Blood Circuit Temperature Estimation Using Variable Flow Rates
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Solution Overview
Problem
Existing extracorporeal blood treatment systems face challenges in accurately measuring and controlling patient core temperature due to heat transfer variations along the blood circuit, particularly when using remote temperature sensors, as the heat transfer conditions are difficult to determine accurately due to manufacturing variability and environmental changes.
Innovation Solution
A method that involves measuring blood temperature at multiple flow rates and using thermal models to calculate the inlet temperature, employing techniques such as linear extrapolation, log mean temperature difference, and iterative refinement to compensate for heat transfer changes, allowing for accurate estimation of core temperature despite varying environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a remote temperature sensor is used to measure blood temperature in the blood circuit, then the measurement location flexibility is improved, but the temperature measurement precision deteriorates due to heat transfer variations along the circuit
Solution Approach 1:
The system changes the flow rate parameter of blood through the circuit to create different thermal conditions. By measuring temperature at multiple flow rates and using thermal models to calculate the inlet temperature, the system compensates for heat transfer losses in the circuit and retrieves accurate core temperature information despite using a remote sensor.
2Productivity
If the blood flow rate is increased to improve treatment efficiency, then the productivity is improved, but the temperature measurement accuracy deteriorates due to reduced heat transfer time
Solution Approach 1:
The system periodically varies the blood flow rate through the circuit, measuring temperature at different flow rates. This periodic change in flow conditions allows the system to gather multiple data points that are then used with thermal models to calculate the accurate inlet temperature, enabling precise measurement regardless of the actual treatment flow rate.
3Measurement precision
If multiple temperature measurements at different flow rates are taken to improve temperature calculation accuracy, then the temperature estimation precision is improved, but the measurement time increases
Solution Approach 1:
The system performs preliminary temperature measurements at different flow rates to establish thermal characteristics of the circuit. These preliminary data collection steps enable the development of accurate thermal models that can then rapidly calculate inlet temperature without requiring continuous multi-rate measurements during actual treatment, thus sacrificing time only during initial calibration.
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
This approach enables precise core temperature estimation and control, even in scenarios with variable heat transfer conditions, improving patient temperature management during extracorporeal blood treatments.
Implementation Method 1
a temperature sensor to measure a temperature of blood flowing through an attached blood circuit
Implementation Method 2
heat transfer between the blood and the external environment of the blood circuit
Implementation Method 3
imprecise values for heat transfer coefficients which are influenced by external forced convection
Implementation Method 4
the heat transfer rate is the same for two flow rate conditions. This gives two unknowns (the heat transfer rate) and two equations allowing the inlet temperature to be calculated
Data Source
Figure 1~3A
Figure 3B~3C
Figure 3D~3E
AI summary
A core temperature measurement may be made by varying the heat transfer dynamics of a blood circuit and fitting parameters of a blood circuit heat transfer configuration to measurements under the varied conditions. Then the input temperature of the patient core can be extracted from the model and a current temperature measurement remote from the patient core and optionally other measurements such as blood flow rate.