Oral-Nasal Cannula Segmentation for Independent CO2 and Flow Measurement
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Solution Overview
Problem
Existing oral-nasal cannula systems for breath flow measurement are unreliable due to false hypopnic event detection caused by cannula movement and open-mouth breathing, which can lead to inaccurate CO2 and breath flow readings, especially in patients with obstructive sleep apnea.
Innovation Solution
An oral-nasal cannula system with a CO2 sampling sub-system and a breath flow measurement sub-system that operate independently, featuring early separation of nasal and oral breath collection to prevent cross-interference, using separate prongs for CO2 and flow measurement, and a self-contained electronic pressure sensor to mitigate errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single oral-nasal cannula is used for both CO2 sampling and breath flow measurement, then device complexity is reduced, but measurement precision deteriorates due to cross-interference between the two measurement functions
Solution Approach 1:
The single cannula is segmented into functionally independent sub-systems: a CO2 sampling sub-system with separate prongs for nasal and oral breath collection, and a breath flow measurement sub-system with its own pressure sensor and flow path. This segmentation allows each sub-system to perform its measurement function independently without cross-interference, resolving the contradiction between device simplicity and measurement precision.
2Ease of operation
If pressure sensor technology is used for breath flow measurement, then ease of operation is improved, but reliability deteriorates due to false hypopnic event detection caused by cannula movement and open-mouth breathing
Solution Approach 1:
The cannula separates nasal and oral breath collection into distinct prongs with independent flow paths to the CO2 sensor and flow meter. This segmentation prevents false hypopnic events by ensuring that each measurement reflects actual breathing patterns rather than artifacts from mouth opening or cannula displacement, thereby improving reliability while maintaining ease of operation.
Solution Approach 2:
Separate flow paths act as intermediaries between the patient's breath and the measurement instruments. These dedicated channels isolate the pressure sensor and CO2 sensor from direct exposure to ambient air and cannula movement artifacts, allowing accurate detection of true breathing events while filtering out false signals.
3Ease of operation
If a flow meter is used to measure tidal volume changes, then ease of operation is improved, but measurement precision deteriorates due to false hypopnic events from mouth breathing and cannula movement
Solution Approach 1:
The cannula implements segmented collection paths where nasal breath and oral breath are captured through separate prongs and directed through dedicated flow channels. This segmentation ensures that the flow meter measures only the intended breath stream without contamination from mouth breathing or ambient air, thereby improving hypopnic event detection accuracy while maintaining operational simplicity.
Solution Approach 2:
Dedicated flow channels serve as intermediaries that isolate the flow meter measurement from sources of error such as mouth opening and cannula displacement. These intermediate pathways ensure that pressure changes detected by the flow meter accurately reflect true tidal volume changes rather than artifacts, resolving the contradiction between ease of use and measurement precision.
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 system provides accurate and independent measurements of CO2 and breath flow without cross-interference, improving diagnostic accuracy for sleep apnea and other respiratory conditions by minimizing false event detection and ambient air dilution.
Implementation Method 1
Since infrared light was found to be absorbed particularly well by CO2, capnographs usually measure infrared absorption in the breath gasses, which indicates the level of CO2 in these gasses.
Implementation Method 2
Pressure changes detected are proportional to flow, and hence evaluation of the changing pressure felt along the cannula provides a breath flow pattern relative to the patient flow dynamics.
Implementation Method 3
The thermistor is sensitive to the flow of air passing across it, which creates slight changes in its temperature.
Data Source
Figure 1A~1B
Figure 1C
Figure 2A~2B
AI summary
An oral-nasal cannula comprising at least one nasal breath inlet for carbon dioxide (CO2) sampling; and at least one nasal breath inlet for flow measurement, wherein said at least one nasal breath inlet for flow measurement is separated from said at least one nasal breath inlet for CO2 sampling, such that said cannula is configured to facilitate CO2 sampling and flow measurement essentially without cross-interference.