Although creating human organ simulators sounds like an impossible feat, a local start-up is harnessing the latest technology to create devices for the use of medical training and critical care education. Having already developed a heart simulator, their next accomplishment would be a lung simulator that could programmatically respond to different airway resistances and pressures. Yet they needed help creating a lung that could be fully responsive to a precise, human-like standard.
Cyth partnered with the client to design a lung simulator for medical training and educational purposes, preparing doctors and medical staff to respond to different ailments that may occur during a surgery or medical procedure. The simulator can be sold and used as a standalone device or be integrated with their previously created heart simulator, both of which are controlled by Cyth’s off-the-shelf modular control system, Circaflex. The end product resembles a real lung and can be hooked up to a ventilator, simulating real breaths taken. The lung then responds like how you would expect a human lung to, and the operator is able to programmatically increase airway resistance or lung compliance. This allows the medical staff to view the plots on the ventilator as they study the lung or perform a surgery simulation, ensuring they are as prepared as possible before entering into a real surgery.
Client Request & Cyth’s Solution
The client knew they wanted to simulate a human lung that could be connected to a ventilator, allowing them to change airway resistance and lung compliance. The customer provided an equation that described how the human lung works when it is ventilating, and how the lung responds to the pressure of air that fills it.
By solving the equation to calculate the rate of change of volume, or the flow of air into the lung, the lung simulator could be created to human-like accuracy. By solving for the pressure and volume variables, the team could program the motor that controls the lung to the correct speed. Cyth engineers decided to use an National Instruments’ 9651 (RIO SOM) in conjunction with a Circaflex 304. The Circaflex 304 is a custom-built board designed to the exact dimensions as the RIO SOM and containing eight TTL lines, eight Analog Voltage Input channels, and one available expansion module slot.
To create the hardware for the lung, Cyth’s engineering team used a motor on a linear actuator and a 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 human lungs.
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 the lung simulator developed by Cyth, 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, continuous range of values, but it is easier to use and costs less to manufacture.
Cyth’s 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 a 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 solve the problem, the team removed the control board from the stepper motor and spliced in 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 Cyth’s Circaflex Stepper Drive module. After completing these changes, the motor could now operate on a few nanoseconds. The pressure transducer was also replaced with a new one that could operate at 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 now all hardware could operate within a one-millisecond delay range, solving the speed issue and making the lung simulator even more lifelike.
By collaborating with Cyth, the customer was able to design a product that generates better training and preparedness for medical staff. The lung has the ability to simulate different 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. Your cardiovascular system and pulmonary system are very closely related, and these two devices can demonstrate to medical staff how a patient’s lungs could be ventilated and how that will affect their blood oxygen levels, affecting the heart.
Whether the device is used in conjunction with the heart simulator or sold and used alone, the lung simulator is a groundbreaking design that performs with incredible accuracy and realism. Cyth continues to partner with this client to provide better simulations and more lifelike responses that surgeons and nurses can train with and learn from; ensuring that they perform at their best when operating on real people.
• 667 MHz Dual-Core CPU, 512 MB DRAM, 512 MB Storage, Zynq-7020 FPGA, CompactRIO System on Module (sbRIO-9651)
• Circaflex 304 (915-01414-02)
• Circaflex Stepper Driver Module (915-00304-01)
• Mass Flowmeter and Controller with Integral Display (FMA-A2321)
• Displacement measurement sensor, OD Mini (OD1-B100C50I14)
• SCN5 series, Dyadic's Mechatronics Cylinder
• Round Bellow with Cuff Ends