Bi-directional Flow Sensor Pneumatic Noise Reduction
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Solution Overview
Problem
Existing bi-directional flow sensors in mechanical ventilators face inaccuracies due to high velocity pressure jets from small diameter endotracheal tubes and pneumatic noise, leading to increased deadspace and re-breathing of CO2, especially in neonatal and pediatric patients, where precise flow measurements are critical.
Innovation Solution
A bi-directional flow sensor with a baffle and flow obstruction design that disperses the pressure jet and minimizes pneumatic noise, ensuring accurate pressure measurements by straightening non-axial flow and promoting uniform velocity profiles, reducing deadspace and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance between the endotracheal tube and flow sensor is increased to disperse the pressure jet, then measurement accuracy is improved, but deadspace increases causing CO2 re-breathing
Solution Approach 1:
The flow sensor is divided into distinct functional sections: a pressure jet dispersion section with gradually expanding walls to disperse the high velocity pressure jet, and a measurement section with pressure taps positioned where flow is uniform. This segmentation allows the pressure jet to be dispersed before measurement without requiring excessive distance, thus reducing deadspace while maintaining measurement accuracy.
Solution Approach 2:
The tapered dispersion section acts as an intermediary between the endotracheal tube and the measurement section. It gradually transforms the high velocity pressure jet into a uniform flow pattern, mediating the transition and enabling accurate measurement at a shorter distance than would otherwise be required.
2Volume of stationary object
If a flow sensor is placed close to the patient interface, then deadspace is reduced, but measurement accuracy deteriorates due to high velocity pressure jet impingement
Solution Approach 1:
The flow sensor incorporates a dispersion section with gradually expanding walls that separates the pressure jet reception area from the measurement area. This allows the sensor to be placed close to the patient interface while still providing accurate measurements by dispersing the pressure jet before it reaches the pressure taps.
Solution Approach 2:
The pressure jet dispersion is achieved by expanding the flow sensor walls in the radial dimension, creating a tapered geometry that disperses the pressure jet laterally before it reaches the measurement section. This dimensional change allows close placement while maintaining measurement accuracy.
3Ease of operation
If the flow sensor uses standard larger diameter fittings, then ease of connection is improved, but velocity pressure from the smaller endotracheal tube causes measurement errors
Solution Approach 1:
The flow sensor features locally differentiated geometry: a smaller diameter section that matches the endotracheal tube diameter for accurate velocity pressure measurement, and a larger diameter section for ease of connection to standard fittings. This local quality variation allows the sensor to maintain measurement accuracy while providing ease of connection.
Solution Approach 2:
The flow sensor is segmented into different diameter sections: a smaller diameter measurement section that interfaces with the endotracheal tube and provides accurate measurements, and a larger diameter connection section that interfaces with standard fittings. This segmentation resolves the contradiction between measurement accuracy and ease of connection.
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
The solution effectively reduces pneumatic noise to less than 0.1 LPM, allowing precise triggering of breathing cycles at 0.2 LPM flow rates, minimizing CO2 re-breathing, and providing accurate flow rate measurements for both inhalation and exhalation phases.
Implementation Method 1
Differential pressure detection is one of the more common techniques for measuring flow of a gas. Differential pressure flow sensors include a flow restrictor positioned within the flow of gas passing through the sensor to allow measurement of the pressure drop (i.e., the differential pressure) that occurs across the flow restrictor.
Implementation Method 2
A bi-directional flow sensor with a baffle and flow obstruction design that disperses the pressure jet and minimizes pneumatic noise, ensuring accurate pressure measurements by straightening non-axial flow and promoting uniform velocity profiles
Implementation Method 3
The solution effectively reduces pneumatic noise to less than 0.1 LPM, allowing precise triggering of breathing cycles at 0.2 LPM flow rates
Data Source
AI summary
A bi-directional flow sensor may be adapted for reducing pneumatic noise during pressure sensing with a flow passing through the flow sensor. The flow sensor may include a hollow, tubular member having a throat section disposed between a ventilator end and a patient end. A flow restrictor may be disposed in the throat section and may be adapted to measure differential pressure in the flow. A baffle may be mounted at the ventilator end and may be adapted to minimize non-axial flow at pressure taps located on opposing ends of the flow restrictor. The patient end may include a flow obstruction configured to promote uniform velocity across the flow at the pressure taps during exhalation flow from the patient end to the ventilator end. The flow sensor can minimize pneumatic noise to less than 0.1 LPM to allow accurate patient flow measurement and triggering of inhalation and exhalation phases at flow rates of 0.2 LPM.