Ventilation Sensor Rate Response Normalization
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Solution Overview
Problem
Existing implantable medical devices face challenges in accurately measuring minute ventilation due to variations in tidal volume, which can lead to inaccurate pacing therapy, as larger individuals with larger thoracic movements may exhibit different impedance differences than smaller individuals, and deep breaths can be misinterpreted as shallow breaths at different gain settings.
Innovation Solution
A cardiac rhythm management system that includes a signal processor to measure tidal volume and adjust the ventilation sensor rate response factor using information from the measured tidal volume, applying a normalization factor based on population-determined relationships and ventilation rate-dependent adjustments to compensate for filter non-ideality and tailor the pacing rate response for individual patients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance sensors are used to measure tidal volume, then ventilation rate can be monitored, but measurement precision deteriorates due to variations in chest size, sensor positioning, and current paths
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gain setting of the impedance sensor based on detected tidal volume levels. When shallow breaths are detected, the gain is increased to amplify the signal; when deep breaths are detected, the gain is decreased to prevent saturation. This adaptive parameter adjustment resolves the contradiction by maintaining measurement precision across varying physiological conditions while preserving reliable ventilation monitoring.
Solution Approach 2:
The patent implements dynamics by making the sensor gain setting dynamic rather than fixed. The system continuously monitors tidal volume and automatically adjusts the gain parameter in real-time based on the detected breath depth. This dynamic adaptation allows the system to handle both shallow and deep breaths accurately, resolving the measurement precision issue while maintaining overall monitoring reliability.
2Device complexity
If fixed gain settings are used in impedance sensors, then device complexity is reduced, but measurement precision deteriorates due to inability to distinguish deep breaths at low gain from shallow breaths at high gain
Solution Approach 1:
The patent applies self-service by enabling the impedance sensor system to automatically adjust its own gain setting based on the detected tidal volume characteristics. The system self-regulates by detecting whether breaths are shallow or deep and autonomously modifying the gain parameter accordingly, eliminating the need for manual configuration while maintaining high measurement precision across different breath depths.
Solution Approach 2:
The patent implements dynamics by transforming the static gain setting into a dynamic parameter that automatically adapts to varying breath conditions. The system transitions from a fixed configuration to a flexible, real-time adjustable setup, resolving the contradiction between device simplicity and measurement accuracy by using automated dynamic adjustment rather than complex manual configuration.
3Adaptability or versatility
If population-based rate response factors are used, then adaptability to different patients is improved, but measurement precision deteriorates due to individual variations in tidal volume and chest size
Solution Approach 1:
The patent applies preliminary action by implementing a calibration period during which the system collects tidal volume data from the specific patient before determining the personalized rate response factor. This preliminary data collection and analysis phase allows the system to establish patient-specific baseline characteristics, resolving the contradiction by preparing individualized parameters in advance that maintain both population-level adaptability and individual measurement precision.
Solution Approach 2:
The patent implements feedback by using the patient's actual tidal volume measurements to continuously refine and adjust the rate response factor. The system monitors the relationship between tidal volume changes and heart rate responses, then feeds this information back to optimize the personalized parameters. This feedback mechanism resolves the contradiction by maintaining adaptability to the patient population while achieving precision for the individual through continuous optimization.
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
This approach enables accurate normalization of minute ventilation rate responses, ensuring precise pacing therapy by accounting for individual variations in tidal volume and breathing patterns, thereby improving the reliability of heart rate adjustments based on metabolic needs.
Implementation Method 1
Minute ventilation can be conceptualized as the product of a patient's ventilation rate and the patient's tidal volume of air inhaled and exhaled during a particular breath. One or both of the patient's ventilation rate or tidal volume can be sensed using an impedance sensor that measures transthoracic impedance, which is modulated by the patient's breathing.
Data Source
AI summary
A cardiac rhythm management (CRM) device can extract ventilation information from thoracic impedance or other information, and adjust a delivery rate of the CRM therapy. A tidal volume of a patient is measured and used to adjust a ventilation rate response factor. The measured tidal volume can optionally be adjusted using a ventilation rate dependent adjustment factor. The ventilation rate response factor can also be adjusted using a maximum voluntary ventilation (MVV), an age predicted maximum heart rate, a resting heart rate, and a resting ventilation determined for the patient. In various examples, a global ventilation sensor rate response factor (for a population) can be programmed into the CRM device, and automatically tailored to be appropriate for a particular patient.