Non-Invasive Ventilator Oxygen Mix Control via Flow Coupling Filters
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Solution Overview
Problem
Existing non-invasive ventilator systems using blowers and compressed oxygen gas effused downstream of the blower outlet face challenges in controlling pressure and oxygen mix due to dynamic mismatches between the blower and oxygen valve, leading to complex control algorithms and instability, particularly at high mix settings.
Innovation Solution
A method and system utilizing a pressure controller, blower flow controller, and oxygen flow controller, along with complimentary flow coupling filters, to generate and adjust flow trajectories for the blower and oxygen source, ensuring stable control of pressure and oxygen mix by partitioning actuator influence over different frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If oxygen is introduced on the downstream side of the blower, then both the blower and oxygen valve become shared prime movers affecting pressure, but the blower and valve are grossly mismatched dynamically causing control difficulty
Solution Approach 1:
The control algorithm is segmented into distinct functional blocks: an outer pressure control loop that sets total flow requirements, and an inner flow distribution loop that allocates flow between blower and oxygen valve based on desired FiO2. This segmentation decouples the control of total flow from oxygen concentration control, managing the complexity of having two shared prime movers.
Solution Approach 2:
Multiple feedback loops are implemented: pressure feedback from the manifold controls total flow, oxygen concentration feedback adjusts the split between blower and valve flows, and flow sensors provide feedback on actual delivered volumes. This multi-layered feedback system handles the dynamic mismatch between blower and valve by continuously adjusting their respective contributions.
2Speed
If the blower flow responds slowly compared to the valve, then the valve can overcome the blower causing flow reversal, but fast valve response creates instability
Solution Approach 1:
The controller calculates preliminary flow setpoints for both the blower and oxygen valve based on the desired total flow and target FiO2 before actuation. This preliminary coordination ensures that the fast-responding valve does not overshoot or cause reverse flow by acting independently, but rather in a pre-coordinated manner with the slower blower.
Solution Approach 2:
The control system dynamically adjusts the relative contributions of the blower and oxygen valve based on real-time conditions. During transient states, the controller limits valve flow to prevent it from overcoming the blower, while during steady states, it allows greater valve participation for precise FiO2 control. This dynamic adaptation manages the speed mismatch between components.
3Device complexity
If a single controller structure is used for different patient types and ventilation modes, then device complexity is reduced, but control precision may be compromised
Solution Approach 1:
A single unified controller structure is designed to handle multiple ventilation modes (pressure support, controlled ventilation, spontaneous breathing) and different patient types through programmable control algorithms. The same hardware platform executes mode-specific control strategies by adjusting control parameters and loop configurations, eliminating the need for multiple dedicated controllers while maintaining precision through software-based adaptability.
Data Source
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AI summary
A method for controlling oxygen mix for a single-limb non-invasive ventilator comprising a pressure controller, and both a blower and a pressurized oxygen source downstream of the blower, each comprising a controller and a flow valve controlling flow, comprising: (i) generating a flow trajectory; (ii) providing the generated flow trajectory to a pair of complimentary flow coupling filters comprising a blower flow coupling filter and an oxygen flow coupling filter; (iii) generating an output from each of the filters, comprising an input flow trajectory for the blower flow controller and an input flow trajectory for the oxygen flow controller; and (iv) adjusting, by the blower flow controller and/or oxygen flow controller based on the input flow trajectory, target pressure, and oxygen mix, the blower speed controller and/or the pressurized oxygen source proportional flow valve.