WO2009055866A1

WO2009055866A1 - Implantable medical prothesis system capable of detecting symptoms of medical conditions

Info

Publication number: WO2009055866A1
Application number: PCT/AU2008/001620
Authority: WO
Inventors: John Chambers
Original assignee: Cochlear Limited
Priority date: 2007-10-31
Filing date: 2008-10-31
Publication date: 2009-05-07

Abstract

A medical prosthesis system is provided. The system includes an implantable component (100) configured to be implanted in a patient and apply stimulation to the patient based upon processed stimulation signals produced from a processor (203, 208). One or more detectors are arranged to detect one or more physiological parameters of the patient and produce physiological parameter signals representative of the detected parameters. The processor (203, 208) is configured to receive the physiological parameter signals and perform an analysis operation to determine whether the detected parameters meet predetermined conditions representative of a specific physiological condition. If the predetermined conditions are determined to have been met, the system provides an alarm or other indication that a specific physiological condition has been detected.

Description

IMPLANTABLE MEDICAL PROTHESIS SYSTEM CAPABLE OF DETECTING

SYMPTOMS OF MEDICAL CONDITIONS FIELD OF THE INVENTION

The present invention relates to implantable medical devices which apply stimulation to a patient.

BACKGROUND TO THE INVENTION

A wide variety of implantable medical devices are used for applying stimulation to internal body parts of patients. As an example, hearing prostheses, such as cochlear implants, are used to assist people with total or partial hearing loss. In general, such devices transform received sound signals into electrical stimulation signals. By applying these electrical stimulation signals to the neural hearing system of a person, the person is able to perceive an approximation of sound.

A typical cochlear implant system includes one or more sound transducers such as microphones, for converting received sound signals into electrical audio signals. In the case of the sound transducer producing analogue electrical audio signals, these signals are converted to a digital representation by an analogue-to- digital converter to allow the audio signals to be processed as electronic data. The digital audio signals undergo complex signal processing to optimise the signal for the purposes of conversion to electrical stimulation signals. The electrical stimulation signals are then provided to a neural stimulator which in turn applies electrical stimuli to the neural hearing system of the recipient.

The implantation procedure, like any invasive operation, poses issues of post-operation risk of infection at the site of the surgery or complications with body rejection of the implanted component. Such risk is at its greatest during the first few weeks after implantation. The onset of such problems is often not readily detectable by medical practitioners until physical symptoms become apparent, by which time urgent remedial treatment is required. While an adult implantee may be able to communicate that they feel the onset of possible symptoms, an infant or other person with communication difficulties is not able to convey precisely what they are feeling. SUMMARY OF THE INVENTION

In a broad form, the present invention relates to an enhanced medical prosthesis system capable of detecting selected physiological parameters of the patient and providing an indication of an alarm condition in the event that the parameters individually or in combination exceed predefined limits.

According to the present invention there is provided a medical prosthesis system, including: an implantable component configured to be implanted in a patient and apply stimulation in any form, be it electrical, mechanical or other, to the patient based upon processed stimulation signals; a processor for producing the processed stimulation signals; and one or more detectors for detecting one or more physiological parameters of the patient and producing physiological parameter signals representative of the detected parameters; wherein the processor is configured to receive the physiological parameter signals and perform an analysis operation to determine whether the detected parameters meet predetermined conditions representative of a specific physiological condition, wherein if the predetermined conditions are determined to have been met the system provides an alarm or other indication that a specific physiological condition has been detected.

According to preferred embodiments of the invention, suitable detectors include:

• a temperature sensor incorporated in the implantable component for sensing body temperature of the patient; • a microphone for detecting sounds of the patient breathing or vocalizing;

• a pressure sensor incorporated in the implantable component for detecting the pulse of the patient;

• electrodes incorporated in the implantable component which can be configured to detect electrical impedance of body tissue and/or voltages generated by neural and/or muscular activity;

• a biological antigen senor incorporated in the implantable component; • a blood sugar concentration sensor incorporated in the implantable component; and

• an accelerometer incorporated in the implantable component for detecting accelerated body movement of the patient. In exemplary embodiments, the system further includes a memory for storing said physiological parameter signals. This allows the processor to refer to stored physiological parameter signals when performing the analysis operation on current physiological parameter signals.

Preferably, the system further includes an alarm unit for receiving the indication and providing a perceivable alarm.

The present invention advantageously provides a medical prosthesis system which can detect and indicate the potential onset, presence or change of a medical condition in the patient.

It is relevant to note that public health websites offering information about meningococcal disease in babies and infants describe the following symptomatic conditions:

• Fever;

• Grunting, Moaning or high-pitched cry;

• Blank, staring expression; • Inactive, drowsy, floppy or lethargic or irritable;

• Convulsions or twitching.

Preferred embodiments of the present invention advantageously monitor changes in physiological parameters which are attributable to such conditions. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a functional block system diagram of a preferred embodiment of an implantable component of a hearing prosthesis system; and

Fig. 2 is a functional block diagram of a preferred embodiment of an external processing component in communication with the implantable component of Fig. 1. DESCRIPTION OF PREFERRED EMBODIMENTS

The following description illustrates a preferred embodiment of the invention as applied to a hearing neural stimulation system. It will be appreciated that the invention could be implemented in a variety of ways and can find application in other forms of medical prosthesis systems.

Figs. 1 and 2 illustrate the main functional blocks of a hearing prosthesis system according to an embodiment of the present invention. The system illustrated has an implant component 100 and a non-implanted external component 200 which houses the main processing capabilities of the system. It will be appreciated that the present invention could be adapted for use in a total implant system, in which case the main processing capabilities would be incorporated into the implant component 100.

Referring to Fig. 2, the external component 200 includes a sound transducer 201 which is preferably one or more microphones, telecoil induction pickup coils or other electrical signal sources representing sound.

The output of the sound transducer is an analogue electrical audio signal. As illustrated, a number of processing steps are performed to the incoming analogue electrical audio signal.

Initially, the conditioner and A/D converter block 202 conditions the analogue electrical audio signal and converts it into a digital signal.

The sound data processing block 203 then applies complex digital signal processing to the digital audio signal. It will be appreciated by those skilled in the art that digital signal processing techniques presently employed in known hearing prosthesis systems can be used here. The processed audio signal is encoded into a stimulation signal suitable for delivery to a stimuli transducer, such as the electrodes of the implanted component 100. Typically, during the processing stage, user-specific parameters are applied to the signal, to customise the electrical stimulation signals in accordance with the recipient's requirements. These customising parameters are normally determined in consultation with a clinician during a clinical 'mapping' procedure and are programmed into the system via a programming communications interface 204 in communication with a personal computer 205. Persons skilled in the art will understand the nature of stimulation signal conversion and parameter customisation as presently employed in commercial hearing prosthesis systems.

The processed stimulation signals are wirelessly transmitted to the implanted component over a transcutaneous link 206. As illustrated, the various functions in the external component 200 are subject to control from a system controller 207.

Referring to Fig. 1 , in the implanted component 100, the stimulation signals are received 101. The received signals can also provide power to the implantable component. A processor 102 associated with the implant component controls circuitry associated with the electrodes 103 for providing the appropriate neural stimulation to the patient in accordance with the received stimulation signals. Typically, the implant component 100 is able to transmit telemetry data signals, pertaining to the operation of the implant component 100, back to the external component 200 so that the proper functioning of the implant component 100 can be monitored.

The above described functions are typical of a hearing neural stimulation system. However, the system has been adapted to measure and detect changes in certain physiological parameters of the implantee and issue an alert if the variation from the norm can be potentially diagnosed as symptomatic of a medical condition.

The present inventors have identified the possible need for remedial treatment for cochlear implant recipients in the first few weeks after surgery, when the risk of infection is at its greatest. Post-implant, a period of a few weeks is normally provided to allow the recipient's neurological sensitivity to electrical stimulation to stabilize. During such time, the main functional components of the system are not normally used until, at the end of the period, the clinical mapping procedure is conducted. This period of time provides a useful time when the normally inactive components can be used for a beneficial alternative purpose of detecting any symptoms of post-implant infection, for example.

Referring to Fig .2, electronics, such as an RC oscillator or piezo electric resonator and digital counting circuity, regularly or irregularly by way of pseudorandom circuitry, triggers the system to measure one or more specified physiological parameters and to store this data in a digital memory unit 208. Routine processing and statistical analysis of the stored data is performed by the system so as to determine the minimum, maximum, mean and trending characterises of each parameter and its co-relation coefficient with certain other physiological parameters.

The results of this analysis are then compared automatically every few minutes or so with data representing predetermined conditions associated as being symptomatic of a medical condition. Ideally, the predetermined data is programmed and stored in the memory 208 of the prosthesis via the programming communications interface 204. Such data could be prescribed by a health care professional as describing safe limits and variation beyond which a diagnosis of medical condition could be implied.

When one or, preferably, more certain combinations of measured physiological parameters exceed the stored limit, the system is configured to cause an external part of the prosthesis to issue a perceivable alarm, such as an acoustic alarm 209, to warm the user or, in the case of an infant, their parent or guardian.

Alternatively, the system can be arranged so as to convey this alarm to a remote electronic wireless receiver device such as mobile phone, a commercial broadcast receiver or a baby monitor like device from where a message can be delivered to a carer or guardian. A dedicated alarm or alerting system could flash a light and emit a beeping sound followed by the sound of an electronic synthesised voice describing the nature of the alert in plain language. Such examples might include, "WARNING your infant's breathing rate is dangerously low, apply CPR immediately", "Your baby is developing a fever that may be related to recent surgery, please consult a healthcare professional as soon as possible." or "Facial muscular spasms and low blood sugar detected, apply diabetic care strategy to your child now".

Another option, in the case of a hearing system, is to issue the alarm to the user in the form of stimulation signals applied by the electrodes 103 as stimuli.

Examples of the types of physiological parameters that are suitable for detecting a medical condition include: body temperature, respiration, heart rate, body and facial muscle activity, body tissue and fluid chemistry. The system is adapted to provide appropriate detectors or sensors for producing signals representative of the detected parameters. For certain parameters it is possible to adapt certain features of a normal prothesis system to additionally function as a detector. For other parameters an additional sensing transducer would need to be incorporated. Practical examples of how to adapt the system for the various parameters will now be described.

Body Temperature:

Incorporating a temperature sensor, such as a suitable form of thermoelectric sensor, into the implantable component 100 would allow direct monitoring of the body temperature so that the system could issue an alert in cases of overly high or low temperatures associated with a fever, for example.

Respiration and Vocal Sounds:

Small sized piezo electric microphones as used by the hearing aid industry have been adapted in prior art for implantable use. In practical experiments conducted by the present inventor, such implanted microphones, in combination with small sized piezo electric accelerometers from one hearing aid microphone manufacturer, have been found to successfully detect and characterise external sounds as well as internal body sounds and vibration from within the body. The slow repetitive detection of wide band acoustic noise from the sound pickup microphone of a sensitive hearing prosthesis can, for example, be used in quiet environments, as a means to detect the breathing sounds and vocalizations of an infant. Under particularly quiet conditions, it would be possible to use an external microphone, as opposed to an implanted microphone, to detect such breathing sounds and vocalizations. The repetition rate of the repetitive spectral characteristics of each inhalation-exhalation cycle can be determined using standard electronic digital signal processing techniques so as to allow abnormal breathing rates and changes to be detected. In this case, the system could be used to alert a carer if the breathing rate of an infant decreases significantly as it may with the onset of sudden infant death syndrome. In likewise fashion the spectrally limited vocalisations of a baby or infant user can be characterised then tracked for change in characteristics such as, but not limited to; occurrence rate, vocal pitch as well as the modulation amplitude and frequency applied by the larynx as a result of changing levels of emotional stress, discomfort or trauma.

Heart Rate and Blood Pressure:

Commercially available micro-electronic, piezo strain pressure transducers are small enough for use within the body. Hermetic encapsulation of such a transducer within a housing of titanium or other biocompatible material, and the provision of a pressure compliant diaphragm-like member between transducer and body fluid, can ensure hermeticity yet expose the transducer to pressure within the body. With suitable placement and calibration, information related to the user's heart rate and blood pressure can be conveyed to the processor 208 for processing and analysis. The small repetitive changes to the output of a pressure transducer incorporated within the implanted component, or similar such changes to the electrical impedance of body tissue between two implanted electrodes can be digitally processed to extract spectral features as a means to determine the rate and amplitude of the implantee's cardio-vascular activity as well as any changes which may preclude disease or onset of a potentially life threatening condition.

While healthy cardiac rhythms exhibit some degree of chaotic variability, those associated with certain cardiac diseases frequently exhibit periods of little variability, and are thus made detectable by this arrangement.

Body Tissue and Fluid Chemistry:

Small systematic changes to measured electrical impedance between stimulating electrodes 103 have been observed to result following periods of applied electrical stimulation. Such changes can be influenced by several factors including the history and nature of the electrical stimulation and the electrochemistry of the interface and intervening tissue.

Specific regimes of applied current can be employed to target the detection of specific body tissue and fluid changes as might occur during acute localised infection of an implantation site. In addition to this diagnostic regime it is anticipated that, from current developments and research into implantable blood chemistry sensors, thin film, biological antigen and blood sugar concentration sensing transducers are likely to become available in the foreseeable future. It is anticipated that such transducers would find suitable application with the present invention to supply the system with data that can in turn be used to detect abnormal physiological conditions for health care purposes.

Facial Muscular Activity:

The stimulating electrodes 103 of an implanted hearing prosthesis are used to receive low amplitude voltage signals representing the mymiographic potentials developed within the facial muscles during periods of activity. Digital signal processing by the system can be used to extract amplitude and spectral density information, which can in turn be used to infer facial muscular activity and potentially, the arousal level or onset of epilepsy of an infant user.

Head Movement Sensing:

The incorporation of one or more microphones and or accelerometers, as described previously, can be used to monitor accelerative head and or body movement. Movement data can then be processed and compared with data stored in the memory of the system such that abnormal movements, such as that of a child suffering an illness-induced discomfort, could be detected. Intentional movements by a user might also allow them to control their prosthesis. For example, the prosthesis could convey a synthesized voice as stimulus stating; "Attention remaining battery has reached 1 hour, please nod your head to confirm that you would like to change to a low stimulus rate to extend battery life another 8 hours".

In practice, the present invention has been found to be particularly suitable for use in neural stimulation hearing systems, such as cochlear implants. Such systems incorporate reasonably fast, modem programmable electronic data processing and storage electronics with external communications capabilities. In addition, hearing prostheses normally remain switched off during the first weeks after implantation, while the recipient's neurological sensitivity to electrical stimulation stabilizes and when the risk of post operative infection or tissue rejection is greatest. Therefore, as the electronic data gathering, storage, processing and conveyance capabilities of the implant system are not required for hearing during this period, these capabilities can be fully dedicated to execute the physiological parameter detection and processing at a time when post operative diagnostics and the detection of infection are most likely to benefit the user. By the time the hearing functionality of the prosthesis is required, the acute risk of infection is likely to be lower, such that the rate at which the system acquires physiological parameters for the purpose of detecting infection can be lowered so as not to cause any impact on the hearing functionality.

While the present invention has been described with respect to specific embodiments, it will be appreciated that various modifications and changes could be made without departing from the scope of the invention.

Claims

CLAIMS:

1. A medical prosthesis system, including: an implantable component configured to be implanted in a patient and apply stimulation to said patient based upon processed stimulation signals; a processor for producing said processed stimulation signals; and one or more detectors for detecting one or more physiological parameters of said patient and producing physiological parameter signals representative of said detected parameters; wherein said processor is configured to receive said physiological parameter signals and perform an analysis operation to determine whether said detected parameters meet predetermined conditions representative of a specific physiological condition, wherein if said predetermined conditions are determined to have been met said system provides an alarm or other indication that a specific physiological condition has been detected.

2. The system according to claim 1 , wherein said one or more detectors includes a temperature sensor incorporated in said implantable component for sensing body temperature of said patient.

3. The system according to claim 1 or 2, wherein said one or more detectors includes a microphone for detecting sounds of said patient breathing or vocalizing.

4. The system according to any one of the preceding claims, wherein said one or more detectors includes a pressure sensor incorporated in said implantable component for detecting the pulse of said patient.

5. The system according to any one of the preceding claims, wherein said one or more detectors includes electrodes incorporated in said implantable component.

6. The system according to claim 5, wherein said electrodes are configured to detect electrical impedance of body tissue.

7. The system according to claim 5 or 6, wherein said electrodes are configured to detect voltages generated by neural and/or muscular activity.

8. The system according to any one of the preceding claims, wherein said one or more detectors includes a biological antigen senor incorporated in said implantable component.

9. The system according to any one of the preceding claims, wherein said one or more detectors includes a blood sugar concentration sensor incorporated in said implantable component.

10. The system according to any one of the preceding claims, wherein said one or more detectors includes an accelerometer incorporated in said implantable component for detecting accelerated body movement of said patient.

11. The system according to any one of the preceding claims, further including a memory for storing said physiological parameter signals.

12. The system according to claim 11 , wherein said processor refers to stored physiological parameter signals when performing said analysis operation on current physiological parameter signals.

13. The system according to any one of the preceding claims, further including an alarm unit for receiving said indication and providing a perceivable alarm.

14. The system according to any one of the preceding claims, wherein said system is an auditory neural stimulation system.

15. The system according to claim 14, wherein said indication is alerted to said patient by way of audible stimulation signals applied by said implantable component.