fig1 is a schematic diagram illustrating an implantable stimulation system 10 for alleviation of urinary incontinence . as shown in fig1 , system 10 includes an implantable optical pressure sensor 12 , implantable stimulator 14 and external programmer 16 shown in conjunction with a patient 18 . pressure sensor 12 senses a pressure level exerted by urinary sphincter 22 on urethra 20 proximate the neck 23 of bladder 24 , and transmits pressure information based on the sensed pressure level to at least one of stimulator 14 and programmer 16 by wireless telemetry . stimulator 14 or programmer 16 may record the information , generate adjustments to electrical stimulation parameters applied by the stimulator , or both . fig2 is an enlarged schematic diagram illustrating implantable optical pressure sensor 12 . as shown in fig1 and 2 , pressure sensor 12 includes a sensor housing 26 , an optical fiber 28 , and a flexible tube section 30 . flexible tube section 30 is positioned for engagement with urinary sphincter 22 , and is sealed from the environment . tube section 30 contains a reflective , flexible diaphragm that deflects in response to pressure changes within the tube section . tube section 30 may be filled with air or other optically transmissive media . optical fiber 28 transmits light to the diaphragm and receives reflected light from the diaphragm . when the diaphragm deflects , the properties of the reflected light change , indicating a change in pressure within the flexible tube and , in turn , a change in the pressure of urinary sphincter 22 . sensor housing 26 contains a light emitter that transmits light through optical fiber 28 and a light detector that detects the reflected light received from the optical fiber , as will be described in further detail . the light emitter and detector are positioned adjacent to a proximal end of optical fiber 28 . if a single optical fiber is used for both transmission of light and reception of reflected light , an optical coupling element may be provided in sensor housing 26 to couple the emitter and detector to the optical fiber 28 . in other embodiments , separate optical fibers can be used for transmission or reception . in either case , the light detector generates an output signal that varies according to the properties of the reflected light . sensor housing 26 further includes electronics to generate pressure information based on the output signal , and telemetry circuitry for wireless transmission of the information to stimulator 14 , programmer 16 or both . as further shown in fig1 and 2 , sensor housing 26 may reside within bladder 24 . sensor housing 26 may be temporarily or permanently attached to an inner wall 27 of bladder 24 , such has the mucosal lining , as will be described . alternatively , housing 26 may be implanted sub - mucosally . optical fiber 28 extends away from sensor housing 26 and through an inner lumen defined by the bladder neck proximate urinary sphincter 22 . in this manner , flexible tube section 30 is positioned to directly sense the pressure level exerted by urinary sphincter 22 . yet , optical fiber 28 and tube section 30 may be sufficiently thin to avoid significant obstruction of urethra 20 or disruption of the function of urinary sphincter . as a further alternative , housing 26 may reside outside bladder 24 , in which case optical fiber 28 and tube section 30 may extend into bladder 24 and through urinary sphincter 22 through a hole formed in the bladder . in this case , housing 26 may be surgically or laparoscopically implanted within the abdomen . fiber 28 and tube section 30 may be surgically or laparoscopically guided through a hole in the wall of bladder 24 . a cystoscope may be used to grab tube section 30 and pull it downward through urinary sphincter 22 and urethra 20 . in some embodiments , housing 26 and its contents may be integrated with stimulator 14 , in which case optical fiber 28 and tube section 30 extends from the stimulator housing and into bladder 24 , much like leads carrying stimulation or sense electrodes with further reference to fig1 , implantable stimulator 14 includes an electrical lead 15 ( partially shown in fig1 ) carrying one or more electrodes that are placed at a nerve site within the pelvic floor . for example , the electrodes may be positioned to stimulate the sacral nerve and thereby innervate urinary sphincter 22 . in particular , electrical stimulation may be applied to cause urinary sphincter 22 to increase closing pressure to avoid involuntary leakage from bladder 24 . alternatively , if voluntary voiding is desired by patient 18 , electrical stimulation may be suspended or reduced to reduce the closing pressure exerted by urinary sphincter 22 on urethra 20 at the bladder neck . for spinal cord injury patients who cannot perceive a sensation of bladder fullness , sphincter pressure sensed by pressure sensor 12 may be transmitted to external programmer 16 , with or without an accompanying stimulator 14 , to advise the patient when urinary sphincter pressure is high , indicating bladder fullness . in this case , the advice may be in the form of a audible , visual or vibratory stimulus . in response to the advice , the spinal cord injury patient is able to catheterize the urethra 20 and bladder 24 to voluntarily relieve urine . implantable stimulator 14 delivers stimulation therapy to the sacral nerve in order to keep the sphincter 22 constricted and keep contents of bladder 24 from leaking out through urethra 20 . at predetermined times or at patient controlled instances , the external programmer 16 may program stimulator 14 to interrupt the stimulation to allow the sphincter to relax , thus permitting voiding of bladder 24 . upon completion of the voiding event , external programmer 16 may program stimulator 14 to resume stimulation therapy and thereby maintain closure of urinary sphincter 22 . in addition , adjustment of stimulation parameters may be responsive to pressure information transmitted by implantable optical pressure sensor 12 . for example , external programmer 16 or implantable stimulator 14 may adjust stimulation parameters , such as amplitude , pulse width , and pulse rate , based on pressure information received from implantable sensor 12 . in this manner , implantable stimulator 14 adjusts stimulation to either increase or reduce urinary sphincter pressure based on the actual pressure level exerted by urinary sphincter 22 . pressure sensor 12 may transmit pressure information periodically , e . g ., every few seconds , minutes or hours . in some embodiments , pressure sensor 12 may transmit pressure information when there is an abrupt change in sphincter pressure , e . g ., a pressure change that exceeds a predetermined threshold . in addition to parameter adjustments , or alternatively , adjustment may involve on and off cycling of the stimulation in response to pressure levels indicative of a particular bladder fill stage . for example , stimulation may be turned off until the pressure level exceeds a threshold indicative of a particular fill stage of the bladder , at which time stimulation is turned on . then , stimulation parameters may be further adjusted as the sensed pressure level changes . external programmer 16 may be a small , battery - powered , portable device that accompanies the patient 18 throughout a daily routine . programmer 16 may have a simple user interface , such as a button or keypad , and a display or lights . patient 18 may initiate a voiding event , i . e ., a voluntary voiding of bladder 24 , via the user interface . in some embodiments , the length of time for a voiding event may be determined by pressing and holding down a button for the duration of a voiding event , pressing a button a first time to initiate voiding and a second time when voiding is complete , or by a predetermined length of time permitted by programmer 16 or implantable stimulator 14 . in each case , programmer 16 causes implantable stimulator 14 to temporarily terminate stimulation so that voluntary voiding is possible . in some embodiments , stimulator 14 may immediately recommence stimulation upon completion of a voiding event , and thereafter adjust stimulation parameters based on pressure information generated by implantable sensor 12 . alternatively , stimulator 14 may terminate stimulation upon initiation of a voiding event , and recommence stimulation only after implantable pressure sensor 12 measures a decrease of pressure in the urethra 20 that corresponds to bladder 24 being empty . as a further alternative , following completion of the voiding event , stimulator 14 may wait to recommence stimulation until pressure sensor 12 detects generation of an inadequate pressure level by urinary sphincter 22 , which could result in involuntary leakage . in this case , stimulator 14 recommences stimulation to enhance urinary sphincter pressure . implantable stimulator 14 may be constructed with a biocompatible housing , such as titanium or stainless steel , or a polymeric material such as silicone or polyurethane , and surgically implanted at a site in patient 18 near the pelvis . the implantation site may be a subcutaneous location in the side of the lower abdomen or the side of the lower back . one or more electrical stimulation leads 15 are connected to implantable stimulator 14 and surgically or percutaneously tunneled to place one or more electrodes carried by a distal end of the lead at a desired nerve site , such as a sacral nerve site within the sacrum . in the example of fig1 and 2 , sensor housing 26 of implantable pressure sensor 12 is attached to the inner wall 27 of bladder 24 near bladder neck 23 . however , the attachment site for sensor housing 26 could be anywhere with access to urinary sphincter 22 . with a relatively long optical fiber 28 , for example , sensor housing 26 could be positioned at a greater distance from bladder neck 23 . also , in some embodiments , sensor housing 26 could be attached within urethra 20 , e . g ., downstream from urinary sphincter 22 , although attachment of the sensor housing within bladder 24 may be desirable to avoid obstruction of the urethra . fig3 is an enlarged , cross - sectional side view of the implantable pressure sensor 12 of fig1 and 2 . as shown in fig3 , sensor housing 26 receives the proximal end of flexible optical fiber 28 . a sensing element 34 is mounted within sensor housing 26 to sense a urinary sphincter pressure level via optical fiber 28 . sensing element 34 may be coupled to a circuit board 38 within sensor housing 26 , and includes an optical emitter 35 and a detector 37 . optical emitter 35 may be a light emitting diode ( led ). detector 37 may be a photodiode . in the example of fig3 , optical fiber 28 includes two optical fibers , i . e ., a transmit fiber 39 coupled to emitter 35 and a receive fiber 41 coupled to optical detector 41 . each optical fiber 39 , 41 extends into flexible tube section 30 . sensor housing 26 may be made from a biocompatible material such as titanium , stainless steel or nitinol , or a polymeric material such as silicone or polyurethane . another material for fabrication of sensor housing 26 is a two - part epoxy . an example of a suitable epoxy is a two - part medical implant epoxy manufactured by epoxy technology , inc ., mixed in a ratio of 10 grams of resin to one gram of activator . in general , sensor housing 26 contains no external openings , with the exception of the opening to receive optical fiber 28 , thereby protecting sensing element 26 and circuit board 38 from the environment within bladder 24 . the proximal end of optical fiber 28 resides within sensor housing 26 while the distal end resides outside of the sensor housing . the opening in sensor housing 26 that receives the proximal end of optical fiber 28 may be sealed to prevent exposure of interior components . the core and cladding of optical fiber 28 may be formed from any of a variety of conventional glass or polymeric materials . in addition , single mode or multi - mode fibers may be selected . in some embodiments , a protective , a flexible sheath ( not shown ) may be formed over optical fiber 28 . the flexibility of optical fiber 28 permits it to bend and conform to contours within bladder neck 23 , facilitating placement of flexible tube section 30 within urethra 20 proximate urinary sphincter 22 . flexible tube section 30 may be formed from any of a variety of flexible , biocompatible materials such as polyurethane or silicone . the material should be sufficiently flexible to permit deform in response to pressure exerted on urethra 20 by urinary sphincter 22 at bladder neck 23 . flexible tube section 30 preferably is sealed to define a compartment . so that deformation produces volumetric changes and pressure changes within the compartment . accordingly , flexible tube section 30 may have a closed distal end and a sealed proximal end that is sealed about fiber 28 . the compartment may contain a gaseous medium such as air . during operation , urinary sphincter 22 exerts pressure inward against the outer wall of urethra 20 . in turn , the inner wall of urethra 20 exerts pressure inward against the outer wall of flexible tube section 30 , causing the wall of the tube section to deform and compress inward . in some embodiments , flexible tube section 30 may be coated to avoid calcification . inward deformation of flexible tube section 30 causes a mechanical deflection of the membrane mounted inside . as light is transmitted onto the membrane by optical fiber 39 , some of the reflected light received by optical fiber 41 is refracted to a varying degree based upon the deformation of the membrane . when the reflected light is detected by light detector 37 , the light detector generates an output signal that is influenced by the physical properties of the detected light . circuitry within sensing element generates pressure information based on the reflected light detected by detector 37 . the physical property may be simply an intensity of the received light , which is influenced by the degree of deflection of the membrane . in this case , an increase or decrease in the intensity of reflected light can be use to produce a urinary sphincter pressure level . alternatively , physical property may be a wavelength of the reflected light , relative to a wavelength of the transmitted light . as the membrane deflects , changes in the wavelength of the reflected light can be used to produce a urinary sphincter pressure level . in other embodiments , the membrane may be formed with an interference pattern or grating that aids in wavelength differentiation between the reflected light and the transmitted light . based upon the differences in amplitude , wavelength , or other optical properties , sensing element 34 generates a pressure signal that represents the pressure on flexible tube section 30 . electronics on circuit board 38 generate pressure information based on the pressure signal . optical fiber 28 and flexible tube section 30 may be provided with different dimensions selected for patients having different anatomical dimensions . in particular , implantable pressure sensor 12 may be constructed with an optical fiber 28 and flexible tube section 30 having different lengths and diameters . different tube lengths may be necessary given the distance between the attachment site of sensor housing 26 and urinary sphincter 22 , either to ensure that flexible tube section 30 reaches the sphincter or does not extend too far down urethra 20 . multiple diameters may also be necessary to allow a dysfunctional sphincter 22 to close completely or to allow optical fiber 28 and flexible tube section 30 to be placed into a narrow urethra 20 . the dimensions may be fixed for a given pressure sensor 12 , as a complete assembly . alternatively , fluid tubes of different sizes may be attached to a pressure sensor housing 26 by a physician prior to implantation . in general , for male patients , optical fiber 28 and tube section 30 may have a combined length of less than approximately 9 cm and more preferably less than approximately 7 cm . for female patients , optical fiber 28 and tube section 30 may have a combined length f less than approximately 7 cm and more preferably less than approximately 5 cm . in some embodiments , optical fiber 28 and tube section 30 may have a combined length of approximately 0 . 5 cm to 3 cm . the length of optical fiber 28 and tube section 30 may vary according to the anatomy of the patient , and may vary between male , female and pediatric patients . in addition , tube 30 may have an outer diameter in a range of approximately 1 to 3 mm . the wall of tube 30 may be relatively thin to ensure sufficient deformation and conformability , yet thick enough to ensure structural integrity . as an example , the thickness of the wall of tube 30 may be in a range of approximately 0 . 1 mm to 0 . 3 mm . attaching implantable pressure sensor 12 to the mucosal lining of bladder 24 may be accomplished in a variety of ways , but preferably is completed in a manner that will not excessively injure bladder 24 . preferably , attachment should cause limited inflammation no adverse physiological modification , such as tissue infection or a loss in structural integrity of bladder 24 . however , it is desirable that implantable pressure sensor 12 also be attached securely to the attachment site in order to provide an extended period of measurement without prematurely loosening or detaching from the intended location . as an example , sensor housing 26 may contain a vacuum cavity 39 that permits a vacuum to be drawn by a vacuum channel 40 . the vacuum is created by a deployment device having a vacuum line in communication with vacuum channel 40 . the vacuum draws a portion 42 of the mucosal lining 44 of bladder 24 into vacuum cavity 39 . once the portion 42 of mucosal lining 44 is captured within vacuum cavity 39 , a fastening pin 46 is driven into the captured tissue to attach sensor housing 26 within bladder 24 . fastening pin 46 may be made from , for example , stainless steel , titanium , nitinol , or a high density polymer . the shaft of pin 46 may be smooth or rough , and the tip may be a sharp point to allow for easy penetration into tissue . fastening pin 46 may be driven into housing 26 and the portion 42 of mucosal lining 44 under pressure , or upon actuation by a push rod , administered by a deployment device . in some embodiments , fastening pin 46 may be manufactured from a degradable material that the breaks down over time , e . g . in the presence of urine , to release implantable pressure sensor 12 within a desired time period after attachment . in still another embodiment , implantable pressure sensor 12 may be attached without the use of a penetrating rod but with a spring - loaded clip to pinch trapped mucosal lining 44 within cavity 39 . a variety of other attachment mechanisms , such as pins , clips , barbs , sutures , helical screws , surgical adhesives , and the like may be used to attach sensor housing 26 to mucosal lining 44 of bladder 24 . fig4 is a schematic diagram illustrating placement of an implantable pressure sensor 12 with a flexible optical fiber 28 extending through the urinary sphincter 22 of a patient 18 . fig4 also illustrates flexible tube section 30 in greater detail . in the example of fig4 , optical fiber 28 , including transmit fiber 39 and receive fiber 41 , leaves bladder 24 through bladder neck 23 and passes through internal urinary sphincter 22 as it enters urethra 20 . in general , sphincter 22 is an annulus shaped muscle that surrounds the portion of urethra 20 below bladder neck 23 and constricts to make the urethral walls meet and thereby close urethra 20 to prevent involuntary urine leakage from bladder 24 . upon constriction of sphincter 22 , the walls of urethra 20 close onto flexible tube section 30 of optical fiber 28 to increase the internal pressure of the tube section , which provides a measurement of the closing pressure of sphincter 22 . as further shown in fig4 , flexible diaphragm 43 is mounted within flexible tube section 30 below optical fibers 39 , 41 . flexible diaphragm 43 includes an optically reflective surface on a side facing optical fibers 39 , 41 . in this manner , light transmitted via optical fiber 39 is reflected by diaphragm 43 and received via optical fiber 41 . flexible diaphragm may be substantially circular and bonded at its edges to an inner wall of flexible tube section 30 . for example , flexible diaphragm may be bonded to the inner wall of flexible tube section 30 by adhesives , ultrasonic welding , or other techniques . in some embodiments , tube section 30 may include an annular mounting ledge or other equivalent mounting structures to support at least an outer edge of the diaphragm 43 . flexible diaphragm 43 may be formed from any of a variety of flexible materials . the materials may be reflective . alternatively , a reflective coating may be formed on diaphragm 43 , e . g ., by vapor deposition , sputtering , dip coating , roll coating or the like . because optical fiber 28 and flexible tube section 30 have circular cross - sections and a small diameter , a closed sphincter 22 will still be able to substantially seal urethra 20 around optical fiber 28 , flexible tube section 30 , or both . when sphincter 22 is relaxed , in some embodiments , implantable pressure sensor 12 may be used to measure the pressure of fluid in urethra 20 . the open sphincter 22 allows urine to be passed out of the urethra and patient 18 . optical fiber 28 is under the same pressure as the urethra and can allow implantable pressure sensor 12 to measure this urethral pressure . this may allow monitoring of urinary dysfunctions due to pressure during voiding events and may also be used by implantable stimulator 14 to detect the end of a voiding event by measuring decrease of urethral pressure as an indication of reduced urine flow . as shown in fig4 , the placement of optical fiber 28 and flexible tube section 30 does not significantly interfere with normal bladder function . bladder function is unimpaired and fluid flow to urethra 20 can occur normally , as flexible tube section 30 allows enough room for urine to pass and exit bladder 24 via urethra 20 . due to varying sizes and shapes of patient anatomy , optical fiber 28 and flexible tube section 30 may be manufactured in a variety of lengths and diameters . fig5 is functional block diagram illustrating various components of an exemplary implantable pressure sensor 12 . in the example of fig5 , implantable pressure sensor 12 includes a sensing element 34 , processor 48 , memory 50 , telemetry interface 52 , and power source 54 . sensing element 34 transforms measured changes in emitted light from optical fiber 28 into electrical signals representative of closing pressure of urinary sphincter 22 . again , optical fiber 28 may include a transmit fiber 39 and a receive fiber 41 , or a single fiber with an optical coupler for optical coupling to emitter 35 and detector 37 . the electrical signals may be amplified , filtered , and otherwise processed as appropriate by electronics within sensor 12 . in particular , sensor 12 may include circuitry to detect changes in light intensity or wavelength . in some embodiments , the signals may be converted to digital values and processed by processor 48 before being saved to memory 50 or sent to implantable stimulator 14 as pressure information via telemetry interface 52 . memory 50 stores instructions for execution by processor 48 and pressure information generated by sensing element 36 . pressure data may then be sent to implantable stimulator 14 or external programmer 16 for long - term storage and retrieval by a user . memory 50 may include separate memories for storing instructions and pressure information . in addition , processor 48 and memory 50 may implement loop recorder functionality in which processor 48 overwrites the oldest contents within the memory with new data as storage limits are met , thereby conserving memory space . processor 48 controls telemetry interface 52 to send pressure information to implantable stimulator 14 or programmer 16 on a continuous basis , at periodic intervals , or upon request from the implantable stimulator or programmer . wireless telemetry may be accomplished by radio frequency ( rf ) communication or proximal inductive interaction of pressure sensor 12 with programmer 16 . power source 54 delivers operating power to the components of implantable pressure sensor 12 . power source 54 may include a battery and a power generation circuit to produce the operating power . in some embodiments , the battery may be rechargeable to allow extended operation recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within sensor 12 . in some embodiments , power requirements may be small enough to allow sensor 12 to utilize patient motion and implement a kinetic energy - scavenging device to trickle charge a rechargeable battery . in other embodiments , traditional batteries may be used for a limited period of time . as a further alternative , an external inductive power supply could transcutaneously power sensor 12 whenever pressure measurements are needed or desired . fig6 is a functional block diagram illustrating various components of an implantable stimulator 14 . in the example of fig6 , stimulator 14 includes a processor 56 , memory 58 , stimulation pulse generator 60 , telemetry interface 62 , and power source 64 . memory 58 stores instructions for execution by processor 56 , stimulation therapy data , and pressure information received from pressure sensor 12 via telemetry interface . pressure information is received from pressure sensor 12 and may be recorded for long - term storage and retrieval by a user , or adjustment of stimulation parameters , such as amplitude , pulse width or pulse rate . memory 58 may include separate memories for storing instructions , stimulation parameter sets , and pressure information . processor 56 controls stimulation pulse generator 60 to deliver electrical stimulation therapy and telemetry interface 62 to send and receive information . an exemplary range of neurostimulation stimulation pulse parameters likely to be effective in treating incontinence , e . g ., when applied to the sacral or pudendal nerves , are as follows : 1 . frequency : between approximately 0 . 5 hz and 500 hz , more preferably between approximately 5 hz and 250 hz , and still more preferably between approximately 10 hz and 50 hz . 2 . amplitude : between approximately 0 . 1 volts and 50 volts , more preferably between approximately 0 . 5 volts and 20 volts , and still more preferably between approximately 1 volt and 10 volts . 3 . pulse width : between about 10 microseconds and 5000 microseconds , more preferably between approximately 100 microseconds and 1000 microseconds , and still more preferably between approximately 180 microseconds and 450 microseconds . based on pressure information received from sensor 12 , processor 56 interprets the information and determines whether any therapy parameter adjustments should be made . for example , processor 56 may compare the pressure level to one or more thresholds , and then take action to adjust stimulation parameters based on the pressure level . information may be received from sensor 12 on a continuous basis , at periodic intervals , or upon request from stimulator 14 or external programmer 16 . alternatively , or additionally , pressure sensor 12 may transmit pressure information when there is an abrupt change in the pressure level , e . g ., at the onset of involuntary leakage . in addition , processor 56 modifies parameter values stored in memory 58 in response to pressure information from sensor 12 , either independently or in response to programming changes from external programmer 16 . stimulation pulse generator 60 provides electrical stimulation according to the stored parameter values via a lead 15 implanted proximate to a nerve , such as a sacral nerve . processor 56 determines any parameter adjustments based on the pressure information obtained form sensor 12 , and loads the adjustments into memory 58 for use in delivery of stimulation . as an example , if the pressure information indicates an inadequate sphincter closing pressure , processor 56 may increase the amplitude , pulse width or pulse rate of the electrical stimulation applied by stimulation pulse generator 60 to increase stimulation intensity , and thereby increase sphincter closing pressure . if sphincter closing pressure is adequate , processor 56 may implement a cycle of downward adjustments in stimulation intensity until sphincter closing pressure becomes inadequate , and then incrementally increase the stimulation upward until closing pressure is again adequate . in this way , processor 56 converges toward an optimum level of stimulation . although processor 56 is described in this example as adjusting stimulation parameters , it is noted that the adjustments may be generated by external programmer 16 . the adequacy of closing pressure is determined by reference to the pressure information obtained from sensor 12 . sphincter pressure may change due to a variety of factors , such as an activity type , activity level or posture of the patient 18 . hence , for a given set of stimulation parameters , the efficacy of stimulation may vary in terms of sphincter pressure , due to changes in the physiological condition of the patient . for this reason , the continuous or periodic availability of pressure information from implantable sensor 12 is highly desirable . with this pressure information , stimulator 14 is able to respond to changes in sphincter pressure with dynamic adjustments in the stimulation parameters delivered to the patient 18 . in particular , processor 56 is able to adjustment parameters in order to cause constriction of sphincter 22 and thereby avoid involuntary leakage . in some cases , the adjustment may be nearly instantaneous , yet prevent leakage . as an example , if patient 18 laughs , coughs , or bends over , the resulted force on bladder 24 could overcome the closing pressure of urinary sphincter 22 . if pressure sensor 12 indicates an abrupt change in sphincter pressure , however , stimulator 14 can quickly respond by more vigorously stimulating the sacral nerves to increase sphincter closing pressure . in general , if sphincter 22 is not constricting enough to effectively close urethra 20 , processor 56 may dynamically increase the level of therapy to be delivered . conversely , if sphincter 22 is consistently achieving effective constriction , processor 56 may incrementally reduce stimulation , e . g ., to conserve power resources . as in the case of sensor 12 , wireless telemetry in stimulator 14 may be accomplished by radio frequency ( rf ) communication or proximal inductive interaction of pressure stimulator 14 with implantable pressure sensor 12 or external programmer 16 . accordingly , telemetry interface 62 may be similar to telemetry interface 52 . also , power source 64 of stimulator 14 may be constructed somewhat similarly to power source 54 . for example , power source 64 may be a rechargeable or non - rechargeable battery , or alternatively take the form of a transcutaneous inductive power interface . fig7 is a schematic diagram illustrating cystoscopic deployment of an implantable pressure sensor 12 via the urethra 20 using a deployment device 66 . pressure sensor 12 may be surgically implanted . however , cystoscopic implantation via urethra is generally more desirable in terms of patient trauma , recovery time , and infection risk . in the example of fig7 , deployment device 66 includes a distal head 68 , a delivery sheath 69 and a control handle 70 . deployment device 66 may be manufactured from disposable materials for single use applications or more durable materials for multiple applications capable of withstanding sterilization between patients . as shown in fig7 , distal head 68 includes a cavity that retains sensor housing 26 of implantable pressure sensor 12 for delivery to a desired attachment site within bladder 24 . sensor housing 26 may be held within cavity 72 by a friction fit , vacuum pressure , or a mechanical attachment . in each case , once distal head 68 reaches the attachment site , sensor housing 26 may be detached . sheath 69 is attached to distal head 68 and is steerable to navigate urethra 20 and guide the distal head into position . in some embodiments , sheath 69 and distal head 68 may include cystoscopic viewing components to permit visualization of the attachment site . in other cases , external visualization techniques such as ultrasound may be used . sheath 68 may include one or more steering mechanisms , such as wires , shape memory components , or the like , to permit the distal region adjacent distal head 68 to turn abruptly for access to the mucosal lining of bladder 24 . a control handle 70 is attached to sheath 69 to aid the physician in manually maneuvering deployment device 66 throughout urethra 20 and bladder 24 . control handle 70 may have a one or more controls that enable the physician to contort sheath 69 and allow for deployment device 66 to attach pressure sensor housing 26 to the mucosal lining of bladder 24 and then release the sensor housing to complete implantation . a vacuum source 74 supplies negative pressure to a vacuum line within sheath 69 to draw tissue into the vacuum cavity defined by sensor housing 66 . a positive pressure source 76 supplies positive pressure to a drive a fastening pin into the tissue captured in the vacuum cavity . deployment device 66 enters patient urethra 20 to deliver pressure sensor 12 and implant it within bladder 24 . first , the physician must guide distal head 68 through the opening of urethra 20 in patient 18 . second , distal head 68 continues to glide up urethra 20 and past the relaxed internal sphincter 22 . distal head 300 is then pushed through bladder neck 23 and into bladder 24 , for access to an appropriate site to attach pressure sensor 12 . using actuators built into control handle 70 , sheath 69 is bent to angle distal head 68 into position . again , sheath 69 may be steered using control wires , shape memory alloys or the like . as pressure sensor 12 is guided into place against the mucosal wall 44 of bladder 24 , a physician actuates control handle 70 to attach sensor 12 to mucosal wall 44 and then release the attached sensor . upon attachment , pressure sensor 12 is implanted within bladder 24 of patient 18 and deployment device 66 is free to exit the bladder . exemplary methods for attachment and release of sensor 12 , including the use of both vacuum pressure and positive pressure , will be described in greater detail below . although fig7 depicts cystoscopic deployment of pressure sensor 12 , surgical or laparoscopic implantation techniques alternatively may be used . fig8 is a schematic diagram illustrating retraction of deployment device 66 upon fixation of pressure sensor 12 within the urinary tract of patient 18 . once the sensor 12 is released , optical fiber 28 remains attached to sensor housing 26 . during removal of deployment device 66 , optical fiber 28 and flexible tube section 30 maintain position within bladder neck 23 adjacent sphincter 22 . as deployment device 66 is removed , optical fiber 28 and flexible tube section 30 pass through a guide channel formed in the deployment device . the guide channel ensures that optical fiber 28 and flexible tube section 30 remain pinned between distal head 68 and the wall of bladder 24 . as distal head 68 slides through sphincter 22 and urethra 20 , however , optical fiber 28 releases from deployment device 66 and is left in place within the urethra in the region proximate urinary sphincter 22 . deployment device 66 may then be completely withdrawn past the external urinary sphincter and out of the remainder of urethra 20 . in the example of fig8 , optical fiber 28 is suspended by device housing 26 , which is attached to mucosal wall 44 , and is held in place by pressure exerted against the urethral wall by urinary sphincter 22 . in other embodiments , optical fiber 28 and flexible tube section 30 may be kept in place using other techniques such as actively fixing optical fiber 28 or tube section 30 to the side of urethra 20 , e . g ., with sutures or other anchor mechanisms . in a preferred embodiment , sheath 69 and distal head 68 may be disposable . disposable devices that come into contact with patient 18 tissues and fluids greatly decrease the possibility of infection in implantable devices . control handle 70 does not come into contact with body fluids of patient 18 and may be used for multiple patients . in another embodiment , the entire deployment device 66 may be manufactured out of robust materials intended for multiple uses . the device would then need to be sterilizable between uses . in still a further embodiment , the features of distal head 68 may be incorporated into pressure sensor 12 . in this configuration , pressure sensor 12 may be larger in size but would include the necessary elements for attachment within the device . after attachment , the entire sensor would detach from sheath 69 , making removal of deployment device 66 easier on patient 18 . after the useful life of implantable pressure sensor 12 is complete or it is no longer needed within patient 18 , it can be removed from patient 18 in some manner . as an example , deployment device 66 may be reinserted into patient 18 , navigated into bladder 24 , and reattached to pressure sensor 12 . deployment device 66 may then be withdrawn from the bladder 24 and urethra 20 , explanting sensor 12 , including housing 26 and optical fiber 28 , from patient 18 . in another embodiment , as mentioned with respect to fig3 , the attachment method of pressure sensor 12 to bladder 24 may involve degradable materials , such as a biodegradable fixation pin . after a certain period of time exposed to urine in the bladder 24 , the fixation material may structurally degrade and allow pressure sensor 12 to be released from the mucosal wall 44 of bladder 24 . in some embodiments , sensor 12 may be sized sufficiently small to follow urine out of the bladder , urethra , and body during a voiding event . in other embodiments , sensor housing 26 or tube section 30 may carry a suture - like loop that can be hooked by a catheter with a hooking element to withdraw the entire assembly from patient 18 via urethra 20 . in still further embodiments , such a loop may be long enough to extend out of the urethra , so that the loop can be grabbed with an external device or the human hand to pull the sensor 12 out of the patient . fig9 is a cross - sectional side view of distal head 68 of deployment device 66 during deployment and fixation of pressure sensor 12 . in the example of fig9 , distal head 68 a vacuum line 78 and a positive pressure line 80 . vacuum line 78 is coupled to vacuum source 74 via a tube or lumen extending along the length of sheath 69 . similarly , positive pressure line 80 is coupled to positive pressure source 76 via a tube or lumen extending along the length of sheath 69 . vacuum line 78 is in fluid communication with vacuum cavity 39 , and permits the physician to draw a vacuum and thereby capture a portion 42 of mucosal lining 44 within the vacuum cavity . positive pressure line 80 permits the physician to apply a pulse of high pressure fluid , such as a liquid or a gas , to drive fixation pin 46 into sensor housing 26 and through the portion 42 of mucosal lining 44 . pin 46 thereby fixes sensor housing 26 to mucosal lining 44 . in some embodiments , a membrane mounted over an opening of positive pressure line 80 may be punctured by pin 46 . optical fiber 28 resides within a channel of sheath 69 prior to detachment or sensor 12 from distal head 68 . once fixation pin 46 attaches sensor 12 to bladder 24 , vacuum line 78 is no longer needed . however , in some embodiments , vacuum line 78 may be used to detach pressure sensor 12 from distal head 68 of deployment device 66 . by terminating vacuum pressure , or briefly applying positive pressure through vacuum line 78 , for example , head 68 may separate from sensor 12 due to the force of the air pressure . in this manner , vacuum line 78 may aid in detachment of sensor 12 prior to withdrawal of deployment device 66 . as described previously in fig3 , fixation pin 46 punctures mucosal lining 44 for fixation of sensor 12 . while the force of this fixation may vary with patient 18 , deployment device 66 provides adequate force for delivery of pin 46 . in an exemplary embodiment , positive pressure line 80 is completely sealed and filled with a biocompatible fluid , such as water , saline solution or air . sealing the end of positive pressure line 80 is a head 82 on fixation pin 46 . head 82 is generally able to move within positive pressure line 80 much like a piston . force to push fixation pin 46 through the portion 42 of mucosal lining 44 captured in vacuum cavity 39 is created by application of a pulse of increased fluid pressure within positive pressure line 80 . for example , the physician may control positive pressure source 76 via control handle 70 . this simple delivery method may provide high levels of force , allow multiple curves and bends in articulating arm 306 , and enable a positive pressure line 80 of many shapes and sizes . in an alternative embodiment , a flexible , but generally incompressible , wire may placed within positive pressure line 80 and used to force fixation pin 46 through the captured portion 42 of mucosal lining 44 . this wire presents compressive force from control handle 70 directly to the head 82 of fixation pin 46 . this method may eliminate any safety risk of pressurized fluids entering patient 18 or , in some embodiments , permit retraction of pin 46 after an unsuccessful fixation attempt . the flexible wire may be attached to pin 46 and pulled back to remove the pin from capture mucosal tissue 42 . the flexible wire may be sheared from fixation pin 46 for detachment purposes as distal head 68 releases sensor 12 . this detachment may be facilitated by a shearing element or simply low shear stress of the wire enables separation when distal head 68 slides past pin 46 . in fig9 , deployment device 66 illustrates optical fiber 28 on the same end of housing 26 as sheath 69 , while the fixation structures are located in the opposite , or distal end of distal head 68 . in some embodiments , it may be necessary for pressure sensor 12 to be deployed with tube section 30 located at the distal end of head 68 and the fixation structures located near sheath 69 . in still other embodiments , the fixation structures and tube section 30 may be located on the same end of pressure sensor 12 . in some embodiments , deployment device 66 may include a small endoscopic camera in the distal head 68 . the camera may enable the physician to better guide deployment device 66 through urethra 20 , past sphincter 22 , and to a desired attachment location of bladder 24 in less time with more accuracy . images may be displayed using video fed to a display monitor . fig1 is a cross - sectional bottom view of the deployment device 66 of fig1 before attachment of pressure sensor 12 . as shown in fig1 , distal head 68 includes proximal tube channel 84 to accommodate optical fiber 28 during placement of sensor 12 and distal tube channel 86 to accommodate the flexible tube during retraction of deployment device 66 . in addition , sheath 69 includes a sheath channel 88 to accommodate optical fiber 28 and flexible tube section 30 . channels 84 , 86 , 88 serve to retain tube section 30 during delivery of sensor 12 to an attachment site . note that the channels are larger than the shown portion of optical fiber 28 to enable the passage of the larger perturbation section 30 of optical fiber 28 . in some embodiments , tube section 30 may be of similar diameter to optical fiber 28 . distal head 68 is rounded on both sides at the distal end to permit easier entry of deployment device into areas of patient 18 . head 68 may also be lubricated before delivery to facilitate ease of navigation . on the proximal end of head 68 , proximal tube channel 84 runs through the head for unimpeded removal of optical fiber 28 and tube section 30 during detachment of pressure sensor 12 . this channel may be u - shaped , e . g . closed on 3 sides . in some embodiments , proximal tube channel 84 may be an enclosed hole in which optical fiber 28 resides and glides through upon deployment device 30 removal . sheath channel 88 is formed within sheath 69 to allow optical fiber 28 to stay in place during delivery of pressure sensor 12 . in this embodiment , optical fiber 28 is only partially retained within channel 88 . in some embodiments , sheath channel 88 may be deeper to allow optical fiber 28 to lie completely within sheath 69 , whereas others may include a completely enclosed channel out of which optical fiber 28 glides after attachment . distal channel 86 in distal end of head housing 68 is not used by optical fiber 28 before attachment . the purpose of this open channel is to allow optical fiber 28 and flexible tube section 30 to glide through it while head 68 is removed from bladder 24 . as head 68 slides back past pressure sensor 12 , optical fiber 28 and tube section 30 will slide through channel 86 and head housing 68 will keep optical fiber 28 and tube section 30 between the wall of bladder 24 and head 68 until head 68 has been removed beyond sphincter 22 . optical fiber 28 and tube section 30 may then be ensured correct placing through sphincter 22 . some embodiments of optical fiber 28 and flexible tube section 30 include multiple length and diameter combinations which would lead to modifications in channels 84 , 86 and 88 . these channels may be of different diameters or lengths to properly house optical fiber 28 , tube section 30 , or both . one embodiment may include flexible housing channels to accommodate a wide variety of dimensions . further embodiments of deployment device 30 may contain modified channel locations in head housing 68 . these locations may be needed to place optical fiber 28 and flexible tube section 30 in different locations , particularly at different sphincter sites as in some embodiments . fig1 is a flow diagram illustrating a technique for delivery of stimulation therapy based on closed loop feedback from an implantable pressure sensor . in the example of fig1 , implantable stimulator 14 requires information from implantable pressure sensor 12 and external programmer 16 . the flow of events begins with implantable stimulator 14 communicating with implantable pressure sensor 12 and sending a command to sense the pressure of sphincter 22 ( 90 ). the pressure sensor 12 subsequently acquires a pressure measurement and delivers the data to implantable stimulator 14 ( 92 ). upon receiving the pressure data , implantable stimulator 14 calibrates the data and compares it to a determined minimum pressure threshold ( 94 ). if the measured pressure is higher than the threshold , the loop begins again . if the pressure is lower than the threshold , the flow continues to the next step of stimulation . implantable stimulator 14 communicates with external programmer 16 to check if patient 18 has desired to void the contents of bladder 24 ( 96 ). if patient 18 has signaled a voiding event , stimulation is skipped and the process begins again . in the case of no voiding event desired , sphincter 22 is not providing adequate closing pressure and needs to be stimulated , or more vigorously stimulated . implantable stimulator 14 next performs the necessary tasks to adjust a level of stimulation for stimulation pulse generator 60 ( 98 ). stimulator 14 concludes the loop by delivering electric stimulation thereby to a nerve that innervates sphincter 22 ( 100 ). after stimulation therapy has commenced , the loop begins again to continue appropriate therapy to patient 18 . in some embodiments , pressure sensor 12 may be used exclusively for monitoring pressure without providing feedback for stimulation therapy . in this case , the logic loop would be much simpler and only include collecting data and sending it to an external programmer ( 90 and 92 ). pressure may be measured continuously , intermittently or at the request of external programmer 16 . these embodiments may be used for disease diagnosis or condition monitoring and may provide a patient to avoid frequent clinic visits and uncomfortable procedures . in some embodiments , the pressure measurements may form part of an automated voiding diary that records voluntary voiding events , involuntary voiding events , and urinary sphincter and urethral pressure levels prior to , contemporaneous with , of after such an event . although the invention may be especially applicable to sensing urinary sphincter pressure , the invention alternatively may be applied more generally to other sphincters within the patient , such as the lower esophageal sphincter ( les ) or pyloric sphincter . in addition , in those instances , the invention may be adapted to support electrical stimulation of other body organs , such as the stomach or intestines , e . g ., for treatment of obesity or gastric mobility disorders . not only may stimulation of certain nerves allow for the proper closure of a sphincter , but nerve stimulation may be able to modify stomach contractions or intestinal contractions based upon pressure measurements at those sites . pressure feedback from the implantable pressure sensor may be the most effective therapy for some patients , e . g ., in the form of biofeedback that aids the patient in self - regulating bladder control . also , the invention need not be limited to neurostimulation , and may be applied to stimulate other tissue , including muscle tissue . various embodiments of the described invention may include processors that are realized by microprocessors , application - specific integrated circuits ( asic ), field - programmable gate arrays ( fpga ), or other equivalent integrated or discrete logic circuitry . the processor may also utilize several different types of data storage media to store computer - readable instructions for device operation . these memory and storage media types may include any form of computer - readable media such as magnetic or optical tape or disks , solid state volatile or non - volatile memory , including random access memory ( ram ), read only memory ( rom ), electronically programmable memory ( eprom or eeprom ), or flash memory . each storage option may be chosen depending on the embodiment of the invention . while the implantable stimulator and implantable pressure sensor ordinarily will contain permanent memory , a patient or clinician programmer may contain a more portable removable memory type to enable easy data transfer for offline data analysis . many embodiments of the invention have been described . various modifications may be made without departing from the scope of the claims . for example , although the invention has been generally described in conjunction with implantable neurostimulation devices , a flexible tube sensor may also be used with other implantable medical devices , such as electrical muscle stimulation devices , functional electrical stimulation ( fes ) devices , and implantable drug delivery devices , each of which may be configured to treat incontinence or other conditions or disorders . these and other embodiments are within the scope of the following claims .
the disclosure describes an optical fiber pressure sensor to measure sphincter pressure which may be incorporated into a therapeutic sphincter control system . the system senses sphincter pressure and sends the information to a stimulator that is capable of stimulation therapy to control sphincter contractility , thus reducing unwanted urinary incontinence . measuring sphincter pressure is accomplished through the use of an optical fiber connected to flexible tube section placed through the sphincter , where properties of the emitted light are changed proportional to the pressure on the tube section . the light is returned to a light detector to measure light properties and create an electrical signal representative of the pressure on the tube section . the signal may then be sent by wireless telemetry to an implanted stimulator or external programmer .