Thermal Control Unit Step Response for Patient Temperature
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Solution Overview
Problem
Thermal control systems often overshoot target temperatures when rapidly heating or cooling patients, leading to oscillations in temperature and difficulty in maintaining a stable temperature range.
Innovation Solution
A thermal control unit with a controller that implements a step change in fluid temperature and monitors patient temperature slope to adjust control loops, using different sets of coefficients based on slope changes to minimize overshoot and maintain a tighter temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the thermal control system rapidly heats or cools the patient to reach target temperature quickly, then the heating/cooling speed is improved, but temperature overshoot increases
Solution Approach 1:
The control system dynamically adjusts the fluid temperature in two stages: initially applying a step change to achieve rapid heating/cooling, then transitioning to a slower adjustment phase near the target temperature to prevent overshoot. This dynamic control strategy resolves the contradiction by adapting the heating/cooling rate based on the current temperature state.
Solution Approach 2:
The controller preliminarily determines an intermediate target temperature that is closer to the patient's current temperature than the final target temperature. By first heating/cooling to this intermediate point and then making finer adjustments, the system avoids direct overshooting of the final target while maintaining relatively fast overall response.
2Loss of time
If the thermal control system uses aggressive control to reduce the time to reach target temperature, then the response time is improved, but temperature oscillations increase
Solution Approach 1:
The control system employs periodic monitoring of the patient's temperature and adjusts the fluid temperature in controlled cycles. The controller continuously monitors temperature readings and makes incremental adjustments, creating a rhythmic control pattern that prevents oscillations while maintaining efficient progress toward the target temperature.
Solution Approach 2:
The system uses feedback control by continuously monitoring the patient's temperature readings and adjusting the fluid temperature accordingly. The controller compares the current temperature with the target temperature and modifies the heating/cooling rate in real-time, preventing overshoot and oscillations while maintaining fast response.
3Adaptability or versatility
If the thermal control system maintains a wide temperature range to accommodate patient variability, then the adaptability is improved, but the temperature control precision deteriorates
Solution Approach 1:
The control system applies different control strategies to different temperature ranges. During the initial phase, it uses aggressive step changes for rapid temperature adjustment, while near the target temperature, it transitions to precise fine-tuning control. This localized control quality allows wide overall adaptability while maintaining high precision near the target.
Solution Approach 2:
The controller changes the control parameters dynamically based on the temperature state. It uses different proportional-integral-derivative (PID) coefficients or control gains depending on whether the patient is far from or close to the target temperature, enabling both wide adaptability and precise control at different stages.
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 effectively reduces temperature overshoot and maintains the patient's temperature within a tighter range of the target temperature by dynamically adjusting the control mechanisms in response to patient temperature changes.
Implementation Method 1
The heat exchanger adds or removes heat from the fluid circulating in the circulation channel
Implementation Method 2
The fluid temperature sensor senses a temperature of the circulating fluid
Implementation Method 3
The pump circulates fluid through the circulation channel from the fluid inlet to the fluid outlet and out of the fluid outlet
Data Source
AI summary
A thermal control unit for controlling a patient's temperature includes a fluid outlet for delivering temperature-controlled fluid to a patient, a pump, a heat exchanger, and a controller that automatically implements a step change in the temperature of the fluid delivered to the patient. The step change is implemented prior to the patient reaching a target patient temperature. In the moments after (and in some cases the moments before) the step change, the controller monitors the rate of change of patient's temperature to evaluate whether the patient will reach the target patient temperature without reversing the step change, and/or how long it will likely take for the patient to reach the target patient temperature without reversing the step change. The controller then determines whether to reverse the step change or to switch to another algorithm for controlling the fluid temperature.