A mechanical ventilator delivers oxygen-rich air to a patient's lungs via an endotracheal tube when the patient cannot breathe independently. The lungs are sensitive and complex organs, making it vital to provide air within intolerable pressure and volume limits, timed according to the required breaths per minute, and appropriately humidified and heated. The accurate modeling of mechanical ventilators is crucial for their safe and effective operation. Mistakes can result in inadequate ventilation and harm to the patient.
Challenges include mimicking airflow dynamics, pressure settings, and the complicated interactions between the ventilator and the patient. Addressing these challenges requires advanced simulation tools and expertise in both engineering and physiology.
Flownex: A Powerful Simulation Tool for Medical Systems
Flownex is a powerful simulation software for modeling complex fluid and thermal systems, utilizing the principles of mass, momentum, and energy conservation. It is widely used in industries for HVAC optimization, control system design, and industrial processes, making it ideal for mechanical ventilators. The software features an extensive component library and an intuitive interface, enabling engineers to develop detailed models without extensive programming skills. Flownex's advanced algorithms allow for accurate predictions of system behavior, ensuring ventilators operate safely and efficiently.
Furthermore, Flownex facilitates the creation of medical systems that involve fluid dynamics and thermal management, equipped with specialized tools for simulating lung components. Its comprehensive control library and visualization features assist in developing human-machine interfaces (HMIs), enhancing product design efficiency, and accelerating time to market. Prioritizing patient safety is essential in the design and control of ventilators. Flownex enables extensive testing to detect potential issues early and establish safety protocols. It also fine-tunes ventilator settings to improve patient outcomes by balancing oxygen and carbon dioxide levels, alleviating discomfort, and reducing the risk of lung injury.
Modeling and Controlling A Mechanical Ventilator in Flownex
Flownex features a sophisticated control library that seamlessly integrates with the Flownex flow network, allowing users to easily visualize control system results using the built-in visualization tools.
To begin modeling mechanical ventilators in Flownex, it's essential to define the system's components, including the air supply, control valves, sensors, and patient interface. Flownex's graphical interface facilitates the arrangement and connection of these components. The preliminary design for a mechanical ventilator and integration of the flow network, control model, and user interface to interact with the control and then the flow network are shown below.
1- Flow model for the mechanical ventilator
In the respiratory system, air must be delivered with precise timing and specific volume limits. The ventilator can be viewed as a pneumatic system, as shown in the flow network above. Flownex offers a library of predefined components, simplifying the selection and configuration of necessary parts. The flow network for the ventilator includes two tanks for oxygen and air, two valves to control the oxygen flow, a variable volume to simulate the lungs, and two control valves for inhalation and exhalation. The table below details the Flownex flow components used to model the respiratory system in a mechanical ventilator.
During inhalation, air flows from the tanks to the variable volume. During exhalation, air moves from the variable volume through the expiratory valve and exits to the atmosphere.
2- Control system
The control system regulates the inspiratory and expiratory valves. When the lung is breathing in, air flows from the tanks into the variable volume. When the lung is breathing out, air moves from the variable volume through the expiratory valve and is released into the atmosphere. Flownex controls offer a comprehensive library of control components, including both analog elements (like PID components) and digital elements, such as logic gates (AND, OR, etc.), switches, and timers. PIDs are proportional-integral-derivative controls, switches are used to compare different inputs, and counters are used to increment values.
In Flownex, we can implement various control modes to establish commonly used settings for ventilators. These control modes are based on the key parameters necessary for the correct operation of the ventilator. The parameters required to implement the control system for a mechanical ventilator in Flownex are:
- Breaths per minute (BPM)
- PEEP (positive end-expiratory pressure) refers to the lung pressure at the end of expiration. It is a critical parameter because if PEEP is too low, it can lead to alveolar collapse, resulting in inflammation and various medical complications. Additionally, Pmax represents the maximum pressure in the lungs after inspiration.
- TLC is total lung capacity
-
Vt is the tidal volume of the lung, representing the difference in volume between breaths.
-
Volume Control is a specific simulation mode executed in Intermittent Mandatory Ventilation (IMV), allowing the patient to breathe independently between cycles. This hybrid mode permits the patient can breathe on his/her own, and if the patient does not initiate a breath within the set time, the ventilator automatically assists.
These parameters are defined and used in the lung component, which is a compound component in the Flownex flow model (figure above). Using these parameters, we can export some important properties of the flow network: lung state, current pressure, etc.
To implement a control strategy in Flownex, the design engineer must ask the two what/how questions:
We use the control components and the above methodology to build two control models to implement the above control modes:
- Breaths per minute (BPM) and PEEP for controlling the opening and closing of the expiratory valve.
These tables outline the steps and specify the Flownex components necessary for designing the control models.
For instance, PID control is used to maintain precise pressure and flow rates by continuously adjusting the ventilator's settings based on the difference between desired and actual values.
- Flow Control to control inspiratory valve
Flownex also allows for the integration of control strategies. Use its control modules to implement feedback loops and adjust parameters dynamically based on real-time data. This step is crucial for ensuring that the ventilator responds correctly to changes in patient needs.
3- User Interfaces
Flownex offers visualization tools like sliding/track bars, various buttons, and also graphs to monitor and verify the proper working of the control system. The human-machine interface (HMI) can be developed within Flownex and integrated with the control flow model for the ventilator.
Heating and Humidifying the air
We need to control the air temperature and humidity as well to not further damage sensitive lung tissue. Flownex contains a humid air flow model that enables us to do relevant calculations and utilize a psychometric chart to visualize the process.
After setting up the main parts of the Flownex model for a mechanical ventilator, we need to input the necessary parameters for each component. This includes the physical dimensions, material properties, and operational conditions. After setting up the model, we can run simulations to analyze the system's performance under various conditions.
Ozen Engineering Expertise in Flownex
Ozen Engineering has good experience with Flownex for various applications, including mechanical ventilator modeling and control. Our specialists use the software to deliver precise solutions tailored to client needs. With expertise in both technical and clinical aspects, we ensure our models are accurate and practical. Our commitment to excellence makes us a reliable partner in advancing healthcare technology through simulation solutions.
Basics of Flownex Control for Industrial Control Systems: https://blog.ozeninc.com/resources/flownex-controllers-and-control-systems
Mechanical Ventilation Webinar: https://www.youtube.com/watch?v=SNRiKba3vks
Analyzing the Performance of Crude Oil Pipeline with Oil Temperature Fluctuations Using Flowne: https://blog.ozeninc.com/resources/analyzing-the-performance-of-crude-oil-pipeline-flow-using-flownex