Abstract:
An apparatus is disclosed that provides an implantable sensor assembly configured with signal conditioning circuitry positioned between a sensor and connector to form a unitary liquid impervious flexible structure. The connector is adapted to be detachably connected to an implant service unit, which service unit provides battery power, control functions and wireless communication with a base station. The sensor unit is modular in nature and allows for easy exchange with the implant service unit and other sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 USC § 119 (e) from U.S. provisional application Ser. No. 60/958,077 field Jul. 2, 2007 and titled “Implantable Sensor and Connecter Assembly”. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A “SEQUENCE LISTING” 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention relates to implantable telemetric systems, and more particularly it relates to a system and method for implanting and detachably connecting a sensor to a telemetric implant in an enhanced fashion that avoids high impendence and other problems inherent in such systems in the past. 
         [0006]    2. Background of the Invention 
         [0007]    In conducting scientific studies and providing treatment implantable sensors are used for both animal research and human monitoring, and these sensors exist in a variety of forms. Normally these sensors, such as piezoresistive blood pressure or temperature sensors, or bioelectric signal sensors are either connected directly to the implant, or are connected via an implantable connector. Ordinarily, the implant contains circuitry that provides power and signal conditioning to the sensors. 
         [0008]    Implantable systems with easily detachable connectors add a high degree of flexibility to the system by allowing the quick replacement of a damaged sensor or the selection of a sensor with different characteristics. There are though a number of problems that are introduced by the use of an implantable connector to connect physiological sensors to an implant. The majority of these problems are caused by the high impedance inherent in these sensors. This high impedance when affected by the implantation connector system causes DC drift, alteration of the true value of the sensor measurement, etc. 
         [0009]      FIG. 1  is a schematic diagram depicting a prior art configuration of senor connector assembly  20  with a sensor  21  and connector assembly  23  and  24  that connects sensor  21  to a patient monitor  29  as indicated by U.S. Pat. No. 5,568,815. The amplifier and temperature compensation circuitry  27  are located before the patient monitor display  29 . This system is not suitable for implantation, since the electrical connector assembly  23  and  24  does not have any provisions for providing a low impedance interface to the sensor connector assembly. Sensor  21  lead  32  comes out of the body  30  through skin  31  before the first connection is made and therefore the electrical connector does not come into contact with body fluids. This will not be the case in an implantable system and this sensor assembly would not be usable in such a case. 
         [0010]    Similarly, patent application US2007/0106165A in  FIG. 2 , discloses a similar sensor assembly  41  that incorporates the amplifier and temperature compensation circuitry  45  in connector  47  of connector set  46  and  47  outside the patient&#39;s body  49  before it connects to monitor display  51 . Again this arrangement will only work in a non-implantable situation, were the connector is outside the body and not in contact with body fluids. 
         [0011]    Interfacing a physiological sensor that has high impedance such as a piezoresistive blood pressure sensor to an implant via a connector, which is then placed into an animal may cause small changes in the value of the piezoresistive elements comprising the sensor. These small impedance changes are due to moisture trapped inside the connector which when placed inside the warm animal body cause the microenvironment inside the connector to change. These changes to the sensor impedance are small, but the normal changes to the impedance of the sensor to changes in blood pressure are also small, in the order of 2-3% for a full scale change of physiological range blood pressure. These small changes in impedance can create significant errors in readings taken by the sensor. These errors are of such an extent that readings obtained by the sensor will have no useful value. 
         [0012]    Such changes due to the moisture effect manifest as a slow and unpredictable drift of the pressure signal with either a positive and/or a negative sign. Although there are methods that can be used to prevent such moisture generation and buildup, such as filling the connector with silicone oil, or mineral oil, these measures are time consuming and not always able to remain viable. Also they might impede with the normal use of the connector insulation. 
         [0013]    Thus what is needed is a fully implantable modular biotelemetric monitoring system that does not have the disadvantages of the prior art that made it impossible to provide detachable piezoresistive that did not suffer form signal degradation. 
       SUMMARY 
       [0014]    Thus, it is an objective of the present invention to provide a fully implantable modular biotelemetric monitoring system with detachable connectors to all allow the changing of sensors. 
         [0015]    These problems are alleviated by the use of an impedance converter circuit that converts the high sensor impedance to very low impedance prior to the signal passing through a connector junction. 
         [0016]    The present invention achieves these and other objectives by providing: an implantable telemetric sensor system having: a) a sensor assembly including a sensor, signal conditioning circuitry and a connector all in a sealed liquid impervious package; b) an implant service package with a power supply to power the implant service unit, a microcontroller to control operation of the implant service unit, memory for storing software to run the implant service unit with the microcontroller, a transceiver for communicating with a base unit and a connector capable of forming a liquid impervious detachable electrical connection with the sensor connector of the sensor assembly; and c) wherein when the sensor assembly is implanted inside a living biological system and the sensor is connected to monitor a function of the biological system and the connector is attached to a connector of the implant service package. 
         [0017]    In a further aspect of the present invention the conditioning circuitry includes circuitry for amplifying signals generated by the sensor. In yet another aspect of the present invention the conditioning circuitry includes temperature compensating circuitry. In yet another aspect of the present invention the conditioning circuitry includes circuitry for changing the impedance of signals generated by the sensor. Yet still another aspect of the present invention the sensor assembly is pressure sensor that uses a piezoresistive surface for sensing pressure. 
         [0018]    In a further aspect of the present invention it provides an implantable sensor assembly having: a) a sensor in electronic communication with conditioning circuitry and the conditioning circuitry is electrical communication with a connector, and wherein the sensor, the conditioning circuitry and the connector are joint as one unit in a liquid impervious sealed package; and b) the connector of the sensor assembly is configured to form a detachable liquid impervious detachable connection with a connector of an implant service unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0019]    The invention will be better understood by an examination of the following description, together with the accompanying drawings, in which: 
           [0020]      FIG. 1  a schematic diagram of a prior art sensor connector assembly array; 
           [0021]      FIG. 2  a schematic diagram of another prior art sensor connector assembly array; 
           [0022]      FIG. 3  a diagram of a preferred embodiment of the sensor connector assembly array of the present invention; 
           [0023]      FIG. 4  is a plan view of a preferred embodiment of a sensor assembly made according to the present invention; 
           [0024]      FIG. 5  is a plan view of another sensor assembly made according to the present invention; and 
           [0025]      FIG. 6  is a plan view of the complete components of the system of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Interfacing a physiological sensor that has high impedance such as a piezoresistive blood pressure sensor to an implant via a connector, which is then placed into an animal may cause small changes in the value of the piezoresistive elements comprising the sensor. These small impedance changes are due to moisture trapped inside the connector which when placed inside the warm animal body cause the microenvironment inside the connector to change. These changes to the sensor impedance are small, but the normal changes to the impedance of the sensor to changes in blood pressure are also small, in the order of 2-3% for a full scale change of physiological range blood pressure. 
         [0027]    Such changes due to the moisture effect manifest as a slow drift of the pressure signal with either a positive and/or a negative sign. Although there are methods that can be used to prevent such moisture generation and buildup, such as filling the connector with silicone oil, or mineral oil, these measures are time consuming and not always able to remain viable. Also they might impede with the normal use of the connector insulation. 
         [0028]    The impedance converter circuit built into the sensor of the present invention between the sensor and its connector provides amplification and conversion of the differential signal into a unipolar signal and also converts the high impedance (about 3 kOhm to 100 kOhm) to low impedance (about 0.1 Ohm or less). 
         [0029]      FIG. 3  is a schematic diagram of a preferred embodiment of implantable biotelemetry system  71  of the present invention. The entire system  71  is of a compact size which allows it to be completely implanted within the body  73  of a biological system typically an animal that is under study. The animal can vary from large animals such as cows or a sheep down to dogs and rats. The system typically has a variety of sensors to measure blood pressure, blood flow, and temperature as well as EKG sensors. Standard sensors for flow can be used such as Doppler ultrasound or transit time ultrasound sensors to measure blood flow, etc. Pressure can be measured with piezoresisteive based pressure sensors. 
         [0030]    The parts of the implantable biotelemetry system  71  are a sensor assembly  74  and an implant service unit  79 . The sensor assembly  74  consists of a sensor  75  which connects by lead  77  to amplifier, temperature compensation and impedance conversion circuitry  79 , which in turn connects to connector  81 . Sensor  77  circuitry  79  and connector  81  form a unitary liquid impervious sealed unit. The only exposure to the outside environment is senor  75 . Implant service unit  79  consists of implant  83  which connects by lead  85  to connector  87 . Connectors  81  and  87  are configured to detachably and securely fit together to form a sealed liquid impervious connection. 
         [0031]    As noted above implantable biotelemetry system  71  is encased in a liquid impervious sealed package which allows it to be wholly implanted within the body  73  to of a biological subject. As noted above amplifier/temperature compensation circuitry is located at the sensor side within sensor assembly  74  of the implant before connector  81  to thereby condition the signal before it passes through connector  81 - 87  junction. As noted above this conditions the signal and thus avoids the degradation of the data quality of the signal that a high impedance unconditioned signal could very well experience as it passes through the junction formed by connectors  81 - 87 . This allows for a highly flexible implantable biotelemetry system  71  in which different sensor arrays  74  can be attached or detached to implant service unit  80 . Therefore providing the signal generated by sensor  75  with amplification, temperature compensation and impedance conversion before the signal passes through connector  81 - 87  junction is an important attribute of the present invention. This makes the arrangement of the connector and amplifier/temperature compensation module clearly very crucial in an implantable system. 
         [0032]      FIG. 4  is a view of a preferred embodiment of a pressure sensor assembly  90  (unit  74   FIG. 3 ) of the present invention. It consists of pressure probe  91  with a pressure sensor  93  connected to electrical lead  95 . Electrical lead  95  connects to amplifier, temperature compensation and impedance conversion circuitry  97 . Electrical lead  99  connects amplifier, temperature compensation and impedance conversion circuitry  97  to connector  101 . 
         [0033]    Unit  90  is completely sealed with the only exposed part being a surface of sensor  93 , in the case of this particular unit, to obtain the appropriate pressure readings. Electrical lead  91  is encased in a liquid impervious highly flexible biocompatible material  100  such as silicon covering. The liquid impervious covering  100  forms a unitary connection to the covering  102  of circuitry  97  a highly flexible liquid impervious biocompatible material such as medical grade silicon. To further protect circuitry  97  it has surrounding the circuitry  97  under the outside silicon layer  102  is shrink wrap tubing  103 . Lead  99  similarly has a highly flexible liquid impervious covering  105  that forms a unitary connection with covering  102  of circuitry  97 . 
         [0034]    The dimensions of pressure sensor unit  90  are as follows: a) sensor  93  is 1.2 mm in diameter and 4 mm in length, b) lead  91  is 20 cm long, c) circuitry unit  97  is 7 mm in diameter and 3 cm long, d) lead  91  is 12.5 cm long and 2.5 mm wide, and e) connector  101  is 3.5 cm long and at its greatest diameter 6 mm in diameter. These sizes have only been provided to give some conception of a possible configuration of unit  90 . Those skilled in the art will realize that the dimensions of unit  90  can be made much smaller or larger depending on the application and size of the animal under study. Sensor unit  90  is a highly flexible and pliable unit which allows it to be easily implanted in a subject animal&#39;s body without causing discomfort or disruption to the animal. 
         [0035]    In the preferred embodiment depicted in  FIG. 4  pressure probe  91  is a pressure probe made by Millar Laboratories of Huston Tex. Sensor  93  has a piezoresistive sensor  105 . When unit  90  is implanted in a subject animal sensor  93  is inserted in to the specific artery of the subject animal to obtain the desired pressure readings. Amplifier, temperature compensation and impedance converter circuit  97  is standard circuitry well known in the art so a discussion of its specific makeup is not necessary since those skilled in the art would know how to design such circuits. Naturally, the amplifier circuitry would be increasing the strength of the signal and the impedance converter would be decreasing the impedance of the signal. Additionally, those skilled in the art will also know how to miniaturize such circuits on a silicon chip or otherwise so a discussion of how to fabricate them is not necessary for this disclosure. 
         [0036]      FIG. 5  is an example of an EKG sensor unit  110  made according to the present invention. Unit  110  has similar dimensions to unit  90  of  FIG. 4 . Electrical leads  111  and  112  connect to amplifier, temperature compensation and impedance conversion circuitry  115  which in turn through lead  117  connects to connector  119 . Electrical leads  111  and  112  have tips  111 T and  112 T with bear wires which can be attached to the appropriate interior portion of the subject animal to obtain signals for monitoring the subject animal with an EKG. Starting at point  111 C and  112 C and moving towards circuit  115  leads  111  and  112  are covered with a liquid impervious biocompatible covering which is a uniform unbroken covering all the way to connector  119 , the same as it is on sensor unit  90 . Likewise in all other respects sensor unit  110  is similar to sensor unit  90 . Sensor unit  110  is a highly flexible and pliable unit which allows it to be easily implanted in a subject animal&#39;s body without causing discomfort or disruption to the animal and its activities. 
         [0037]    As schematically shown in  FIG. 3  sensor unit  71  connects to an implant service unit  80  both of which are wholly implanted in the body  73  of the animal under its skin  72 .  FIG. 6  is a plan view of a preferred embodiment of a service unit  120  with power pack  127 . Service unit  120  contains a microcontroller, wireless transceiver unit, computer memory, other circuitry and software, all of which is not shown to control operation of sensors attached to unit  120 . Unit  120  transmits data gathered by the sensors to a separate base station or stations, also not shown. Operation of unit  120  is controlled through the base station. In turn the base station would typically connect to a PC or other computer from which actual control would be maintained. The PC would be running appropriate software to allow the PC user to exert control over unit  120  and its attached sensors, gather the data from the sensors. The software on the computer would also store and analyze the data gathered. The microcontroller, wireless transceiver, memory, other ancillary circuitry and software is not shown or discussed in further detail since all are well known the art and can be implemented in a wide variety of ways. 
         [0038]    Unit  120  in addition to lead  125  which connects it to power supply  127  has four other leads  121 ,  122 ,  123  and  124  with connectors  131 ,  132 ,  133  and  134  respectively. Unit  120  can control and monitor vital functions of the subject animal, not shown, on four different channels with four different sensors. As depicted in  FIG. 6  connectors  132  and  134  do not have any sensors units attached to them. Connector  133  is connected to connector  101  of sensor  90 . In  FIG. 6  only connector  101  and lead  99  of pressure sensor are shown. Service unit  120 , electrical lead  125  to power supply  127  and all of the leads  121 ,  122 ,  123  and  124  are covered by a liquid impervious layer, such as silicon. Also, connectors  131 ,  132 ,  133  and  134  all for a detachable secure liquid impervious connection with the connectors of each of the sensor units that connect to them. 
         [0039]    Connected to lead  122  is an ultrasound Doppler sensor  142  for monitoring blood flow. Sensor head  145  is secured around a blood vessel with suture threads  15 ,  152  and  153 . Sensor head  145  connects to connector  141  by electrical lead  143 . Connector  141  forms a detachable liquid impervious connection to connector  131  of lead  122 . Ultrasound Doppler sensor  142  is covered by an appropriate liquid impervious covering such as silicon. 
         [0040]    In one variation of the preferred embodiment service unit  120  is 5 cm long, 2.25 cm wide and 6 mm high. Power unit  127  is 5 cm long and 1.7 cm in diameter, the connectors and all of the connectors and leads to the connectors are 5 cm long. These dimensions can vary depending on the application. In the preferred embodiment lead  125  has a connector junction  161  formed by connectors  163  and  165  which form a detachable but secure and liquid impervious connection. 
         [0041]    Thus, as described the present invention provides a modular compact and fully implantable biotelemetric monitoring system. 
         [0042]    While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made to it without departing from the spirit and scope of the invention.