Thoracic Fluid Monitoring via Cardiac-Gated Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current implantable cardiac stimulation devices lack an effective method to monitor changes in thoracic fluid content, which is crucial for managing congestive heart failure, as existing methods require additional circuitry and are not adapted for detecting fluid status changes.
Innovation Solution
A fluid status monitoring system that performs subthreshold impedance measurements gated with the cardiac cycle, averaging or low-pass filtering to remove cardiac noise, allowing for the detection of clinically relevant fluid content changes without adding complexity to the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intra-thoracic impedance measurements are performed at high sampling rates to detect fluid status changes, then measurement precision is improved, but device complexity increases due to additional circuitry requirements
Solution Approach 1:
The patent applies multi-functionality by enabling the existing lead impedance measurement circuitry to serve dual purposes: traditional lead integrity monitoring and new fluid status detection. The same hardware infrastructure (excitation pulses, impedance measurement circuitry, sampling circuits) is utilized for both functions, eliminating the need for separate dedicated circuitry for fluid monitoring while maintaining high measurement precision through adaptive sampling rates.
Solution Approach 2:
The patent implements dynamic sampling rates that adapt to physiological conditions. The sampling rate is adjusted based on cardiac cycle detection and respiratory patterns, allowing high precision measurements during optimal time windows without requiring continuously high sampling rates. This dynamic approach maintains measurement accuracy while reducing overall circuitry complexity and power consumption.
2Adaptability or versatility
If impedance measurements are sampled at rates asynchronous with heart rate to determine minute ventilation, then respiratory monitoring capability is improved, but reliability decreases due to cardiac noise interference
Solution Approach 1:
The patent employs periodic action by synchronizing impedance measurements with the cardiac cycle. Excitation pulses are delivered at specific intervals during the cardiac cycle (during the refractory period) to avoid interference with cardiac activity. This periodic sampling strategy allows respiratory monitoring capability while maintaining measurement reliability by eliminating cardiac noise interference through precise timing of measurements relative to heartbeats.
Solution Approach 2:
The patent implements feedback mechanisms where the device continuously monitors cardiac rhythm and adjusts sampling timing accordingly. The system uses detected cardiac events to trigger impedance measurements at optimal moments, creating a closed-loop system that maintains measurement accuracy despite varying heart rates and respiratory patterns. This feedback approach ensures reliable fluid status detection while preserving respiratory monitoring versatility.
3Ease of operation
If monophasic excitation pulses are used for lead impedance measurements, then ease of operation is improved, but measurement precision deteriorates for fluid status detection
Solution Approach 1:
The patent applies parameter changes by modifying the excitation pulse characteristics adaptively. While monophasic pulses remain the default for simplicity, the system can switch to biphasic or other pulse configurations based on measurement requirements. This parameter flexibility allows the device to maintain ease of operation for routine lead monitoring while achieving enhanced measurement precision for fluid status detection when needed, by adjusting pulse parameters to optimize signal quality and reduce artifacts.
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
Enables early detection of pulmonary congestion and over-diuresis in CHF patients, reducing hospitalizations by providing a non-invasive, efficient means to monitor thoracic fluid status through impedance measurements integrated into existing ICD systems.
Implementation Method 1
impedance measuring circuitry for performing subthreshold impedance measurements
Data Source
AI summary
A fluid status monitoring system for use in implantable cardiac stimulation or monitoring devices is provided for monitoring changes in thoracic fluid content. A fluid status monitor includes excitation pulse generating and control circuitry, and voltage and current measurement and control circuitry for performing a series of cardiac-gated, intra-thoracic impedance measurements. The cardiac-gated measurements are filtered or time-averaged to provide a fluid status impedance value, with respiratory noise removed. Based on comparative analysis of the fluid status impedance value, a clinically relevant trend in fluid status may be tentatively diagnosed and a fluid status response provided. Cross-check intra-thoracic impedance measurements performed using the same or a different excitation pathway and a different measurement pathway than the primary intra-thoracic impedance measurement configuration may be used to verify a tentative diagnosis.