Amorphous Fluoroplastic pCO2 Sensor with U-Shaped Tissue Deflector
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Solution Overview
Problem
Existing sensors for measuring partial pressure of carbon dioxide (pCO2) in tissue face challenges such as interference from low molecular weight acids in saliva and the need for precise pressure application to avoid disturbing microcapillary blood flow, particularly in oral mucosal tissue.
Innovation Solution
A carbon dioxide sensor system featuring a membrane body made of amorphous fluoroplastic, housed within a C-shaped sensor cover, with a sensor placement device that uses a U-shaped deflecting surface to position the sensor against buccal tissue without excessive pressure, ensuring 40-50% contact and shielding from end-tidal carbon dioxide, while using a ratcheting element to adjust for varying tissue thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If silicone membranes are used for pCO2 measurement, then rapid gas transport is achieved, but carboxylic acids in saliva pass through and interfere with measurements
Solution Approach 1:
The patent uses a composite membrane structure consisting of a silicone rubber layer and a polyacrylonitrile (PAN) layer. The silicone rubber provides rapid CO2 transport, while the PAN layer acts as a selective barrier that blocks carboxylic acids like acetic acid from passing through. This composite structure resolves the contradiction by combining materials with complementary properties - one optimized for gas permeability and another for acid rejection.
2Reliability
If pressure is applied to ensure sensor contact with tissue, then measurement reliability is improved, but microcapillary blood flow may be occluded causing measurement errors and tissue damage
Solution Approach 1:
The patent employs a compliant membrane structure that can deform elastically in response to applied pressure. When pressure is applied to ensure sensor contact with the tissue, the membrane deflects and distributes the force over a larger area, reducing peak pressure below the threshold that would occlude microcapillaries (typically <32 mmHg). This dynamic parameter adjustment allows the system to maintain reliable contact while avoiding harmful pressure levels.
3Measurement precision
If the sensor is isolated from ambient air to measure tissue pCO2, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent uses a thin, flexible membrane as both the sensing element and the isolation barrier. This single component simultaneously provides the sensing function (allowing CO2 diffusion) and the isolation function (blocking ambient air). The membrane's flexibility allows it to conform to tissue surfaces while maintaining the sealed environment necessary for accurate tissue pCO2 measurement, thereby achieving isolation without significant increase in device complexity.
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 measures pCO2 in tissue with minimal interference from saliva acids and maintains accurate readings by ensuring proper tissue contact without disrupting blood flow, providing reliable data for assessing hypoperfusion and preventing tissue damage.
Implementation Method 1
a membrane body made of amorphous fluoroplastic... allowing for the rapid transmission of carbon dioxide while preventing the transmission of low molecular weight acids found in the saliva
Implementation Method 2
a sensor placement device that is designed to hold and position the sensor against tissue... uses a U-shaped deflecting surface to position the sensor against buccal tissue without excessive pressure, ensuring 40-50% contact
Implementation Method 3
measuring the partial pressure of carbon dioxide (pCO2) in tissue... Carbon dioxide production, which is associated with metabolism, continues in tissues even during conditions of low blood flow. The concentration of carbon dioxide builds-up in tissues experiencing low blood flow
Data Source
AI summary
A physiologic sensor for measuring the partial pressure of carbon dioxide is provided. The sensor includes a generally C-shaped in cross-section sensor cover, the sensor cover defining an opening on an underside thereof; a membrane body housed within the opening, the membrane comprising an amorphous fluoroplastic, the membrane including a first end and a second end and defines a chamber therewithin; a sensor body for coupling the membrane to the sensor cover; two or more electrodes positioned within the membrane chamber; and a substantially electrolyte-free liquid contained within the membrane chamber and in contact with the two or more electrodes.