Although creating human organ simulators sounds like an impossible feat, a local start-up is harnessing the latest in technology to create devices for the use of medical training and critical care education.
The Challenge
Creating a high-performance lung simulator that effectively emulates a diverse set of scenarios and ailments to assist medical students in training and education.
The Solution
Using Cyth’s off-the-shelf modular control system, Circaflex, and LabVIEW software to develop a lung simulator with capabilities to connect to a ventilator to achieve precision and responsiveness of a human-like standard.
The Cyth Process
A local start-up’s goal was to design and manufacture a lung simulator that could programmatically respond to different airway resistances and pressures. They approached us for help in creating a lung that could be fully responsive to a precise, human-like standard.
We partnered with the client to design a lung simulator for medical training and educational purposes, preparing doctors and medical staff for all scenarios that may occur during a medical procedure or surgery. The simulator can be sold and used as a standalone device or integrated with their previously created heart simulator, both of which are controlled by Circaflex, our off-the-shelf modular control system. The product resembles a real lung and can be hooked up to a ventilator, simulating real breaths taken. The lung then responds and the operator can programmatically increase airway resistance or lung compliance. This allows the medical staff to view plots on the ventilator as they study the lung or perform a surgery simulation, ensuring they are as prepared as possible before entering a real-world scenario.
The customer provided us with an equation to describe the normal function of a human lung when it is ventilating, and how the lung responds to air pressure when filled.
By using the equation to calculate the rate change of volume or the inflow of air, the lung simulator could be created to achieve human-like accuracy. By solving for the pressure and volume variables, our engineering team could program the motor that controls the lung to the correct speed. Our engineers decided to use a National Instruments’ 9651 RIO SOM, (System on Module), in conjunction with a Circaflex 304. The Circaflex 304 is a custom-built board designed to the exact dimensions of the RIO SOM and contains eight TTL lines, eight Analog Voltage Input channels, and one available expansion module slot.
To create the hardware for the lung, our team used a motor on a linear actuator and paired it with rubber bellows on the other end. When the motor was pulled back it would increase the volume, and when the actuator was pushed out, it would decrease the volume. This simulated the inhaling and exhaling that occurs within a human lung.
There are other lung simulators currently on the market, but to change the airway resistance the user needs to manually increase or decrease the mechanical iris. Other lung simulators contain multiple solenoids that require discrete airway paths to be picked to recover different resistance values. With Cyth’s lung simulator, airway resistance and lung compliance can be changed programmatically; there are no mechanical parts that attempt to change these values, it all happens in the software. Not only does it have a better more continuous range of values, but it’s easier to use at a lower manufacturing cost.
Overcoming the Obstacles
Our engineers decided to use the pressure transducer and motor encoder that came with the respective mechanical components. Because a stepper motor was being used, they introduced an RS232 module to communicate with it. However, the RS232 experienced a ten-millisecond delay when communicating with the motor. There was an additional five-millisecond delay from the pressure transducer, causing the encoder to read the written commands improperly. Because the speed of the motor is dependent on the lung volume, these delays caused inaccurate volume readings. Although it was only delayed by tens of milliseconds, the device was still too slow to simulate a human lung.
To circumvent this issue, we removed the control board from the stepper motor and spliced it into TTL lines, bypassing the manufacturer’s hardware to have direct access to the step and direction wires. The RS232 module was then removed and replaced with our Circaflex Stepper Drive module. After completing these changes, the motor could now operate for a few nanoseconds. The pressure transducer was also replaced with a new one that could now operate within the desired one-millisecond delay range, and the encoder was replaced with a displacement measurement sensor provided by SICK. These adjustments increased the overall accuracy and enabled all hardware to be able to operate within a one-millisecond delay range, solving the issue of speed and making the lung simulator achieve lifelike accuracy.
Delivering the Outcome
Through customer collaboration, we were able to design a product that better trains and prepares medical staff. The lung can simulate an array of diseases such as emphysema, a collapsed lung, or even an asthma attack. By creating a lung simulator that can be used in conjunction with their previously designed heart simulator, the client now has a turnkey system that accurately shows how these two organs interact with each other when the human body is under duress. Since the cardiovascular and pulmonary systems are very closely related, these two devices demonstrate to trainees how a patient’s lungs could be ventilated and how that affects blood oxygen levels, and in turn, the heart.
Whether our device is used in conjunction with the heart simulator or used stand-alone, the lung simulator has proven to be a groundbreaking design that performs with incredible accuracy and realism. We continue to partner with this client to provide better simulations and lifelike responses that surgeons and medical students alike can train with and learn from; ensuring that they’re prepared to perform at their best when operating on real patients.
Technical Specifications
• 1 x CompactRIO System on Module (sbRIO-9651), 667 MHz Dual-Core CPU, 512 MB DRAM, 512 MB Storage, Zynq-7020 FPGA
• 1 x Circaflex 304 (915-01414-02)
• 1 x Circaflex Stepper Driver Module (915-00304-01)
• 1 x Mass Flowmeter and Controller with Integral Display (FMA-A2321)
• 1 x Displacement Measurement Sensor, OD Mini (OD1-B100C50I14)
• 1 x SCN5 series, Dyadic's Mechatronics Cylinder
• 1 x Round Bellow with Cuff Ends