Sensorless Blood Flow Estimation in Ventricle Assist Devices
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Solution Overview
Problem
Current ventricle assist devices (VADs) face challenges in accurately estimating blood flow rates due to variable blood viscosity, which affects the accuracy of pump flow and pressure head estimates, especially without supplemental sensors, leading to inadequate clinical data for patient monitoring.
Innovation Solution
A method is introduced where the VAD briefly interrupts power to its impeller, allowing for the estimation of blood viscosity by measuring the rotational speed decay rate, which is then used to calculate steady-state and transient blood flow rates, enabling precise control of the pump's rotational speed and power application based on viscosity and inertia corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard pump performance curves are used for flow estimation, then the device complexity is reduced, but the measurement precision deteriorates due to variable blood viscosity
Solution Approach 1:
The patent replaces mechanical flow sensors and pressure sensors with an electrical measurement system. By measuring the electrical current drawn by the motor and using pump performance curves, the system estimates flow rate without physical sensors in the blood path, thus maintaining low device complexity while improving measurement precision through electrical measurements.
Solution Approach 2:
The patent changes the measurement parameter from direct mechanical flow measurement to electrical current measurement. By monitoring motor current and correlating it with flow rate through performance curves, the system achieves accurate flow estimation without the complexity of mechanical sensors, addressing the contradiction between simplicity and precision.
2Measurement precision
If differential pressure sensors are added to improve flow estimation accuracy, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent substitutes mechanical pressure sensors with electrical current sensing. By measuring the electrical parameters (current, voltage, power) of the motor driving the impeller and using these with performance curves, the system achieves flow estimation accuracy comparable to or better than mechanical sensors, while avoiding the complexity of pressure transducers in the blood path.
Solution Approach 2:
The patent uses the motor's own electrical characteristics to provide flow measurement information. The motor's current draw serves as a proxy for flow rate, eliminating the need for separate measurement devices. This self-service approach maintains measurement precision while minimizing device complexity.
3Device complexity
If blood viscosity is not monitored, then the device complexity is reduced, but the measurement precision of flow rate deteriorates
Solution Approach 1:
The patent changes from attempting to directly measure blood viscosity to using electrical parameter measurements that inherently account for viscosity effects. By measuring motor current, power, and efficiency at different operating points and comparing with performance curves, the system indirectly captures viscosity variations without requiring direct viscosity measurement, thus maintaining low complexity while preserving accuracy.
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 provides accurate and continuous monitoring of blood flow and pressure head, allowing for optimal VAD operation and improved clinical data collection, including native heart function analysis without the need for additional sensors, thereby enhancing patient care.
Implementation Method 1
a blood pump having a rapidly rotating, electrically powered impeller for pumping of blood
Implementation Method 2
electrically powered impeller
Implementation Method 3
Such sensorless flow estimation can be determined through sensing of the current or the back EMF of the system
Implementation Method 4
the pressure increase created by the pump
Data Source
AI summary
A method of estimating the blood flow rate of a heart ventricle assist device which is positioned externally of, or implanted in, a patient. The assist device comprises a blood pump having a rapidly rotating, electrically powered impeller, and comprises briefly interrupting power to the impeller to cause its rotation to slow. From this, blood viscosity can be estimated, which viscosity is used to obtain real time, estimated blood flow rates and pressure heads. Apparatus for accomplishing this is disclosed.