Non-Invasive Ventilator Airway Flow Estimation via Feedback Compensation
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Solution Overview
Problem
Non-invasive ventilator systems face challenges in accurately estimating patient airway flow and leak flow due to tubing resistance and compliance, which lead to inaccurate flow measurements at the ventilator, especially without a proximal flow sensor.
Innovation Solution
A method and system that utilize remote ventilator pressure and flow sensors, incorporating a feedback mechanism to minimize pressure errors and adjust for leaks by determining a gas flow leak factor on a breath-to-breath basis, with a proportional-integral compensator to stabilize the system and de-bias the airway flow estimate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If remote ventilator sensors are used to monitor flow, then the risk of occluding the airway with patient secretions is reduced, but the flow measurement accuracy deteriorates due to tubing resistance and compliance
Solution Approach 1:
The system uses a feedback mechanism where the estimated proximal pressure is compared with the measured proximal pressure, and the difference is used to adjust the estimated airway flow through a proportional-integral compensator. This closed-loop feedback resolves the measurement accuracy issue by continuously correcting errors introduced by tubing characteristics.
Solution Approach 2:
The patent introduces an intermediary mathematical model of the patient circuit that includes tubing resistance and compliance parameters. This model acts as a mediator to translate distal flow measurements into accurate proximal flow estimates, compensating for the tubing's effect on the measurement.
2Stability of the object's composition
If filtering is applied to pressure waveform measurements to account for resistance and compression, then the measurement stability is improved, but the measurement precision deteriorates due to noise amplification from differentiation
Solution Approach 1:
The proportional-integral compensator uses feedback to minimize the difference between measured and estimated proximal pressure, thereby reducing noise amplification while maintaining measurement stability. The integral component specifically addresses steady-state errors without requiring aggressive filtering.
Solution Approach 2:
The system changes the approach from directly differentiating noisy pressure signals to using a dynamic model with adjustable parameters (tubing resistance, compliance, leak resistance) that are optimized to match the actual patient circuit characteristics, thereby improving accuracy without excessive filtering.
3Measurement precision
If a proximal flow sensor is used to measure airway flow directly, then the measurement precision is improved, but the device complexity increases and the risk of airway occlusion rises
Solution Approach 1:
The patent extracts the flow measurement function from the proximal airway location and relocates it to the distal ventilator end, where sensing is simpler and safer. The system then uses mathematical modeling and feedback to recover the proximal flow information from the distal measurements, eliminating the need for a complex proximal flow sensor.
4Reliability
If leak is introduced in NIV to reduce end-tidal CO2 rebreathing, then the patient safety is improved, but the flow measurement accuracy deteriorates due to unknown leak flow loss
Solution Approach 1:
The system introduces a feedback mechanism that monitors the difference between measured and model-predicted proximal pressure, and uses this information to estimate and compensate for leak flow. This allows the system to maintain accurate flow measurements even in the presence of intentional leaks.
Solution Approach 2:
The patent replaces direct mechanical flow measurement (which would be inaccurate due to leaks) with a mathematical estimation approach using pressure measurements and circuit modeling. This substitution allows accurate flow estimation without being affected by leak-induced measurement errors.
Data Source
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AI summary
A method (800) for estimating patient airway flow in a non-invasive ventilator system includes: (i) determining (830) an estimated gas flow; (ii) determining (840) a proximal pressure error value; (iii) compensating (850) for the determined proximal pressure estimate error value; (iv) compensating (854) for an error in the estimated gas flow; (v) determining (856) an estimated gas flow leak; (vi) monitoring (860) on a breath to breath basis for a leak; (vii) determining (870) a gas flow leak factor; (viii) adjusting (880) the estimated gas flow leak; (ix) detecting (872) a bias on the airway flow estimate; (x) determining (874) that the system is within a quiescent state of a breath; (xi) de -biasing (976) the estimated gas flow to drive the bias to near zero; and (xii) suspending (878) breath to breath bias correction on an immediately subsequent breath.