Urodynamics studies require the measurement of bladder pressure and urine flow during voiding of the bladder. For the past thirty years or so, bladder pressure measurements have been made using catheters that are placed, via the urethra, into the bladder. There are two basic methods.

In the first method, the distal end of a catheter is introduced into the bladder, with the proximal end remaining external to the body. The catheter thereby provides fluid communication from the bladder to the outside of the body. The catheter facilitates filling of the bladder and, by the fluid column contained within the catheter, provides pressure communication to a pressure sensor at the proximal end of the catheter, external to the body. Typically, pressure measurements are required both during filling and voiding of the bladder, in which case a multiple lumen catheter is used, with at least a first lumen providing the bladder filling capability and at least a second lumen providing pressure communication to the external pressure sensor. Voiding takes place past the catheter through the urethra.

In the second method, one or more strain gauges are coupled to the distal end of the catheter, which strain gauges are electrically connected to an external recording device by way of wires incorporated into the catheter. A typical pressure transducer comprises a metal sensing diaphragm mounted within a soft flexible silicone rubber portion of the catheter and resistive strain gauge.

The lumen of the catheter provides the filling capability.

As the bladder is situated within the peritoneum, it is also desirable to record peritoneal (abdominal) pressure, which is then subtracted from the bladder pressure readings in order to establish true bladder pressures.

In a clinical study, the bladder is filled with fluid using the catheter and a peristaltic pump. When the patient feels that the bladder is full, voiding takes place, past the catheter, into a flow meter. The flow meter is connected electronically to the same recording device as the pressure sensor so that a chart can be produced logging bladder pressure, abdominal pressure, true bladder pressure and flow against time.

Because of the complexity of the apparatus, normally the patient must be connected to the measuring equipment and remain relatively immobile for the duration of the study. The requirement for artificial filling, using a catheter, results in more discomfort for the patient, limited ambulatory capability, and a restriction on flow during voiding which compromises the measurements being taken, at least in part due to the diameter of catheter required to provide bladder filling.

For example, in one existing multiple lumen system, the filling lumen occupies twice as much cross-sectional area of the catheter than does each of the two pressure sensing lumens.

Accordingly, it is an object of the invention to provide a fully portable measurement system that enables full mobility of the patient, during a period of time that is commensurate with natural filling of the bladder.

It is a further object of the invention to provide a bladder pressure sensing system that enables voiding to take place without the urethral restriction resulting from a filling catheter.

It is a further object of the invention to provide a urodynamics measurement system that integrates the pressure sensing data collection and the flow sensing data collection into a single, fully portable unit that can be readily carried or worn by the patient.

According to one aspect, the present invention provides a remote pressure transducer capsule adapted for introduction into the human bladder via the urethra comprising: a capsule housing; a pressure transducer; and a retrieval and communication lead extending from the housing for passage through the human urethra.

According to another aspect, the present invention provides a portable urodynamics measurement system comprising a pressure transducer as defined above together with a data recording device, coupled to the pressure transducer by way of the retrieval and communication lead, for recording measurements from said pressure transducer as a function of time.

According to another aspect, the present invention provides a remote pressure transducer capsule adapted for introduction into the human bladder via the urethra comprising: a capsule housing; a pressure transducer; a wireless telecommunication device for communicating pressure data to a remote receiver; and a retrieval lead extending from the housing suitable for passage through the human urethra to withdraw the capsule therethrough.

According to another aspect, the present invention provides a method of making urodynamics measurements on a patient's body comprising the steps of : inserting a pressure transducer capsule into the bladder via the urethra, leaving a retrieval and electrical communication lead extending from the pressure transducer to a position external of the body; connecting said communication lead to a portable data recording device carried by the patient; and automatically monitoring and recording pressure signals from the pressure transducer, by the data recording device.

Embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a urodynamics measurement system according to the present invention; and Figure 2 is a perspective view of a remote pressure transducer according to the present invention in (a) unencapsulated form, and (b) encapsulated form.

With reference to figure 2 (a), a pressure sensor 10 comprises a pressure sensing die 11 mounted on a substrate 12, via an interface circuit 13 preferably formed as an application specific integrated circuit. The interface circuit may provide control electronics for the pressure transducer, and/or a data transfer interface.

The interface circuit 13 is connected to a lead 14 which provides electrical communication to a data recorder remote from the pressure sensor 10, and also provides a mechanical means for withdrawing the sensor from an installed position within the bladder.

With reference to figure 2 (b), the pressure sensor 10 is encapsulated in a housing of suitable material having a window membrane 15 allowing pressure communication to the pressure sensing die 11. The encapsulation material thus completes formation of a pressure sensor capsule 10 protecting the sensing die

11 and interface circuit 13 from ingress of harmful fluids. The capsule 10 is also preferably shaped and sized to allow easy introduction of the capsule into the human bladder, via the urethra.

In a typical preferred embodiment, the capsule is approximately 15 mm long, of approximately circular cross-section 4 mm in diameter, being generally suitable for introduction to the bladder by way of the urethra. The housing material is preferably silicone or polyurethane.

Preferably, the capsule is constructed of suitable materials such that its specific density is less than that of water, and particularly that of urine, so that the capsule floats within the bladder. In one embodiment, the capsule density is less than 1 g/cm3.

The pressure sensor capsule 10 is preferably provided with a flexible installation device (not shown) to enable the capsule to be driven into the bladder via the urethra, the installation device then being withdrawn leaving the capsule 10 within the bladder and the lead 14 extending through the urethra to a point external to the body. The installation device is preferably similar to a drinking straw or catheter, through which the lead 14 passes. After positioning the capsule 10 in the bladder, the capsule is released from the distal end of the catheter and the catheter is withdrawn over the lead 14 until completely detached at the proximal (external) end of the lead 14.

With reference to figure 1, the pressure sensor capsule 10 is installed into the bladder 20 and the lead 14 connected to a portable data recording device 30.

In the preferred embodiments, the portable data recording device 30 is similar in size to a mobile telephone, and houses a power source (not shown) for. providing power to both the data recording device 30 and the remote pressure sensor capsule 10. The data recording device also includes a memory 31 for

storing data received, and program instructions for the operation of the device; a microprocessor 32 for handling the data processing activity; and an analogue to digital converter (ADC) 33 for pre-processing analogue pressure signals received from the pressure sensor capsule 10. It will be understood that some of the functions (in particular those of the ADC) could be remotely located in the remote pressure sensor capsule 10.

The data recording device 30 also preferably includes a wireless telecommunications transmitter and/or receiver 34 for receiving signals from a flow meter unit 40 which will typically be installed in a cubicle or room affording privacy to the patient, within the hospital or clinic. Flow meters are well known in the art and generally provide a collection vessel for receiving urine during voiding, coupled to a weighing scale that reads the mass of urine collected as a function of time, thereby providing a volume and flow rate determination.

Data from this volume and flow rate determination are furnished to the portable data recording device 30 by way of a transmitter 41 within the flow meter unit 40 which communicates with the receiver 34.

The urodynamics measurement system preferably also includes a data processing device, eg. PC 50, for receiving data collected by the portable data recording device 30, enabling analysis and display of the collected data.

Communication with the data processing device 50 may be by wireless telecommunications link or by plug in connection once the patient has removed the portable device 30.

In use, a clinician installs the remote pressure sensor capsule 10 into the patient's bladder, using a suitable installation device. The proximal end of the communication lead 14 is then coupled to the portable data recording device 30 which the patient carries, for example strapped to a leg or in a pocket. After a

suitable period of natural bladder filling, the patient visits the flow meter unit 40 to empty the bladder, at which time the flow rate measurements are made and transmitted to the data recording device 30.

Preferably, a communications protocol is established between the flow meter unit 40 and the data recording device 30 so that the identities of each device are used during data transfer to ensure that data is collected and transferred for the correct patient, in a system having multiple data recording devices in use at any one time.

The use of only a thin electrical communication wire 14, rather than the large diameter (> 2-3 mm) fluid pressure sensing catheters of the prior art means is beneficial for a number of reasons.

Firstly, the connection of the capsule 10 to the data recording device 30 is easily configured and routed eg. around clothing, so that the patient is able to move around relatively normally during the data collection period. The filling of the bladder can therefore be conducted naturally over a period of time rather than forced filling using a catheter and peristaltic pump.

Secondly, during voiding of the bladder, the thin electrical communication lead 14 offers much less resistance to flow of urine through the urethra therefore providing more accurate measurements.

Further, the patient need not be connected up to a conventional urodynamics machine during the duration of the measurements, therefore throughput of patients in the clinic can be much higher than a typical figure of one per hour with some existing systems. The risk of spillage from pressure sensing catheters emerging from the body is eliminated. The patient experiences less discomfort during the measurements.

It is found that the accuracy of measurements from the remote pressure sensing capsules is also increased and the data capture can conveniently be made more comprehensive. In addition, once the pressure sensor capsule has been installed in the patient, the procedure requires no further clinical expertise or intervention to capture the required data.

After completion of the data collection, the pressure sensor capsule 10 can be removed from the bladder simply by pulling on the communication and retrieval lead 14.

For more accurate clinical measurements, it is preferred to monitor both bladder pressure and abdominal pressure. This is easily achieved using the apparatus as described above by providing a second remote pressure sensor capsule 10 installed via the rectum. The second remote pressure sensor capsule may be of the same type as the one used in the bladder, or may be of a different type. Abdominal pressure measurements are thus communicated contemporaneously with the bladder pressure measurements to the data recording device 30 where they can be stored and analysed later. In the preferred embodiments, abdominal pressure measurements are subtracted from the bladder pressure measurements to provide true bladder pressure. It will be understood that this could be done in real time by the data recording device 30, or during data analysis, eg by the data processing device 50.

In a still further embodiment of the invention, the lead 14 may provide only a mechanical function for retrieval of the remote pressure sensor capsule 10. In this embodiment, the pressure transducer may be provided with a transponder for wirelessly communicating pressure measurements to the data recording device 30.

The pressure sensor capsules of the present invention can be manufactured at very low cost using well known integrated circuit fabrication techniques. This

makes the capsule-based pressure sensor a low cost, disposable item offering considerable savings over various catheter-based system which are either disposable at relatively high cost, or must be thoroughly cleaned and sterilised (eg. using detergicides, ethylene oxide gas, or sodium hypochlorite solutions.

The cleaning and sterilising operations greatly increase the cost of the systems and increase risks of infection.

Other embodiments that will be apparent to those skilled in the art are within the scope of the accompanying claims.