CIRCUIT FOR MEASURING MONOPOLAR AND BIPOLAR LEAD RESISTANCE FOR SPINAL CORD STIMULATOR AND DEEP BRAIN STIMULATOR
Publication Date: 2003-Jul-22
The IP.com Prior Art Database
AbstractA low-power circuit measures the impedance between the case and any electrode (a monopolar measurement), or the impedance between any two electrodes (a bipolar measurement) of an implantable neurostimulator, such as a spinal cord stimulation (SCS) device or a deep brain stimulation (DBS) device. Lead impedance information obtained using the circuit may be used by a clinician to assess lead integrity or quality of lead placement -- parameters that are critically important for correct or optimized operation of a SCS or DBS device.
AND DEEP BRAIN STIMULATOR
The present invention relates to implantable medical devices, and more particularly to a circuit that can be utilized in such implantable devices to measure monopolar and bipolar lead resistance. Representative implantable medical devices in which the present invention may be used include, e.g., a spinal cord stimulator (SCS), a deep brain stimulator (DBS), or other neurostimulator devices.
Being able to measure lead impedance for an implantable medical device has long been sought for as a tool for evaluating lead integrity, quality of lead placement, growth of fibrous tissue around the electrode, and the like. While prior art devices have had this capability, see e.g., U.S. Patent 5,603,726 incorporated herein by reference, such use has generally been in devices where power consumption of the implant was not critical, e.g., in a cochlear implant device where operating power has been provided from an external source through an inductive link. What is needed is a low-power technique for measuring lead resistance suitable for use in implant devices where power consumption is critical.
The present invention addresses the above and other needs by providing a low-power circuit that measures resistance between the case and any electrode (monopolar measurement) or the resistance between any two electrodes (bipolar measurement). Such circuit is preferably suitable for incorporation into an integrated circuit that may be included within the implant device, e.g., a SCS device or a DBS device. Lead impedance information obtained using the circuit of the present invention may advantageously be used by a clinician to assess lead integrity or quality of lead placement -- parameters that are critically important for correct or optimized operation of a SCS or DBS device.
The impedance measuring circuit of the present invention is capable of measuring the impedance between the case and any electrode or between any two electrodes. It provides a buffered, differential sampled voltage level that is directly proportional to the impedance between the two points being measured. The differential voltage can be digitized by an off-chip analog-to-digital converter (ADC), and the resulting digital code can then be used to compute the lead impedance (resistance). It should be noted that the terms “impedance” and “resistance” are used interchangeably throughout the description that follows.
FIG. 1 is a schematic diagram of the lead resistance measuring circuit of the present invention configured for a monopolar measurement. Thus, the circuit configuration of FIG. 1 measures the lead impedance between the case electrode and another electrode E1. The lead impedance is represented in FIG. 1 by load resistance RL. One side of RL is connected directly to the case electrode, identified as CASE in FIG. 1, whic...