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Method to sense temperature in an implantable pumpRelated Patent Categories: Pumps, With Signal, Indicator, Or Inspection MeansMethod to sense temperature in an implantable pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080063539, Method to sense temperature in an implantable pump. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This is a continuation of U.S. patent application Ser. No. 09/950,154, filed Sep. 10, 2001, which is incorporated herein by reference in its entirety and which is a continuation-in-part application of U.S. patent application Ser. No. 09/302,517, filed Apr. 30, 1999, to which priority is claimed. FIELD OF THE INVENTION [0002] This invention relates to implantable drug infusion pumps. In particular, this invention relates to a method and apparatus for continuously sensing and recording temperature of an implantable infusion pump. BACKGROUND OF THE INVENTION [0003] Implanted infusion pumps deliver therapeutic drugs to a patient according to a computer program executed by a processor that is programmed with drug dosing parameters. Some infusion pumps use a microprocessor to control a small, positive displacement pump according to programming instructions delivered to the microprocessor through an RF programming link so as to permit the implantable pump to be remotely programmed and operated. Other infusion pumps use compressed-gas propellants instead of a pump to deliver a drug. [0004] Most medical devices, including infusion pumps, are specified to be stored in a particular not-to-be-exceeded temperature range. Storage temperatures outside the manufacturer's specified storage temperature range can damage implantable infusion pumps and for this reason, precautions are normally taken to insure that an implantable infusion pump is not inadvertently subjected to adversely high or low temperatures. Monitoring a pump's temperature over time would provide a mechanism by which damaging temperature extremes could be identified prior to implantation. [0005] In addition, a pump that includes a mechanism by which the pump's temperature can be monitored might provide drug-delivery performance improvements. The flow characteristics of mechanical pumps are often temperature sensitive. Temperature compensation of undesirable flow changes can be achieved using the electrical temperature signal to adjust the flow via the internal controller. [0006] Furthermore, monitoring patient temperature by an infusion pump, either remotely, for example at the distal end of a catheter connected to the pump, or at the pump, might allow for drug therapy delivery to be modified according to the patient's measured temperature, improving the effectiveness of the therapy. BRIEF SUMMARY OF THE INVENTION [0007] An implantable drug infusion pump is made more reliable and its performance is improved by inclusion of a temperature sensor in the pump, which monitors the pump's temperature. Undesirable temperature dependencies in an infusion pump's performance can be reduced or eliminated by measuring the pump's actual temperature using a separate temperature sensor and adjusting the pump's operation accordingly by way of a computer program designed to modify pump performance according to temperature variations. Drug therapy administered by an infusion pump can be automatically or manually adjusted according to the pump's actual temperature. [0008] In the preferred embodiment, a thermistor, embedded within a pump at an empirically determined optimum location to monitor the overall temperature of the pump's constituent mechanisms, is operatively coupled to the pump's control microprocessor. The microprocessor's control program is written to read the thermistor's resistance and from the temperature-dependent resistance of the thermistor, calculate the pump's temperature. [0009] In at least one alternate embodiment, a temperature sensor external to the infusion pump can be used to measure a patient's temperature. Such an embodiment would include using a temperature sensing device, on the distal end of a catheter for example, providing a faster temperature sensor and a temperature more closely similar to the core temperature of a patient. [0010] EEPROM or battery-powered RAM, on-board the microprocessor or in an external device, can be used to store the date and time at which a microprocessor controlling the pump and also monitoring a temperature probe, read the pump's temperature. The microprocessor can correlate an electrically measurable parameter, such as a temperature-dependent resistance of a thermistor for example, to a real temperature. The pump's temperature history since manufacture and prior to implant into a patient can be stored in memory and subsequently read from memory thereby providing a complete history of the pump's temperature. Historical temperatures stored and read prior to installation might help insure that the pump will not fail due to having been frozen or fail because of exposure to abnormally high temperatures since manufacture, causing a possible electrical or mechanical failure. [0011] Pump temperature data values stored in memory can be read from the pump prior to installation using a direct-connect-programming link or through a RF programming link, which is commonly used to transfer data to and from implantable infusion pumps and described elsewhere in the literature. See e.g. U.S. Pat. No. 4,676,248, "Circuit for Controlling a Receiver in an Implanted Device" by Berntson. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 discloses a simplified block diagram of an implantable, software controlled infusion pump that also includes a built-in temperature sensor. [0013] FIG. 2 shows an alternate embodiment wherein a catheter includes a temperature sensor coupled to a pump, which might include an external controller. [0014] FIG. 3 shows a flow chart illustrating the steps to compensate drug delivery flow in an infusion pump. [0015] FIG. 4A shows a graph of an uncompensated flow rate of an implantable pump versus temperature. [0016] FIG. 4B shows a graph of a temperature compensation algorithm's programmed relationship between pump revolutions per hour for an implantable pump and temperature. [0017] FIG. 4C shows a graph of a temperature compensated flow rate of an implantable pump. [0018] FIG. 5A shows the temperature profile of an implantable pump over time. [0019] FIG. 5B shows the histogram output of the total time an implantable pump was exposed to various temperature ranges. [0020] FIG. 6 shows a flow chart depicting the steps needed to produce a histogram output of the total time an implantable pump was exposed to various temperature ranges. Continue reading about Method to sense temperature in an implantable pump... Full patent description for Method to sense temperature in an implantable pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method to sense temperature in an implantable pump patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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