Neurostimulation IPG Impedance Modeling for Safe Active Discharge
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Solution Overview
Problem
Existing implantable pulse generators (IPGs) for neurostimulation face challenges in accurately estimating patient-specific impedance and managing charge dissipation during magnetic resonance imaging (MRI) and electromagnetic interference (EMI), leading to potential side effects and therapy degradation.
Innovation Solution
The IPG employs a programmable amplitude current regulator that uses active discharge pulses with an exponentially decreasing current pattern to emulate passive discharge, maintaining a high impedance loop and minimizing unintended neural stimulation during MRI or EMI exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional passive discharge methods are used during MRI, then charge dissipation is achieved, but low-impedance loops are created causing unintended neural stimulation and side effects
Solution Approach 1:
The patent inverts the conventional discharge approach by using active discharge pulses that maintain high impedance rather than creating low-impedance loops. The IPG actively controls the discharge process through programmed current patterns, reversing the traditional passive discharge mechanism that caused harmful stimulation.
Solution Approach 2:
The patent changes the impedance parameter during discharge by using active current control to maintain high impedance states. The system dynamically adjusts discharge current parameters (exponentially decreasing current pattern) to achieve effective charge dissipation while preventing the low-impedance conditions that cause unintended neural stimulation during MRI.
2Object-affected harmful factors
If active discharge pulses with exponentially decreasing current pattern are used, then high impedance is maintained minimizing neural stimulation, but device complexity increases
Solution Approach 1:
The patent makes the current regulator multi-functional by programming it to perform both therapy delivery and active discharge functions. The same programmable amplitude current regulator used for neurostimulation therapy is repurposed to generate exponentially decreasing discharge current patterns, eliminating the need for separate discharge circuitry and reducing overall device complexity.
Solution Approach 2:
The patent recovers the discharged charge back into the system during the active discharge phase, rather than simply dissipating it. The exponentially decreasing current pattern allows the system to safely return charge to the patient's tissue in a controlled manner, maximizing the utility of the discharge process while maintaining high impedance safety.
3Measurement precision
If impedance measurements are taken during stimulation pulses, then patient-specific impedance estimation is improved, but measurement precision is affected by time-dependent voltage changes
Solution Approach 1:
The patent performs preliminary impedance modeling by capturing multiple voltage measurements during the stimulation pulse before the discharge phase. The system proactively collects voltage data at different time points during the constant current stimulation pulse to build a complete impedance model, preventing information loss that would occur if measurements were taken only after stimulation.
Solution Approach 2:
The patent uses feedback from multiple voltage measurements taken during the stimulation pulse to continuously update the impedance model. The system monitors voltage changes in real-time during the constant current delivery and uses this feedback to accurately estimate patient-specific impedance parameters, compensating for time-dependent variations in the electrical characteristics.
Data Source
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AI summary
In one embodiment, an implantable pulse generator (IPG) for providing a neurostimulation therapy, comprises: pulse generation circuitry and pulse delivery circuitry for controlling generation and delivery of electrical pulses to a patient using one or more electrodes of a stimulation lead; measurement circuitry for determining characteristics of one or more electrodes selected for delivery of electrical pulses; and a processor for controlling the IPG according to executable code; wherein the IPG is adapted to calculate values for an impedance model of the one or more selected electrodes using the determined plurality of voltage measurements and to adjust current levels for the exponentially decreasing current pattern based on the calculated values for the impedance model.