WO2004037082A1 - Anatomical sensor - Google Patents

Abstract

An anatomical sensor (10) comprising a transducer having a structure formed by at least one elongate sensor element (11) and attachable against an anatomical part of a human or animal, wherein by linear elongation and contraction the sensor element (11) electrically detects relative changes in dimension or configuration of the anatomical part; and a measurement circuit connected to the transducer captures electric signals from the transducer for processing.

Description

ANATOMICAL SENSOR

The present invention relates to an anatomical sensor that detects relative changes in the dimension and configuration of an anatomical part of a human or animal. The sensor is preferably used to distinguish and monitor real or apparent volume changes of a mammalian bladder.

BACKGROUND TO THE INVENTION

The urinary bladder is composed in large part of smooth muscle cells collectively referred to as the detrusor muscle. As the normal bladder fills with urine, the detrusor muscle progressively relaxes to permit expansion of the bladder's volume without any significant rise in intra- vesical pressure. When the bladder's physiological capacity is approached, mechanoreceptors within the detrusor wall are stretched and begin to relay nerve signals to the spinal cord and cerebral cortex to initiate micturition.

Control of detrusor muscle may be disturbed in such a way so as to demonstrate an abnormal pattern of contraction known variously as detrusor hyper-reflexia, detrusor overactivity, uninhibited bladder or bladder instability. Detrusor overactivity is characterized by the occurrence of early, increasingly forceful detrusor contractions that develop well before the bladder reaches physiological capacity limits. If these spontaneous detrusor contractions are of sufficient force, they may overcome the resistance of bladder sphincters and lead to unpredictable urinary incontinence, with the involuntary discharge of small to moderate amounts of urine. Detrusor overactivity is diagnosed by cystometric pressure readings undertaken as part of an urodynamic study. In normal individuals bladder pressure remains low during bladder filling until physiological capacity is approached. In persons with detrusor overactivity, repeated pressure waves occur relatively early in the bladder filling phase and the waves increase in amplitude as bladder volume rises. These pressure waves or spikes correspond to instances of detrusor contraction.

The source of detrusor overactivity is most often unknown in the majority of cases, but there are two broad mechanisms that may induce the disorder:

1) Defective central nervous system sensory input about, and/or control of, bladder function often results in detrusor instability, as may occur in spinal cord transection or injury; congenital disorders such as spina bifida or cerebral palsy, cerebrovascular accidents, demyelinating diseases such as multiple sclerosis, degenerative illness like Parkinson's disease and senile dementia, or diabetic and other autonomic neuropathies .

2) Increased afferent stimulation from the bladder due to an underlying urological condition, for example benign prostatic hypertrophy, urinary tract infection, interstitial cystitis, atrophic urethritis, uterine prolapse or faecal impaction.

In persons whose neurological systems are intact, detrusor overactivity causes frequent, painful sensations of urinary urgency that demand immediate relief. The resulting voluntary or involuntary voiding effectively limits bladder storage capacity. Involuntary voiding as a result of detrusor overactivity is a common and highly problematic condition, known clinically as urge incontinence.

In spinal cord injury or other neurological disorders that impair bladder sensation or control, detrusor over- activity may occur asymptomatically in the setting of defective or complete absence of sensory input to the cortex about filling volume or bladder contractions. The consequence is often non-obstructive urinary retention due to over-filling, together with episodic incontinence. To counter the defects in sensory input and voluntary bladder control, a time-based regime of intermittent voiding via self-catheterization must be followed. In practice, such voiding is frequently either "too early" or "too late" in relation to the actual, intercurrent bladder volume. Progressive bladder hypertrophy, dilatation of the ureters and hydronephrosis are the pathological consequences of the generation of excessively high pressures within the lower urinary tract due to the combination of bladder over-filling with detrusor overactivity. Urine retention further predisposes to recurrent urinary tract infection. The consequent renal damage may eventually lead to chronic kidney failure and premature death.

Strategies for control of bladder function and urge incontinence include behavioural conditioning (not appropriate for patients with spinal or CNS lesions) , medication (oxybutynin, for example), ablation of bladder nerve afferents, surgical remodeling of the bladder, or functional electrical stimulation (FES) of sacral nerve roots to provide continuous inhibition of detrusor contractions (c.f. Medtronic Inc., Minneapolis, Mn. USA "InterStim" device) .

Behavioural strategies have had limited success . Medication is effective in a proportion of cases, but at the frequent cost of systemic side effects due to anti- cholinergic blockade, which may be intolerable to the patient. Bladder nerve de-afferentation is a drastic solution, which is not appropriate in most cases and frequently impairs erectile and bowel function. Surgical remodeling is a radical intervention that aims to improve the bladder storage capacity and counter-act the pathological effects of the condition. It is not a cure. Functional electrical stimulation (FES) may be effective in the control of urinary incontinence, but there are several drawbacks. The stimulation of sacral nerve roots is indiscriminate and may permit excessively high intra-vesical pressure to develop when left in inhibitory mode for excessive periods. Such stimulation may also result in inhibition of reflex bowel emptying or cause involuntary leg lower limb movements. Pain at the implant site (or neuro- stimulator position) and lead migration are two further complications, which necessitate surgical revision in up to 30% of implants. Finally, current FES devices do not at present provide any information to the patient or to control systems about actual bladder volume, instances of detrusor contraction or intra-vesical pressures.

Most recent efforts to remedy these problems and identify bladder filling volume and the occurrence of detrusor contractions have focused on a variety of strategies. These include: • The use of cuff electrodes to record afferent nerve signals originating from mechanoreceptors located in the bladder wall. Analysis of these signals demonstrates two patterns: slow and tonic traffic during bladder filling, with superimposed sharp and sudden spikes of activity related to detrusor contraction. Significant problems of low signal to noise ratio; "cross-talk" recorded from sensory nerve signals originating from sites other than the bladder; and inter-individual variations in sensory nerve functional anatomy remain to be resolved. No such system has yet been applied in clinical practice.

• Direct implantation of electrodes into the detrusor with measurement of electrical impedance changes with muscle activity. This method only provides a relatively crude correlation to bladder volume. However, directly implanted electrodes are liable to erode through the bladder wall, dislodge themselves over time, permit urinary leakage, or provide a focus for infection, as well as inducing fibrosis at the site of implantation. No such system has yet been applied in clinical practice.

• Implanted ultrasound transmitter/receiver arrays . Although possibly effective for volume measurement, this system cannot provide accurate measurements of rapidly changing volume of a bladder, and has not been able to progress to clinical implementation.

• External ultrasound transmitter/receivers are used in diagnosis of bladder disorders, but are bulky and inconvenient when employed for continuous monitoring of bladder volume. Such continuous external ultrasound monitoring cannot detect the onset of bladder contractions .

The absence of a simple, reliable and robust means to measure bladder volume and detect detrusor contractions remains a significant impediment to effective bladder management in neurological diseases and to symptom relief in urge incontinence, amongst other conditions. It is an object of the present invention to overcome or ameliorate problems associated with prior art apparatus in order to better facilitate bladder management in disease states.

SUMMARY OF THE INVENTION

In a preferred aspect of the invention there is an anatomical sensor comprising a transducer having a structure formed by at least one elongate sensor element and attachable against an anatomical part of a human or animal, wherein by linear elongation and contraction the sensor element electrically detects relative changes in dimension or configuration of the anatomical part; and a measurement circuit connected to the transducer captures electric signals from the transducer for processing.

In another preferred aspect of the invention there is a method of detecting volume changes of a mammalian bladder using the anatomical sensor defined in any one of the preceding claims including: filling a bladder with fluid; as the bladder is being filled, calibrating the volume of the bladder against an electric signal from the transducer; recording volume measurements against electric signals; and using the recorded data measurements to consequently monitor real or apparent volume changes of the bladder by capturing electric signals generated by the sensor.

In yet another preferred aspect of the invention there is a sensor for distinguishing and monitoring real or apparent volume changes in a mammalian bladder comprising a transducer having a structure formed by at least one elongate sensor element and attachable around at least part of a bladder so as to linearly elongate or contract with changes in dimension or configuration of the bladder, wherein by elongation or contraction the sensor element electrically detects relative changes in dimension or configuration of the bladder; and a measurement circuit connected to the transducer captures electric signals from the transducer for processing.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is described further by way of example with reference to the accompanying drawings of which:

Figure 1 is a perspective view of an embodiment of an anatomical sensor of the invention;

Figure 2 is a first side view of the anatomical sensor;

Figure 3 is a second side view of the anatomical sensor; Figure 4 is a plan view of the anatomical sensor;

Figure 5a is cross-sectional view along the length of a sensor element in a contracted position;

Figure 5b is a cross-sectional view similar to Figure 5a but showing the sensor element is an expanded position;

Figure 6 is a block diagram of the electric circuit of the sensor;

Figure 7 is a chart showing the results of readings taken from a sensor implanted on the bladder of a sheep; and

Figure 8 is a chart showing the results of electrical stimulations of a sheep's bladder.

DETAILED DESCRIPTION OF THE INVENTION

The present anatomical sensor is in the form of a sensor transducer device that accurately measures changes in a linear dimension such that, by the operations of geometry as these apply to a sphere, cone, cylinder or other geometric form, the dynamic dimensions, volume, angular displacement or contractile activity of an internal bodily organ, or any external anatomically defined body section or limb, or part thereof, may be continuously derived.

In its particular embodiment, the anatomical sensor consists of a surgically implanted electro-mechanical transducer assembly comprising one or more sensor elements adapted so as to provide highly accurate, real-time measurement and recording of the filling volume of a mammalian bladder on a continuous or intermittent basis.

The transducer assembly is also preferably adapted to detect the onset and quantify the strength and duration of contractions of the detrusor muscle during bladder filling over a wide range of volumes .

In order to indirectly stimulate or inhibit certain bladder functions the assembly may optionally include microprocessor-controlled electrical signal generator circuits that produce voltage or current controlled waveforms with variable frequency and duty cycle, connected via electrical wire or wireless communication to electrodes placed around peripheral efferent nerves (or adjacent to the bladder neck wherein nerve fibres pass) that carry nerve signals controlling or modulating detrusor muscle or bladder sphincter function.

The anatomical sensor 10 illustrated in the drawings has one or more discrete electro-mechanical sensor elements 11 constructed of elastic, and electrically conductive materials that together comprise a transducer assembly in the form of an open net or cage. The sensor 10 is adapted for surgical attachment to the bladder neck, wherein the transducer assembly faithfully conforms to the spherical surface of the organ. It is adapted to detect, measure, modify, store, and transmit variations in particular electrical properties during elongation or contraction of individual sensor elements in tandem with changes in circumference of the bladder attributable to real or apparent alterations in bladder volume. Where only a low number of sensor elements 11 are used and the amount is insufficient to form a fully ramified open mesh around the bladder, the elements 11 may be interconnected to a base 12 in the form of a open mesh made up from additional, interconnected, non-sensing elastic members that envelops the bladder as illustrated in Figure 1. Base 12 ensures the sensor elements 11 conform faithfully to the surface of the bladder to accurately detect any changes in dimensions and shape.

Figures 5a and 5b illustrate one preferred embodiment of the sensor elements 11 comprising the transducer assembly. In this embodiment each sensor element contains a pair of concentrically wound helically coiled conductive wires 15 held within a silicone elastomer sheath 16 or coating. The ends 17 of the wires are left open so as to form an open circuit within which capacitance changes occur as one wire moves relative to the other during elongation or contraction of the sensor. Figure 5a illustrates the sensor element 11 in a contracted position, whereas Figure 5b illustrates the element 11 in an elongated position. The sensors are thereby adapted to measure capacitance changes in response to changes in the length of a particular chord of the bladder wall circumference.

One such electronic sensor element is called an extensometer and is described in U.S Patent 5,090,248. The extensometer described therein is a highly sensitive indicator of longitudinal deformation, whether small or large. The inherent flexibility and elasticity of the extensometer provides for arcuate conformability such that length determination is very accurate over any variably changing curved surface to which it conforms . In the present application, the transducer assembly comprises one or more extensometers each embedded in a suitable medical-grade elastic dielectric material, and formed into an assembly, together with integrated circuits. The integrated circuits are capable of detection and measurement of capacitance changes in the sensor element, conversion and amplification of these capacitance changes into a varying DC voltage signal, and further conversion of analogue voltage signals to digital signals that are then subject to microprocessor analysis to derive changes in volume and contraction events, for the control of nerve actuator electrodes and patient notification.

Other configurations of sensor elements are also available. For example, the two helically coiled conductive wires contained within an elastic polymer sheath or coating as described above can be joined in continuity at one end to form a closed circuit such that this closed circuit demonstrates measurable changes in electrical inductance in proportion to lengthening and shortening of the sensor around a curved surface. Hence the integrated circuit in this embodiment measures inductance.

In another embodiment a single coiled conductive metal wire is contained within an elastic polymer sheath or coating. This wire demonstrates measurable changes in electrical inductance during elongation or contraction around a curved surface

Alternatively, the transducer sensor element may comprise a linear sensor made of an elastic, conductive material e.g. a conductive polymer, which demonstrates measurable changes in electrical resistance during elongation or contraction around a curved surface.

Taking this concept further the sensor element may instead comprise two discrete linear sensors aligned in parallel as an open circuit and which demonstrate measurable changes in electrical capacitance between each other, in proportion to change in effective plate area and separation gap of the conductive polymer, during elongation or contraction around a curved surface. On the other hand, joining the linear sensors end to end in continuity to form a closed circuit provides a construction that demonstrates measurable changes in electrical impedance during elongation or contraction around a curved surface.

While in its present embodiment the anatomical sensor takes the form of a mesh transducer for wrapping around a bladder to distinguish and monitor the real or apparent volume changes in a bladder, the concept can be equally applied to monitor other internal organs or external body parts . In these other cases the shape and configuration of the anatomical sensor would be made to suit the particular anatomical part to which it is intended to be attached. The anatomical sensor usefully provides accurate information regarding the activity of the particular body part to which it is attached so that the body part may be monitored and/or action implemented in response to information obtained by the sensor .

In the preferred embodiment the sensor element 11 comprises two lengths of fine and pliable electrically conductive wires wound in a single interposed double helix coil configuration such that the cross-sectional profile of the paired conductors forms an oval or circular shape. The sprung coils are completely immersed and ensheathed in a dielectric elastic material with a high index of elasticity. Suitable elastic dielectric materials include medical-grade silicone rubbers or elastomers.

As shown in Figures 1 to 4, three or more sensor elements are attached to one another to form a spherical or hemi-spherical "cage" conforming to the bladder wall. Anchoring arms of anchor 13 attach the cage to the bladder neck and, together with a transducer microprocessor 22, make up the transducer assembly of the device.

The conductive wire pairs are connected to the measurement circuit at one end of each sensor element and are open at the other end. Figure 6 schematically illustrates the components of the circuitry of the sensor. A capacitance measurement circuit 20 is attached to the insulated wires 11 to capture the capacitance values of the helically wound conductive pair as these alter in line with changes in the pitch of the coils and subsequent separation of the coils relative to one another during longitudinal distraction of the sensor. The output of the capacitance circuit takes the form of analogue voltage fluctuations that are then converted to digital signals via analogue-to- digital integrated circuit 21. The further processing of these digital signals by the controller circuit may take place partly in the transducer assembly electronics (microcontroller 22) or entirely in the external receiving device, once transmitted via wireless transmission by transceivers 24 to an externally located microprocessor controller 23 and display circuits 25. The anchor 13 of the transducer assembly is anchored to the bladder neck during surgery and the "cage" of the transducer assembly conforms closely to the bladder's spherical shape once a nominated or starting volume has been attained, in practice 0-100 milliliters. Beyond the nominated starting volume, any distraction or retraction of the paired wire conductors within the sensor elements during, respectively, expansion or contraction of the external bladder wall associated with true volume shifts, or the apparent minor volume changes of a non-voiding detrusor contraction, will result in a parallel modification in their electrical interaction, and in particular the degree of capacitance that exists between the conductive pair.

Capacitance between the conductive wire pair is inversely related to the sensor elongation up to a predetermined multiple of its original length. When capacitance changes arising from distraction of the transducer assembly are plotted against the known starting circumferential length of the extensometer (that corresponds to a known starting bladder spherical volume) , changes in the bladder wall chord length and - by geometry - the bladder volume itself can be derived and quantified within the controller circuit.

In the following, the operation of the sensor will be discussed in terms of the embodiment of the sensor element described above having a pair of helically coiled open conductors ensheathed in an elastic material . The alternate embodiments of the sensor referred to previously would operate in a similar manner.

During bladder filling, volumetric expansion inflates the dome of the bladder. This expansion of the curved surface of the external bladder wall induces changes to the state of capacitance existing between the paired helical conductors of the sensor elements embedded within the transducer assembly as it lengthens in tandem with the bladder wall to which it conforms.

The anatomical sensor is calibrated to every individual in whom the sensor is implanted. By means of calibration of the capacitance changes that occur with instillation of defined volumes of fluid via urethral catheter as part of the implantation procedure, accurate filling volumes on an on-going basis are titrated for every single individual in whom the transducer assembly is implanted. Further periodic calibration and verification may be carried out post implant via catheterization with the use of wireless transducer analysis equipment .

Data points obtained from the controlled titration of fluid volumes into the bladder via an urinary catheter during the implantation procedure permit exact calibration of sensor parameters in the controller circuit so as to encompass the unique anatomy, filling geometry and capacity of the recipient's bladder. This allows dynamic variations in bladder volume to be accurately quantified based on changes to the external bladder wall circumferential length.

The information obtained from repeated or continuous monitoring will, once processed, accurately measure actual bladder filling volume.

Restoration of the transducer assembly following deflation of the bladder as a result of micturition is achieved by both the inherent recoil properties of the conductors and the elastic material in which they are embedded.

One further advantage of the transducer is that mechanical distraction of the conductor wires directly parallels mechanical expansion of the bladder wall itself. Bladder filling expands the bladder on a continuous basis and this, in turn, is faithfully reflected by the continuous uni-directional changes in capacitance values between the helical conductors in the sensors of the implanted transducer assembly.

The onset and progress of any mechanical contraction of the detrusor muscle within the bladder wall (whether associated with voiding or not) necessarily results in the arrest and reversal of the previous pattern of mechanical elongation of the conductor wires, an event that can be identified by detecting reversal of the immediately preceding direction of capacitance change in the conductor wires of the sensors. The transducer can thereby sense each and every detrusor contraction at a very early phase of evolution.

In addition, the rate of change and extent of this reversal allows determination of the developing speed and force of the detrusor contraction, and can be further correlated with the amplitude of intra-vesical pressure spikes captured by cystometric pressure readings taken from those who have the sensor implanted.

Whereas detrusor contractions are capable of being identified in this manner, the further evolution of an unwanted detrusor contraction can be thwarted by inhibitory nerve stimulation of appropriate efferent nerves to the bladder wall on an automatic, event-driven basis via the appropriate modulation of efferent nerve signals transmitted to the bladder by peripheral nerves.

Normal patient activities can induce lateral movements or compression of the bladder to the effect that that shape of the bladder is passively distorted for a temporary period. Such distortions risk generating volume or contraction artifacts in the implanted transducer assembly.

The sensor elements in the transducer assembly can be configured in opposing pairs. Each vertically aligned sensor element 11a has a vertically aligned pair on an opposing side of the sensor cage. A single circular horizontal element lib is illustrated in Figure 1. This sensor element is an opposed pair to any of the vertical sensor elements 11a by virtue of their orthogonal relationship. An advantage of the disposition of sensor elements in this configuration is that they collectively function as a stress/strain gauge. This is because some elements are horizontally aligned whilst others are vertically aligned. Therefore during lateral bladder movements capacitance readings from an individual sensor in the vertical plane will always move in a contrary direction to its opposite vertical member, whilst both will move contrary to a horizontal sensor during bladder compression.

Distortions of bladder shape cause opposing changes in capacitance as recorded from variously aligned sensors and when summated these capacitance changes are, in effect, self-canceling. This property assists in blocking the appearance of volume or contraction artifacts. Once individual bladder volume changes are properly calibrated with the implanted transducer assembly, continuous or intermittent readings of true bladder volume and instances of detrusor contraction are available at all times through the external controller circuit. Detrusor contractions can be disclosed to a recipient by means of digital read-out 25, LED, auditory alarms or warnings, vibration alert 26 (Figure 6) , wireless radio transmission or any other method of communication. Alternatively the digital signals indicating detrusor contractions can be further processed to provide input to automated electrical nerve stimulation control devices that interrupt the further evolution of the contraction event, or permit micturition.

Satisfactory operation of the present invention has been demonstrated by a series of experiments with sheep during which the transducer assembly was attached to the bladder and volume and pressures recordings made overnight. Experimental electrical induction of bladder contractions confirmed the capability of the transducer assembly to detect bladder contractions .

Figure 7 illustrates chart readings from an anatomical sensor implanted on the bladder of a sheep. The sensor was implanted according to normal surgical procedures. The cage of the sensor was slipped over the dome of the bladder and anchored by ties, stitches or other methods of connection at the neck of the bladder, accommodating the lateral ligaments where necessary.

The chart of Figure 7 illustrates readings from four sensor elements, namely 1A, 2A, 3A and 3B. The chart also illustrates pressure reading P taken from a catheter inserted into the sheep bladder through the urethra. The catheter was connected to data recording equipment to monitor the bladder pressure.

The chart records sensor element extension and pressure in terms of millimeters versus time. The readings were taken at a time when the sheep was recovering from surgery and had been placed overnight in a recovery pen where the sensor data could be logged throughout its natural urination cycles.

The chart illustrates that the sensor elements were able to pick up the gradual increase in bladder volume over time as the bladder filled, which appears as a steady rise in extension of the sensor elements. Pressure remained relatively constant during the fill . Immediate drops in the length of the sensor elements demonstrate the points at which urination occurred. Sensor elements 1A and 3A were located across the crown of the bladder and lower anterior bladder wall respectively and showed the greatest sensitivity in detecting the changing volumes of the bladder.

Figure 8 is a chart showing the readings taken from two sensors, 1A and 3A, and a pressure sensor P when the bladder was electrically stimulated to artificially induce bladder contractions. Parallel electrodes were placed around the base of the bladder and pulses of current were sent through the electrodes. In the test a 40 Hz bipolar square wave signal was injected into the electrodes to artificially stimulate the detrusor muscle against a closed urinary sphincter. The Figure 8 graph illustrates two principles:

Firstly, during the repetitive stimulation of detrusor contractions, sensor elements 1A and 3A produced tracings that always moved in opposite directions to each other; 1A moved downwards, and 3A moved upwards. 1A was located over the posterior crown of the bladder dome and 3A over the lower anterior bladder wall. Since detrusor contractions commence in the crown and move downwards over the bladder this demonstrated that 1A contracted in length whilst 3A elongated with each contraction. This in turn indicates that volume was reduced by contraction at the crown whilst it increased below as the bladder bulged outwards against the closed sphincter.

These results prove that the sensor, in this case 1A, can detect a bladder contraction. Once contractions are detected steps may be taken to inhibit the contractions by electrically stimulating appropriate efferent nerves in the bladder walls.

Secondly, and unrelated to the sensor function, repetitive detrusor contractions provoked by efferent nerve stimulation show diminished strength with each subsequent stimulation in the train. This is illustrated in the progressively smaller peaks or troughs in the second stimulation sequence.

Since persons skilled in the art may readily effect modifications within the spirit and scope of the invention, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, hereinabove .

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An anatomical sensor comprising a transducer having a structure formed by at least one elongate sensor element and attachable against an anatomical part of a human or animal, wherein by linear elongation and contraction the sensor element electrically detects relative changes in dimension or configuration of the anatomical part; and a measurement circuit connected to the transducer captures electric signals from the transducer for processing.

2. The sensor claimed in claim 1 wherein the sensor element comprises two coiled conductive wires contained in an elastic sheath.

3. The sensor claimed in claim 2 wherein the wires are interposed and helically wound.

4. The sensor claimed in claims 2 or 3 wherein the wires are aligned in parallel to form an open circuit.

5. The sensor claimed in claim 4 wherein by elongation or contraction of the sensor element the measurement circuit captures electrical changes in capacitance in the sensor element.

6. The sensor claimed in claims 2 or 3 wherein the wires are aligned in series to form a closed circuit.

7. The sensor claimed in claim 6 wherein by elongation or contraction of the sensor element the measurement circuit captures electrical changes in inductance of the sensor elements .

8. The sensor claimed in claim 1 wherein the sensor element comprises a single coiled conductive wire contained in an elastic sheath.

9. The sensor claimed in claim 8 wherein by elongation or contraction of the sensor element, the measurement circuit captures electrical changes in inductance of the sensor element.

10. The sensor claimed in claim 1 wherein the sensor element is an elongate member made of a conductive elastic material and by elongation or contraction of the sensor element the measurement circuit captures electrical changes in resistance in the sensor element.

11. The sensor claimed in claim 1 wherein the sensor element comprises two elongate members made of a conductive elastic material.

12. The sensor claimed in claim 11 wherein the elongate members are aligned in parallel to form an open circuit and by elongation or contraction of the sensor element the measurement circuit captures electrical changes in capacitance in the sensor element.

13. The sensor claimed in claim 11 wherein the elongate members are aligned in series to form closed circuit and by elongation or contraction of the sensor element the measurement circuit captures electrical changes in impedance in the sensor element.

14. The sensor claimed in claim 1 wherein multiple sensor elements within the transducer are configured in opposing pairs such that passive distortion of the bladder shape results in self-canceling changes in capacitance or other electrical properties between opposing sensor elements to exclude recording artifacts.

15. The sensor claimed in claim 14 wherein the transducer is configured such that a sensor element oriented in one direction has an opposing sensor element pair oriented in the same direction.

16. The sensor claimed in claim 14 wherein the transducer is configured such that a sensor element oriented in one direction has an opposing sensor element pair oriented in a substantially orthogonal direction.

17. The sensor claimed in any one of the preceding claims wherein two or more sensor elements are attached together to form a flexible lattice capable of surrounding and attaching to an anatomical part .

18. The sensor claimed in any one of claims 1 to 16 wherein one or more sensor elements may be enmeshed with a flexible elastic base that is capable of surrounding and attaching to an anatomical part .

19. The sensor claimed in any one of the preceding claims further comprising an analog-to-digital integrated circuit that converts analog signals from the measurement circuit to digital signals.

20. The sensor claimed in claim 19 wherein a transmitter connected to the transducer wirelessly transmits the digital signal to a remote microprocessor.

21. The sensor claimed in claim 20 wherein a microcontroller unit connected to the transducer conditions and processes the digital signal before transmitting to the remote microprocessor.

22. The sensor claimed in any one of the preceding claims wherein alarms or other alerting means alert a user that the transducer has reached a pre-defined measurement value.

23. The sensor claimed in claim 22 wherein alarms or other alerting means include auditory or visual alarms, vibration of a hand-held receiver or a digital read-out.

24. The sensor claimed in any one of the preceding claims wherein the sensor is used for monitoring the volume of a mammalian bladder.

25. The sensor claimed in claim 24 wherein the transducer has an anchor to fix the anatomical sensor to the neck of the bladder.

26. The sensor claimed in claim 24 wherein the sensor detects and quantifies detrusor contractions in the bladder by monitoring fluctuations in the extension of the sensor element .

27. The sensor claimed in claim 26 further comprising an actuator to perform an action in response to information from the electric signal generated by the transducer.

28. The sensor claimed in claim 27 wherein the actuator stimulates or inhibits detrusor contractions in response to fluctuations in the extension of sensor element.

29. The sensor claimed in claim 28 wherein the actuator comprises at least one electrode to stimulate or inhibit efferent nerves to the bladder and thereby induce or inhibit detrusor contractions.

30. The sensor claimed in claim 27 wherein the actuator enables voluntary initiation of voiding of a bladder once the transducer detects the bladder reaching a predetermined electric signal representing a predetermined bladder volume.

31. A method of detecting volume changes of a mammalian bladder using the anatomical sensor defined in any one of the preceding claims including: filling a bladder with fluid; as the bladder is being filled, calibrating the volume of the bladder against an electric signal from the transducer; recording volume measurements against electric signals; and using the recorded data measurements to consequently monitor real or apparent volume changes of the bladder by capturing electric signals generated by the sensor.

32. The method claimed in claim 31 whereby bladder volume is measured in terms of the capacitance, inductance, impedance, resistance or stress/strain properties of conductive materials.

33. The method claimed in claim 31 including titrating the fluid before filling the bladder so as to obtain accurate measurements of bladder volume.

34. The method claimed in any one of claims 31 to 33 whereby nerves in proximity to the bladder are electrically stimulated in response to predetermined electrical signals generated by the sensor so as to inhibit detrusor contractions or encourage micturition.

35. A sensor for distinguishing and monitoring real or apparent volume changes in a mammalian bladder comprising a transducer having a structure formed by at least one elongate sensor element and attachable around at least part of a bladder so as to linearly elongate or contract with changes in dimension or configuration of the bladder, wherein by elongation or contraction the sensor element electrically detects relative changes in dimension or configuration of the bladder; and a measurement circuit connected to the transducer captures electric signals from the transducer for processing.