Abstract:
A medical therapy system including liquid detection is disclosed. A medical therapy includes a case with an interior and an exterior. Within the interior of the case is the liquid detection system that includes a first electrode set with a first positive electrode and a first negative electrode. The liquid detection system further includes an impedance measurement circuit coupled to the first electrode set to determine impedance values between the first positive electrode and the first negative electrode. A threshold detector compares impedance values between the first electrode set to a first threshold impedance. A microprocessor is programmed to initiate an alarm when measured impedance from the first electrode set is below the first threshold impedance.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to portable external infusion systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Diabetes is a disease in which the body does not produce or properly use insulin. Approximately 13 million people in the United States have been diagnosed with some form of diabetes. Type 1 diabetes results from the body&#39;s failure to produce insulin. Type 2 diabetes results from insulin resistance in which the body fails to properly use insulin. To effectively manage the disease, diabetics must closely monitor and manage their blood glucose levels through exercise, diet and medication. In particular, both Type 1 and Type 2 diabetics rely on insulin delivery to control their diabetes. Traditionally, insulin has been injected with a syringe multiple times during the day, usually self-administered by the diabetic. In recent years, external infusion pump therapy has been increasing, especially for delivering insulin to diabetics using devices worn on a belt, in a pocket, or the like, with the insulin delivered from a reservoir via a catheter with a percutaneous needle or cannula placed in the subcutaneous tissue. 
         [0003]    External infusion devices allow Type 1 and Type 2 diabetics to better manage and control their diabetes. The external infusion device is intended to be used continuously and delivers insulin twenty-four hours a day according to a programmed plan unique to each pump wearer. A small amount of insulin, or a basal rate, is given continually. This insulin keeps the user&#39;s blood glucose levels in the desired range between meals and overnight. When food is eaten, the user programs the external infusion device to deliver a bolus of insulin matched to the amount of food that will be consumed. The user determines how much insulin will be given based on factors including insulin sensitivity, insulin duration, insulin-on-board, and the like. In many instances, external infusion devices include a processor that assists the user in making therapy decisions based on information provided by the user including blood glucose levels, carbohydrate intake, and/or information from the external infusion device. Exemplary devices are described in U.S. Pat. No. 6,554,798 issued on Apr. 29, 2003 to Mann et al., and entitled “External Infusion Device with Remote Programming, Bolus Estimator and/or Vibration Alarm Capabilities,” which is specifically incorporated by reference herein. 
         [0004]    Users of external infusion device therapy rely on the precision and control of the therapy. It is important to minimize unexpected compromises of the infusion device, such as unnoticed cracks that allow liquids to leak into the device. Such leaks could lead to unpredictable device behavior or even failure of the device. Thus, having reliable and robust leak detection is highly desirable so users can engage in activities such as bathing, showering or even walking in the rain without compromising their confidence in the reliability of their external infusion device. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    In one embodiment a medical therapy system including liquid detection is disclosed. A medical therapy includes a case with an interior and an exterior. Within the interior of the case is the liquid detection system that includes a first electrode set with a first positive electrode and a first negative electrode. The liquid detection system further includes an impedance measurement circuit coupled to the first electrode set to determine impedance values between the first positive electrode and the first negative electrode. A threshold detector compares impedance values between the first electrode set to a first threshold impedance. A microprocessor is programmed to initiate an alarm when measured impedance from the first electrode set is below the first threshold impedance. 
         [0006]    In another embodiment a method of detecting fluid is disclosed. The method includes an operation that sets a first threshold impedance. In another operation impedance between a first set of electrodes is measured. Another operation stores the measured impedance to a memory while still another operation compares the measured impedance to the first threshold impedance. The method activates an alarm if the measured impedance is below the threshold impedance. 
         [0007]    Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A detailed description of embodiments of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the several figures. 
           [0009]      FIG. 1A  is an exemplary illustration of elements within an infusion system, in accordance with embodiments of the present invention. 
           [0010]      FIG. 1B  is an additional embodiment of an infusion pump that can be used within the infusion system, in accordance with embodiments of the present invention. 
           [0011]      FIG. 1C  is still a further embodiment of an infusion system, in accordance with embodiments of the present invention. 
           [0012]      FIG. 2  is an exemplary block diagram of a liquid detection system for use in portable electronic devices, in accordance with embodiments of the present invention. 
           [0013]      FIG. 3  is a flow chart illustrating exemplary operation of the liquid detection system, in accordance with embodiments of the present invention. 
           [0014]      FIGS. 4A and 4B  are exemplary illustrations of a sensor set and transmitter that can be used in conjunction with the infusion system, in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    As shown in the drawings for purposes of illustration, the invention is embodied as an element or component within a portable infusion system. While many embodiments describe measuring impedance between electrodes to determine the presence of liquid, the extent of the disclosure should not be construed to exclude measuring capacitance, inductance or resistance to accomplish the same objective. Rather, impedance along with capacitance, inductance, and resistance should all be considered interchangeable to those skilled in the art as being able to determine whether liquid is present on electrodes. 
         [0016]      FIG. 1A  is an exemplary illustration of elements within an infusion system  100 , in accordance with embodiments of the present invention. The infusion system  100  includes an infusion pump  101  having a case  102  that contains a reservoir  104 . The infusion pump  101  includes a mechanism that moves fluid from the reservoir  104  to an infusion set  108  via tubing  106 . In some embodiments the infusion set  108  includes a cannula (not shown) that is coupled to the tubing  106  to deliver fluid from the infusion pump  101  into subcutaneous tissue of a user. When used for diabetes therapy, the reservoir  104  can be filled with insulin to be delivered via the infusion set  108 . 
         [0017]    In some embodiments the case  102  is made from polycarbonate, acrylonitrile butadiene styrene (ABS), or copolyester materials such as Eastman TRITAN to increase durability and to minimize the likelihood of liquid ingress such as water. In one embodiment, during the manufacturing process the case  102  is ultrasonically welded to completely seal major openings in the case. However, the case  102  does include other openings such as those for the reservoir  104  and battery, which are protected against liquid ingress by flexible o-rings with interference fits to their mating components. Furthermore, the reservoir  104  is designed to minimize the likelihood of fluid from the reservoir  104  leaking into the case  102 . However, regardless of how robust and durable the case  102  and reservoir  104  are designed, real world usage can include repeated drops, crushes and pressure fluctuations that can eventually compromise the integrity of the case  102 . 
         [0018]      FIG. 1B  is an additional embodiment of an infusion pump  101 ′ that can be used within the infusion system  100 , in accordance with embodiments of the present invention. Infusion pump  101 ′ includes a case  110  that is similar to the case  102 . Similar design features and manufacturing techniques can be applied to both cases  102  and  110 . For example, case  110  includes an opening  112  for a reservoir (not shown). Case  110  further includes an opening that is sealed by battery cap  114 . Within the case  110  are electronics and mechanism that control the flow of fluid from the reservoir to the infusion set. 
         [0019]      FIG. 1C  is still a further embodiment of an infusion system  100 ′, in accordance with embodiments of the present invention. The infusion system  100 ′ shown in  FIG. 1C  is commonly referred to as a “patch pump”. As illustrated, infusion system  100 ′ lacks the tubing and infusion set found in infusion system  100  in  FIG. 1A . Rather, in some embodiments, the infusion system  100 ′ includes a cannula  116  that can be inserted to various depths within the user. A reservoir is contained within a case  118  of the infusion system  100 ′. The case  114  further contains electronics and mechanism that control dispensing of fluid within the reservoir through the cannula  116 . 
         [0020]    In embodiments where the infusion system  100 ,  100 ′, or infusion pump  101 ′ is used for diabetes therapy the user relies on precision control provided by the electronics within the infusion pump  101 . Accordingly, integrity of the respective cases is important to protect sensitive electronics within the case from exposure to liquid. Liquid within the case can compromise the entire infusion system leading to malfunctions, unpredictable behavior or even complete failure of the infusion pump. As users rely on the infusion system to regulate blood sugar, detection and notification of the user regarding liquid in the pump case results in users having an opportunity to contact customer service to troubleshoot potential issues with the infusion system before catastrophic failure occurs. 
         [0021]      FIG. 2  is an exemplary block diagram of a liquid detection system for use in portable electronic devices, in accordance with embodiments of the present invention. The liquid detection system includes electrodes  200   a  and  200   b  that are connected to impedance circuitry  202 . The impedance circuitry  202  is coupled to a threshold detector  204  which in turn is coupled to a microprocessor  206  having a memory  210 . In some embodiments the impedance circuitry  202  is further optionally directly coupled to the microprocessor  206 . In all embodiments, the microprocessor  206  is used to control an alarm  208 . In one embodiment the microprocessor  206  is dedicated to the liquid detection system. In other embodiments the microprocessor  206  also performs additional processing for the infusion system. 
         [0022]    In one embodiment electrodes  200   a  and  200   b  are comb shaped electrodes that include teeth that are offset as shown in  FIG. 2 . For purposes of illustration only, electrode  200   a  is shown as a positive electrode while electrode  200   b  is the negative electrode. When dry, the electrical impedance between electrodes  200   a  and  200   b  is greater than 100 mega Ohm. If liquid is introduced across the offset combs the impedance between the electrodes  200   a  and  200   b  is significantly reduced. The impedance circuitry  202  periodically converts the impedance into a measureable form, such as voltage or a digital value. The value from the impedance circuitry  202  is analyzed by the threshold detector  204  that sends a wake-up signal to the microprocessor  206  when a threshold impedance is measured across the electrodes  200   a  and  200   b . Alternatively, periodic impedance values from the impedance measurement circuitry  202  can be recorded into the memory  210  of the microprocessor  206 . The microprocessor  206  can further include software, hardware, or combinations thereof to analyze impedance values stored within the memory  210  for patterns to determine if there is liquid on the electrodes or if the circuit is simply in a high humidity environment. The illustration of the electrodes  200   a  and  200   b  as offset combs should not be construed as limiting. In other embodiments different electrode configurations can be used so long as liquid across the electrodes  200   a  and  200   b  creates a detectable change in impedance. 
         [0023]    In some embodiments the threshold detector  204  is set low enough that impedance values caused by a worst case humidity condition does not trigger the wakeup to the microprocessor  206 . For example, based on the operating parameters of the infusion system, the infusion pump can be placed in a maximum humidity environment with liquid detection circuits throughout the interior of the case. The minimum impedance values for the liquid detection circuits can be measured when the pump is operated within the maximum humidity environment thereby establishing a threshold value. 
         [0024]    In other embodiments, the threshold detector  204  is set so a relatively high impedance value triggers the wakeup function of the microprocessor  206 . In these embodiments, the wakeup function additionally activates the optional logging and analysis of impedance values to determine if fluctuations in ambient humidity caused the initial threshold detection. This embodiment can be beneficial for portable electronic systems because it can reduce power draw from the liquid detection circuit. Thus, when a relatively high threshold impedance value is registered, the liquid detection circuit begins recording impedance values in order to create an impedance history that can be analyzed for patterns caused by fluctuations in ambient humidity. 
         [0025]    In still further embodiments, impedance values can be correlated to time using a clock  212  in order to create a dynamic threshold based on previous temporal impedance measurements. For example, the liquid detection circuit measures and records impedance values that decrease between 8 AM and 2 PM corresponding to increasing ambient humidity. Accordingly, the following day, the threshold values can be dynamically changed to reflect the ambient humidity of the previous day. Thus, as the humidity increases and decreases throughout the day, the threshold impedance value can dynamically change based on previously recorded data to avoid false alarms. Another technique that can be used to compensate for humidity and avoid false alarms of liquid on the electrodes is to monitor the rate of change of impedance. 
         [0026]    Other embodiments include optional communication module  214  coupled with the microprocessor  206 . The communication module  214  can include, but is not limited to wireless communication protocols such as Wi-Fi, BLUETOOH, BLUETOOTH LOW ENERGY, ZIGBEE, Z-WAVE, LTE and NFC. The communication module  214  enables access to location information along with corresponding weather data and weather forecasts that can be utilized to dynamically change the threshold impedance value of the liquid detection system. 
         [0027]    In some embodiments, when the liquid detection system shown in  FIG. 2  is applied to the infusion systems in  FIGS. 1A-1C  there may be additional sets of electrodes  200   a  and  200   b  placed at various locations within various compartments within the respective cases. Furthermore, both the threshold detector and the microprocessor can be programmed with different threshold impedances based on the location of electrodes. In one example, liquid detection electrodes can be located near the reservoir for infusion pump  101  and  101 ′. Upon being filled and installed within the infusion pump  101  the reservoir itself may contain insulin that was recently removed from a refrigerated space. Accordingly, as the insulin within the reservoir warms to ambient temperature condensation may form on the outside of the reservoir. As this is a known issue, the reservoir chamber is properly sealed and vented to allow potential condensate to naturally evaporate. To avoid false detection of fluid within the infusion pump the threshold impedance for the electrodes within the reservoir chamber may be very low. However, to ensure that any fluid within the reservoir chamber does not migrate to an originally sealed compartment, the threshold impedance values for another set of liquid detection electrodes may have a very high impedance threshold. In another embodiment, collection of impedance values from liquid detection electrodes within the reservoir chamber is paused for a period of time after a reservoir is installed. Similar features can also be used within and adjacent to the battery compartment to avoid false liquid detection upon replacement of the battery. 
         [0028]      FIG. 3  is a flow chart illustrating exemplary operation of the liquid detection system, in accordance with embodiments of the present invention. The flow chart beings with operation  300  that sets an impedance threshold. As previously discussed, in various embodiments multiple threshold impedance values can be set for multiple liquid detection electrodes. Likewise, the threshold impedance can also by dynamically set based on previously measured values or weather forecasts. Operation  302  measures impedance between the liquid detection electrodes and can be initiated by a variety of triggers such as software or hardware timers. In still other embodiments where power consumption is not an issue or for extremely critical components impedance measurement can be taken continuously. In various embodiments the interval between impedance measurements is between one minute and 30 minutes. In some embodiments the interval between impedance measurements varies based on the time of day. For example, during regular sleeping hours the liquid detection system may only take an impedance measurement every 15 or 30 minutes. Conversely, during regular waking hours impedance measurements can be taken more frequently such as, but not limited to every minute or every five minutes. To accommodate various work schedules, in other embodiments a user is allowed to specify sleep and wake hours. 
         [0029]    In some embodiments if operation  302  is initiated via software, operation  308  records the measured impedance to memory. In embodiments where operation  302  is initiated by hardware, the measured impedance is passed to a threshold detector circuit  318  that executes operation  320  to determine if the rate of change of impedance is indicative of liquid in the case. If operation  320  indicates liquid is in the case operation  310  wakes up the processor and operation  306  records the measured impedance to memory. In many embodiments regardless of whether the trigger of operation  302  is hardware, software or combinations of both, a time associated with the impedance measurement is also recorded into memory. 
         [0030]    Operation  312  applies a fluid detection algorithm to the impedance values stored in memory resulting in operation  314  that determines if liquid is detected. If operation  314  detects liquid operation  316  activates an alarm. The alarm that is activated can be audible, tactile (vibration), visual or a combination thereof. If operation  314  does not detect liquid, operation  308  waits until the next impedance measurement is taken via operation  302 . 
         [0031]      FIGS. 4A and 4B  are exemplary illustration of a sensor set  400  and transmitter  402  that can be used in conjunction with the infusion system, in accordance with embodiments of the present invention. The sensor set  400  includes a sensor (not shown) that in some embodiments is inserted into subcutaneous tissue of a user. The sensor set  400  further includes a connector  404  that is coupled to the sensor. The sensor includes multiple electrodes that are coupled to corresponding contacts on the connector  404 . The transmitter  402  includes a port  406  that receives to connector  404 . Within the port  406  are pins that mate with the connector  404  contacts. The pins within the transmitter are coupled to a circuit board that includes a power supply and electronic circuitry that enables operation of the sensor set  400  and wireless transmission of data from the sensor  400  to the infusion system.  FIG. 4B  shows coupling of the transmitter  402  to the sensor set  400  after the sensor set  400  has been inserted into the user. Coupling of the transmitter is accomplished by supporting the sensor set  400  while moving the transmitter  402  in direction D 1  while aligning the port and connector. 
         [0032]    In many embodiments a power supply within the transmitter  402  allows the transmitter to be reused with multiple sensors before being disposed of or alternatively being recharged. However, when the sensor is inserted into the user it is possible, however unlikely, for bodily fluid such as blood to be released from the insertion site. Thus, due to the possible introduction of fluid near the port  406  it would be beneficial to include a fluid detection system within the transmitter  402 . Accordingly, the fluid detection system described above should not be construed to be used exclusively with infusion systems, subcutaneous sensors, or even electronic devices having cases. Instead, the fluid detection system described above could be used in any application requiring the detection of liquid. Examples include, but are not limited to detection of undesirable liquid leakage proximate to intravenous injection sites or catheter sites. In still other embodiments, the liquid detection system could be adapted to measure humidity based on impedance between the electrodes. 
         [0033]    While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.