor  12  to activate a switch carried by the monitor.  
       FIG. 9  is a cross-sectional side view illustrating positioning of monitor  12  of  FIGS. 7 and 8  within distal end  85  of an endoscopic delivery device  80 . As shown in  FIG. 8 , monitor  12  is held within a placement bay within distal end  85  of endoscopic delivery device  80 . In this example, a physician advances elongated control rod  86  to drive shaft  70  into mucosal tissue  76 . In general, elongated control rod  86  permits a physician to exert force to penetrate mucosal tissue  76 . Elongated control rod  86  is flexible and extends though flexible probe  84  to handle  82  so that the physician can manipulate the elongated control rod. Before advancing elongated control rod  86 , however, the physician activates a vacuum line to supply vacuum pressure to vacuum cavity  74  via channel  72  of monitor  12 .  
       FIG. 10  is a side view of a monitor  12  with another fixation structure in the form of an expandable frame  88 . As shown in  FIG. 10 , the capsule-like housing of monitor  12  has a diameter that is substantially less than the diameter of expandable frame  88  when the frame is in a fully expanded state. Upon expansion, frame  88  engages the mucosal lining of the interior wall  66  of urethra  20 , much like a conventional stent used for restoring patency of blood vessels. In this manner, expandable frame  88  securely holds monitor  12  in place at a target location within the urethra  20 . Details of a similar expandable frame and monitor arrangement are described in the aforementioned Christopherson et al. application.  
      The capsule-like housing of monitor  12  is attached to a portion of a wire grid  90  forming expandable frame  88 . Monitor  12  may be welded, adhesively bonded, or crimped to one or more coupling points  92  on expandable frame  88 . Wire grid  90  may take the form of a grid, network, or mesh of elastic wires that form a substantially cylindrical frame, similar to a conventional stent useful in restoring blood vessel patency. Examples of suitable materials for fabrication of wire grid  90  include stainless steel, titanium, nitinol, and polymeric filament, which can be absorbable or nonabsorbable in vivo, as described in the above-referenced Kilcoyne patents.  
      Expandable frame  88  may be intrinsically elastic such that it is self-expandable upon release from a restraint provided by an endoscopic delivery device. Alternatively, in some embodiments, a balloon or other actuation mechanism may be used to actively expand frame  88  to a desired diameter. In each case, expandable frame  88  extends radially outward to engage the wall of a urethra  20 , and thereby place monitor  12  in contact with the lumen wall. In particular, upon expansion of frame  88 , monitor  12  is placed within the lumen defined by urethra  20 , and within the flow of urine through the urethra.  
      The position of monitor  12  within urethra  20  permits sensing of urodynamic parameters, such as pressure, flow rate, velocity, temperature, impedance, contractile force, and the like. In further embodiments, monitor  12  may include an ultrasonic imaging transducer to obtain snapshot ultrasound images of a region of interest during a voiding event. Monitor  12  senses the applicable physiological conditions and transmits information based on the sensed conditions to external controller  14 . In some embodiments, expandable frame  88  may be electrically coupled to monitor  12  and form part of an antenna to facilitate reliable wireless telemetry.  
      Monitor  12  is depicted in  FIG. 10  as being coupled to one side of expandable frame  88 , and therefore resides adjacent a wall of urethra  20 . In other embodiments, however, monitor  12  may be mounted to frame  88  such that monitor resides substantially centrally within urethra  16 . For example, monitor  12  may be cantilevered or otherwise supported by frame  88  with expandable struts that place the monitor centrally within the aperture defined by the frame. In this case, monitor  12  may be constructed with a hollow lumen for passage of urine flow, and a sensor associated with monitor  12  may be oriented inward toward the lumen to sense conditions of the urine such as urodynamic conditions or urinalysis characteristics.  
       FIG. 11  is a conceptual diagram of an external controller  14  equipped to present voiding diary information to a user. External controller  14  includes a display screen  94  that presents urodynamic information associated with a particular voiding event. In the example of  FIG. 11 , display screen  94  presents the date and time  96  of the voiding event, a maximum voiding pressure  98  measured by monitor  12  during the course of the voiding event, and maximum flow rate  100  measured by monitor  12  during the course of a voiding event. A variety of additional urodynamic parameters may be presented on external controller  14 , as well as average, maximum, minimum and trend data over a voiding event or over a series of voiding events. The parameters depicted in  FIG. 11  are merely for purposes of illustration, and should not be considered limiting of the invention as broadly embodied herein.  
       FIG. 12  is another conceptual diagram of external controller  14 , illustrating organization and selection of urodynamic information obtained from monitor  12 . For example, external controller  14  may present a list  102  of voiding events throughout a period of time, such as a day or several days. If display screen  94  is equipped as a touchscreen display, or external controller  14  includes other input media, such as buttons, keys, or the like, a user may select one of the voiding events and access a set  104  of urodynamic information for the selected voiding event. The set  104  of urodynamic information, in turn, may permit the user to select individual parameters, as well as profile or trend data, for presentation on display screen  94 . External controller  14  also may provide the capability to transmit the information to another device, e.g., via wireless or wired connection.  
      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 monitor at a particular location within the urinary tract. In various embodiments, a medical device may be located anywhere within the urinary tract where useful diagnostic information can be obtained.  
      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.