Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-11-22
2004-01-20
Hoang, Tu Ba (Department: 3742)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S030000
Reexamination Certificate
active
06681135
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to monitoring the internal temperature of an electronic device; and, more particularly, relates to a system and method for detecting and recording the temperature of an implantable medical device, such as a pacemaker or defibrillator, and using the temperature information to control the operation of the implantable medical device.
BACKGROUND OF THE INVENTION
Temperature measurements have been utilized in the past in conjunction with the control and operation of surgical medical tools. Such measurements are commonly used to determine when a treatment using heating energy is completed. For example, surgical tools are available to deliver energy to tissue at a point of incision to cause coagulation and prevent excessive bleeding. Such surgical tools may use temperature measurements taken from the treated tissue to determine when coagulation has been completed. A system of this nature is disclosed by U.S. Pat. No. 5,707,369 to Vaitekunas et al., which describes the use of temperature to determine when coagulation of tissue has occurred to a desired degree. Another similar example is provided by U.S. Pat. No. 5,496,312 to Klicek, which describes use of temperature measurements to regulate power supplied by a electrosurgical generator used to perform tissue desiccation. Tissue ablation systems also commonly use temperature measurements of adjacent tissue to control the amount of delivered ablation energy. Examples of these types of systems are provided by U.S. Pat. Nos. 5,743,903 and 5,906,614, both to Stern et al., and U.S. Pat. No. 5,810,802 to Panescu et al.
In addition to measuring temperature of adjacent body temperature, some medical systems use the temperature of internal circuitry to adjust system operation and performance. U.S. Pat. No. 5,897,576 to Olson et al. discloses an external defibrillation system that senses the temperature inside the power supply case of the device, and uses these measurements to adjust the operating parameters of the system, including capacitor charge time.
Implantable Medical Devices (IMDs) have also been provided that utilize temperature measurements to adjust therapy delivery. U.S. Pat. No. 4,905,697 to Heggs et al. describes a system that uses temperature sensed within the right ventricle of the heart to determine when a patient is exercising so that pacing rate may be elevated. Another similar system is disclosed in U.S. Pat. No. 4,782,836 to Alt et al. U.S. Pat. No. 5,814,087 to Renirie discloses a system that uses a drop in blood temperature to detect the onset of sleep so that pacing rate may be adjusted accordingly. Other pacemaker systems have been provided that use body temperature to perform capture detection. Such a system is disclosed in U.S. Pat. No. 5,336,244 to Weijand. Yet another example of the use of temperature within an IMD is provided by U.S. Pat. No. 5,089,019 to Grandjean, which discloses a system that uses intramuscular temperature to monitor performance of an implantable skeletal muscle powered cardiac assist system.
In addition to using temperature measurements for the purposes discussed in the foregoing paragraphs, a need exists to utilize temperature to regulate and control the system functions of an IMD that are not directly related to therapy delivery. One case in which temperature may be utilized in such a manner involves what is known as an Elective Replacement Indicator (ERI). An ERI is an indicator that is asserted when the battery power of an IMD has reached a predetermined low level. Upon assertion of this indicator, a battery replacement procedure is typically scheduled. This indicator may also be used to disable non-essential circuits so that overall power consumption decreases and battery power is conserved. The assertion of the ERI may further cause a pacing device to revert to a nominal pacing mode to further conserve power. One problem with the ERI is that sometimes this indicator may be erroneously set. This may occur prior to implant when an IMD is subjected to cold temperatures for a period of time. Cold temperatures cause the voltage of the IMD battery to drop. This initial voltage drop, or the subsequent voltage increase that occurs when the IMD returns to a warmer temperature, may cause the low-battery condition to be incorrectly detected. This, in turn, results in a latching of the ERI condition. In some circumstances, this may place the IMD in a low-battery state that can only be corrected using a manual override. To prevent this erroneous detection of a low-power condition, it is desirable to disable the ERI when the IMD reaches a predetermined low temperature.
Another situation in which temperature measurements may be used to control the logic functions of an IMD relates to a high-temperature quality control process known as “burn-in”. The burn-in process is used during manufacturing to stress the electrical components of the pacemaker by subjecting them to high temperatures and high operating voltages. The components that fail during burn-in are not used in products. Although most circuits are required to function at a burn-in temperature of 135° C., some circuits to such as CMOS bias generator mirror structures experience a significant shift in operating point that affects testing results. Additionally, some analog circuits must be provided with an increased current to operate properly at elevated temperatures. It is desirable to sense burn-in temperatures so that functions vulnerable to the high stress factors can be automatically disabled or appropriately compensated, and burn-in test results will not be erroneously affected by these circuits.
Yet another need for using temperature to control IMD operation involves the disabling of pacing and other functions of the IMD during the shelf-life of the device. This is useful for conserving battery power until the time of implant. This disabling function could be triggered, for example, by determining that the temperature of the IMD is not being maintained at a temperature that generally coincides with body temperature. Similarly, the detection of a temperature approximating body temperature could be used by the IMD to confirm the occurrence of implantation. These measurements could be used either alone, or in conjunction with other detection mechanisms such as body activity or impedance measurements taken between electrodes, to detect implantation.
Other uses of IMD temperature involve obtaining temperature measurements to control other treatment-related functions of the medical device. For example, the IMD temperature may be recorded to detect periods of extended exercise. Such extended periods of exercise will generally result in raising the internal body temperature. Upon detection of extended periods of exercise, the decay time constants can be adjusted. For example, following a prolonged period of exercise, it may be desirable to increase the time over which an elevated pacing rate is slowed to a normal pacing rate. It may also be useful to use temperature to set upper and lower rate limits. For example, after implantation is detected, a temperature above body temperature that is sustained for an extended period may be used to limit the upper pacing rate. Similarly, following implant, if a temperature below body temperature is detected for a substantial period to time as may occur during medical procedures such as an ice bath, the lower pacing rate may be limited so that the pacing rate does not drop too low.
Temperature measurements may also be used to compensate logical functions that are temperature sensitive. For example, some circuits such as Analog-to-Digital Converters require a reference voltage to operate properly. However, the reference voltage may drift with temperature changes, causing circuit operation that also varies with the temperature. A voltage compensation circuit may be provided to compensate for reference variations that are the result of temperature changes. Such a device may be programmably re-calibrated with data that reflects a current temperature, thereby m
Davis Timothy J.
Graden David W.
Reinke James D.
Wahlstrand John D.
Hoang Tu Ba
Medtronic Inc.
Soldner Michael C.
Wolde-Michael Girma
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