Circuit Compliance Compensated Volume Control in Respiratory Ventilators
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Solution Overview
Problem
Current respiratory ventilation systems struggle to accurately deliver tidal volume to patients, especially neonates, due to inadequate circuit compliance compensation, leading to gas trapping and auto PEEP, and are not responsive to changes in airway resistance and lung compliance.
Innovation Solution
A system and method for circuit compliance compensated volume control using a flow regulated feedback servo control loop, volume delivery controller, and patient volume observer, which estimates patient volume based on circuit compliance and measured net volume, maintaining a constant I:E ratio and adjusting inspiratory flow to prevent gas trapping and auto PEEP.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an estimate of patient circuit volume is directly added to set tidal volume by extending inspiratory time with specific peak flow, then patient circuit compliance is compensated, but the ability of the patient to exhale delivered tidal volume is impacted, resulting in gas trapping and auto PEEP
Solution Approach 1:
The system dynamically adjusts the inspiratory time extension based on real-time detection of patient breath initiation. When patient inspiration is detected, the system modifies the inspiratory time extension to prevent gas trapping, making the compliance compensation adaptive rather than fixed. This resolves the contradiction by making the volume compensation dynamic and responsive to actual patient needs.
Solution Approach 2:
The system uses feedback from patient breath detection to modulate the compliance compensation mechanism. By detecting when the patient initiates a breath, the system adjusts the inspiratory time extension in real-time, preventing gas trapping while maintaining accurate tidal volume delivery. This feedback loop eliminates the harmful effects of fixed compensation algorithms.
2Measurement precision
If an estimate of patient circuit volume is added to set tidal volume by increasing preset peak inspiratory flow, then patient circuit compliance is compensated, but average peak airway pressure increases causing runaway condition on neonatal patient size
Solution Approach 1:
The system dynamically selects between different compensation algorithms based on detected patient size category. For neonatal patients, it uses an algorithm that prevents runaway pressure conditions, while for adult patients, it may use the peak flow increment method. This dynamic adaptation resolves the contradiction by matching the compensation strategy to patient-specific requirements.
Solution Approach 2:
The system applies different compliance compensation strategies to different patient size categories (neonatal, pediatric, adult). Each patient category receives a customized compensation algorithm appropriate to their specific physiological characteristics, preventing the runaway pressure condition in neonates while maintaining effective compensation in adults.
3Measurement precision
If circuit compliance compensation is applied using fixed algorithms, then tidal volume delivery is improved, but the system is not responsive when changes in airway resistance and lung compliance occur
Solution Approach 1:
The system continuously monitors patient physiology and dynamically adjusts compensation parameters in real-time. When changes in airway resistance or lung compliance are detected, the system adapts the inspiratory time extension and peak flow adjustments accordingly, maintaining accurate tidal volume delivery despite physiological changes.
Solution Approach 2:
The system uses continuous feedback from breath detection and physiological monitoring to adjust compliance compensation parameters. This feedback mechanism enables the system to respond to changes in airway resistance and lung compliance, maintaining optimal tidal volume delivery across varying physiological conditions.
Data Source
AI summary
A system and a method for circuit compliance compensated volume control (30) in a patient respiratory ventilation system having a flow regulated feedback servo control loop (40), a volume delivery controller (34), and a patient volume observer (33). In the flow regulated feedback servo control loop, an estimate of patient volume is used for feedback control, such that a tidal volume is achieved upon servo regulation, and the peak inspiratory flow is modulated based on volume error between the set tidal volume and the estimated patient volume. Thereby, a constant inspiratory time and a constant I:E ratio can be maintained. In the volume delivery control, the feedback volume error is normalized to a volume error percentage, and the gain of the controller is dynamically changed based on the volume error percentage, such that the controller effort can be minimized when the volume target is approached. The patient volume observer is operative to estimate the patient delivered volume based on the estimated circuit volume and the measured net delivered volume, while the measured net delivered volume includes effects of leaks and valve dynamics and is synchronously captured with true patient breathing.