CSF Shunt Flow Measurement Pad with Control Thermistors
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Solution Overview
Problem
Existing methods for determining the flow status or flow rate of cerebrospinal fluid (CSF) in shunts implanted under the skin are either invasive or suffer from inaccuracies due to environmental variations and noise from thermistor signals.
Innovation Solution
A non-invasive apparatus using a pad with fast response thermistors aligned transversely over the shunt, coupled with a CSF analyzer, applies a temperature source to determine CSF flow rate by subtracting control thermistor signals from the shunt-aligned sensor signal, minimizing noise and environmental interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If thermistors are used to detect CSF flow, then flow detection capability is provided, but measurement precision deteriorates due to environmental changes and noise
Solution Approach 1:
The patent introduces control thermistors as intermediary elements that detect environmental temperature changes and noise. These control thermistors serve as mediators between the environment and the shunt-aligned thermistor, allowing the system to distinguish between environmental fluctuations and actual CSF flow signals. The control thermistor signals are subtracted from the shunt-aligned thermistor signal to eliminate environmental interference.
Solution Approach 2:
The system implements feedback by continuously monitoring environmental temperature changes through control thermistors and using this information to correct the measurements from the shunt-aligned thermistor. The feedback mechanism involves subtracting the control thermistor signals from the shunt-aligned thermistor signal, creating a corrected measurement that compensates for environmental variations and improves measurement precision.
2Measurement precision
If multiple thermistors are arranged to detect flow, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent divides the measurement function into separate segments: shunt-aligned thermistors for detecting CSF flow and control thermistors for monitoring environmental conditions. This segmentation allows each thermistor to have a specific function, improving measurement precision while organizing the device complexity into manageable functional modules that can be processed independently.
3Measurement precision
If invasive methods are used to measure CSF flow, then measurement accuracy is improved, but ease of operation deteriorates
Solution Approach 1:
The pad with multiple thermistors acts as an intermediary non-invasive measurement device that captures CSF flow information through the skin without requiring direct access to the shunt. This intermediary approach maintains measurement accuracy by using multiple sensors and signal processing while significantly improving ease of operation and clinical convenience.
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 provides accurate, repeatable, and convenient measurement of CSF flow rate and status, reducing errors from environmental changes and improving the ease of use for clinicians.
Implementation Method 1
a plurality of thermistors mounted on a flexible substrate coupled to a rigid base. The assembly is placed on the skin over the implanted shunt and a portion of the fluid in the shunt is cooled upstream of the assembly. The thermistors detect the cooled portion of the fluid as it passes the thermistor assembly
Implementation Method 2
The output of the thermistor is applied to an analog-to-digital converter for processing by a computer to determine the flow rate of the shunt fluid
Implementation Method 3
placement of cooling means downstream of the thermistor. The downstream thermistor detects the cooled portion of the CSF fluid as it passes from the region of the cooling means
Data Source
AI summary
A method and device for testing for the presence, absence and/or rate of flow in a shunt tubing implanted under the skin by using a measurement pad having a plurality of temperature sensors, one of which is aligned with the shunt and the other sensors being symmetrically displaced on either side of the first temperature sensor in a direction transverse to the shunt tubing. These “outer” temperature sensors act as control temperature sensors. A temperature source, e.g., a cooling agent, positioned within an insulated enclosure, is then applied at a predetermined location on the measurement pad that is insulated from the temperature sensors. The movement of this temperature “pulse” is detected by the shunt-aligned temperature sensor via the shunt tubing as the CSF carries the temperature pulse while the control sensors detect the pulse via convection through the skin. The temperature data from these sensors are provided to a CSF analyzer that determines a CSF shunt flow status or flow rate.