Bioimpedance Sensor Lead for Hemodynamic Monitoring
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Solution Overview
Problem
Existing hemodynamic parameter measurement techniques for active implantable medical devices face challenges such as durability issues, high power consumption, and signal saturation due to local contact impedance variations, particularly in bioimpedance measurements for cardiac activity monitoring.
Innovation Solution
A novel bioimpedance sensor design with a single lead that integrates impedance measurement capabilities, using a tripolar electrode configuration with a shared reference electrode, allowing for controlled current injection and separate signal detection, thereby avoiding the impact of contact impedance variations and enabling accurate measurement of hemodynamic parameters without signal saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pressure sensor or accelerometer is used to measure hemodynamic parameters, then measurement capability is provided, but durability is reduced and power consumption increases
Solution Approach 1:
The patent replaces mechanical sensors (pressure sensors, accelerometers) with an electrical impedance measurement system. By measuring bioimpedance changes in the blood flow, the system derives hemodynamic parameters without mechanical components, thereby improving durability and reducing power consumption while maintaining measurement capability.
Solution Approach 2:
The patent changes the measurement parameter from mechanical pressure or acceleration to electrical impedance. By injecting a current through electrodes and measuring the resulting voltage, the system calculates impedance values that correlate with blood flow characteristics, providing an alternative measurement approach with different physical constraints.
2Measurement precision
If a dedicated multipolar lead is used for bioimpedance measurement, then measurement capability is provided, but device complexity increases
Solution Approach 1:
The patent makes the stimulation lead multi-functional by integrating both stimulation electrodes and impedance measurement electrodes into a single lead structure. The same lead that delivers neural stimulation also performs bioimpedance measurements, eliminating the need for separate dedicated measurement leads and reducing overall device complexity.
Solution Approach 2:
The patent combines the stimulation function and measurement function into a single integrated lead. By merging these two previously separate functions into one lead structure, the system reduces the number of components and simplifies the overall device architecture while maintaining both capabilities.
3Measurement precision
If a bipolar configuration is used for impedance measurement, then local impedance changes can be measured, but contact impedance variations cause signal saturation
Solution Approach 1:
The patent segments the measurement function into two distinct electrode pairs: one pair for current injection and another pair for voltage measurement. This segmentation allows the measurement circuit to exclude the contact impedance of the current-injecting electrodes from the measurement, preventing signal saturation while maintaining the ability to measure local impedance changes.
Solution Approach 2:
The patent introduces an intermediary measurement electrode pair that acts as a buffer between the current injection and the measurement circuit. This intermediary pair measures the voltage without being the site of current injection, thereby mediating the measurement process to avoid direct exposure to contact impedance variations that would cause saturation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides reliable and accurate hemodynamic parameter measurements, including blood pressure and cardiac activity, without affecting the detection circuitry, and allows for neurostimulation control based on bioimpedance data, enhancing the effectiveness of cardiac therapy and reducing the need for dedicated sensors.
Implementation Method 1
a first pair of electrodes for bioimpedance measurement connected to a current generator for circulating a current in a controlled manner into the blood vessel
Implementation Method 2
a second pair of electrodes for bioimpedance measurement connected to the input of an amplifying and processing circuit. The second pair of electrodes are configured to detect a signal from which said bioimpedance measurements can be extracted
Data Source
AI summary
An implantable device includes a lead, for example for neurostimulation of the vagus nerve. The lead includes a series of stimulation electrodes and a series of external electrodes for bioimpedance measurements on blood flow located in the same region, for example on the carotid artery. The device further includes means for separating into frequency bands the measured bioimpedance signal, the bands selected to reflect different respective activities such as vasomotor activity, hemodynamic activity, respiration, and cardiac rhythm activity.