Circuit Compliance Compensation in Pressure-Regulated 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 compensation for patient circuit compliance, leading to inaccurate volume delivery and potential over-delivery, and are not robust against changes in airway resistance and lung compliance.
Innovation Solution
A system and method for circuit compliance compensated pressure-regulated volume control using a pressure-regulated feedback servo control loop, patient volume observer, and dynamically updated circuit compliance pressure compensation factor, which estimates and adjusts peak airway pressure to maintain a constant I:E ratio and prevent gas trapping, utilizing existing sensors to account for leakage and actuator dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If circuit compliance compensation is implemented using direct volume addition algorithm, then volume delivery accuracy is improved for adults and pediatrics, but the system becomes unstable and may cause runaway conditions for neonatal patients due to high circuit compliance ratio
Solution Approach 1:
The patent changes the control parameter from direct volume addition to pressure-based compensation. By using peak airway pressure as the basis for calculating circuit compliance volume (Vcc = Ct × Ppeak) and implementing feedback control, the system achieves stable and accurate volume delivery across all patient sizes including neonates, avoiding the runaway conditions caused by direct volume addition algorithms.
2Measurement precision
If positive feedback of peak airway pressure is used to account for circuit volume, then circuit compliance compensation is achieved, but the system becomes non-robust in cases of high airway resistance due to gas compression effects
Solution Approach 1:
The patent implements a feedback control mechanism where the estimated patient volume (Vpatient = Vnet - Vcc) is continuously compared with the set tidal volume, and the peak airway pressure is adjusted based on the volume difference. This feedback approach ensures robust performance against changes in airway resistance and lung compliance, unlike open-loop positive feedback algorithms that fail under high resistance conditions.
3Device complexity
If circuit compliance compensation is not implemented, then the system operation is simple, but inaccurate volume delivery and inadequate flow are delivered to the patient
Solution Approach 1:
The patent enables the ventilator system to automatically measure and compensate for circuit compliance effects using its existing sensors and processors. The system self-calibrates by monitoring peak airway pressure and calculating the volume lost to circuit compliance, then adjusts the delivered volume accordingly, eliminating the need for manual clinician intervention while ensuring accurate volume delivery.
4Device complexity
If I:E ratio is not maintained constant during volume delivery, then the control algorithm is simpler, but gas trapping and auto PEEP occur
Solution Approach 1:
The patent dynamically adjusts the inspiratory time and peak airway pressure to maintain a constant I:E ratio throughout volume delivery. By making the inspiratory phase duration adaptive rather than fixed, the system prevents gas trapping and auto PEEP formation while keeping the control algorithm manageable through real-time parameter adjustment based on patient response.
Data Source
AI summary
A system and a method for circuit compliance compensated pressure control in a patient respiratory ventilation system, having a pressure regulated feedback servo control loop, a pressure-regulated volume controller, and a patient volume observer. The patient volume observer is operative to estimate a patient volume, that is, the volume actually delivered to the patient by accounting for volume deviation or loss caused by patient circuit leakage and valve dynamics. Based on the difference between the estimated patient volume and a set tidal volume, the pressure-regulated volume controller is operative to generate and update a circuit compliance pressure compensation factor. The pressure regulated feedback servo control loop is operative to modulate the peak airway pressure based on the circuit compliance pressure compensation factor, so as to achieve the set tidal volume while maintaining a constant inspiratory time and a constant I:E ratio.