Technological advancements in lung simulators translate to substantial improvements in functionality.

By Dana Hinesly

Breathing simulators have made an impressive evolution since the 1970s, when they were considered secondary items. In fact, one of the first test lungs was developed to serve primarily as an in-house tool aiding with the creation of the company’s primary offering: a CPR machine.

“The original test lungs were basically invented out of necessity and were initially more popular with the academic community than with industry,” says R. Mitchell Baldwin II, president, RM Baldwin Inc, Grand Rapids, Mich. Even when they eventually rolled onto the market as a stand-alone product, they were passive systems simulating the pulmonary compliance and airway resistance of a patient.

Often referred to as “conventional lung simulators,” these simple machines relied mainly on bellows and springs for compliance and airflow resistance, lacking the ability to make adjustments to the simulated parameters on a breath-by-breath basis. While effective, they tended to be more difficult to set up, with a limited number of adjustment options.

One undeniable impact of faster and more powerful computers infiltrating medical industries was an entirely new generation of ventilators. Technology helped the devices evolve from relatively simple machines primarily counted on to entirely take over a patient’s breathing into today’s complicated systems, which are designed with an emphasis on aided breathing. It was imperative for simulators to be able to keep up.

“As ventilators started to grow in numbers and in complexity, it became more and more apparent that a passive lung simulator wasn’t adequate,” Baldwin says. “At that point, it was clear that some type of breathing simulator was necessary for testing the functionality.”

Systems were created with the ability to measure pressure, volume, and flow and then use those measurements in a mathematical lung model, calculating the output required to drive the mechanical lung. The same data is also used for real-time waveform displays and can be recorded for further analysis and reports.

“All of the modes, such as synchronized intermittent mandatory volume (SIMV), intermittent mandatory volume (IMV), pressure support, volume support, ventilation—they’re all meant to assist a patient in breathing rather than just completely breathe for them,” Baldwin says. “In the mid 1990s, we started working on the development of actively breathing lung simulators.”

Simulator-Enhanced Training

This new generation of simulators comes with an array of uses. As with any medical training program, respiratory therapists are eager to gain the knowledge necessary to do their jobs without putting patients at risk. It is critical that RT students have access to a realistic clinical situation in a regulated, nonclinical classroom setting. Modern lung simulators are sophisticated enough to make this possible, helping instructors demonstrate how a device responds to a particular set of patient parameters.

“It provides the ability to duplicate the functionality of a human lung and have those things be repeatable so you can teach in a controlled environment,” explains Maureen Oostendorp, marketing manager, Michigan Instruments, Grand Rapids, Mich.

Of course, when it comes to saving lives, nothing beats hands-on experience. For many RTs, that experience is now being found in the “perfect”—albeit nonhuman—patient.

“The use of full-body simulators, certainly in medical schools, is becoming a very popular approach,” Baldwin says, explaining that such multi-system simulators mimic a complete range of physical and physiological processes. “They look like a patient and they talk, they bite, all sorts of things. They’re very sophisticated, complicated machines, which makes them valuable, but also makes them expensive.”

Though out of budgetary reach for many academic institutions, the reproducibility of specific scenarios offered by these systems makes it possible for students to be evaluated objectively.

“RTs and pulmonary function testing technicians will be required to have training with simulators once the standards committees integrate the requirements to use simulators as standard practice with the patient-testing equipment in the clinical lab environment,” says Aaron Dirks, design engineer at Hans Rudolph Inc, Kansas City, Mo.

Baldwin concurs. “There’s a rapidly growing trend toward using simulators for not just training medical students or practitioners, but also for assessing their skills,” he says, adding that in some areas, simulated-based scenarios are implemented for accreditation and licensing purposes, rather than using live patients. “There is some cost savings and increased objectivity when specific simulations can be run and people’s skills can be assessed quantitatively and documented.”

For the many facilities that still find these human simulators beyond their budget, it does not mean students come up short. Skills can be learned just as effectively on so-called “task trainers,” which use a simple test lung to train on one specific procedure, such as an endotracheal intubation or manual ventilation.

Put to the Test

Training RTs and others on how to use ventilators properly is just one area where breathing simulators are in play. By providing predictable patient scenarios, these systems meet the needs of respiratory care professionals in a variety of ways.

Certified breathing simulators are industry staples for ventilator manufacturers, which use them to validate the safety and performance of their equipment in accordance with international standards.

“Simulators provide a known set of parameters that can be used to repeatedly simulate a patient with particular characteristics,” Dirks says. “Often this is the only way to verify that a particular feature is working correctly, which makes it a critical component of quality control and product development.”

Once ventilators are in use with patients, the type of dependable replication a simulator provides helps with the ongoing maintenance and monitoring active systems require—a job that often becomes the responsibility of resident biomedical engineers.

“Biomeds have another set of features they’re looking for in a breathing simulator,” says Stefan Frembgen, president, IngMar Medical, Pittsburgh. “They need documentation the test was performed and the equipment was working properly.”

When troubleshooting and resolving issues with ventilators, biomedical engineers are generally more concerned with accountability, having no use for the “bells and whistles” desired by other users of the breathing simulators. More affordable machines exist to meet this need.

“If a respiratory therapist has a problem with a ventilator on the floor and the biomeds can’t recreate the problem, they can use the simulator to run trend testing,” Oostendorp says. Technicians will leave the machine to run for hours, if necessary, she says, to obtain an accurate idea of the ventilator’s performance.

In addition to regular maintenance and repairs, facilities must test ventilators to ensure they continue to meet the manufacturer’s published specifications.

“It’s very important to know what the compliance and resistance of your test lung are,” says Jerry Zion, marketing manager, Fluke Biomedical, Carson City, Nev. “The purpose is to understand how the ventilation delivery system—the ventilator itself—is performing. If you can’t measure that, how can you evaluate it? The answer is you really can’t.”

Beyond putting simulators to work in quality assurance testing training, lung simulators are used regularly by research and development departments, providing a reliable way to gauge proof of concept and functionality.

Many lung simulators are under development for very specific purposes. Examples include test lungs driven by recordings of actual patient breath patterns or designed to imitate the breath sounds of a person buried in a disaster site.

“We’re involved with creating individual simulators for people’s research needs or specific training requirements,” Baldwin says. “This type of detailed research and development application is becoming as diverse as you can imagine.”

Technology Leads the Way

As with any industry, rapid technological advancements translate to substantial improvements in functionality.

“The software allows instructors to easily establish different parameters for specific diseases,” Oostendorp explains. With a few keystrokes, simulators will present an entire symptom set, without the hassle of adjusting the machine to create individual symptoms. “The system also allows them to quickly and easily set up a variety of self-paced training tutorials.”

Advancements in simulators are also growing in response to the increased complexity and sophistication of ventilation modes.

“When you’re looking at critical care ventilators or anesthesia ventilators, they are all driven by complicated technology that cannot be tested with simple pressure gauges and flow meters,” Baldwin says. This increased complexity demands simulators with the ability to closely and accurately simulate the patient parameters being measured.

Something for Everyone

New technology has produced a variety of available systems ensuring that facilities—whether they are involved in development or training—can find the system with just the right features to meet their needs.

One relatively new innovation in breathing simulators meets the needs of anesthesiologists looking to measure the amounts of oxygen and carbon dioxide passed with each “breath” the machine takes.

“More recently, some complex systems have been developed to simulate gas exchange and better mimic respiration,” Dirks says. These pricey devices adjust the composition of exhaled gases based on the metabolic model and inhalation parameters.

“The system is monitoring the flows and volumes and pressures in the airway as the volumes of gas are delivered by the ventilator,” Zion adds.

On the Horizon

“Because of the aging population and other factors, there’s a growing need to train more respiratory therapists. Though it’s still considered a niche area, there has been more interest lately,” Oostendorp says. “The training programs are full, which means they’re always looking for creative ways to get more students hands-on practice with the different techniques used in respiratory therapy.”

As competition grows, some feel that industry standards will need to adapt quickly or risk being outdated.

“Many standards do not take advantage of the improved technology in simulators,” Dirks says. “The standards organizations should encourage more quality control to make sure that the devices being used are working properly and giving reliable results. Without good measurements, a doctor may not be able to make a correct diagnosis.”

Frembgen also hopes the industry will continue to emphasize the important role breathing simulators play in training. He uses the analogy of pilot training.

“If you think about how physicians are educated today, it follows the traditional paradigm of a mentor/apprentice approach where clinicians are trained by watching someone until they are eventually given an opportunity to do it,” he says. “If pilots were trained the same way, not everyone would feel comfortable getting into an airline.”

Frembgen hopes that one day all training courses will provide students at all levels with a real-world, hands-on experience before leaving school.

“I would love to see respiratory training programs be more proactive in implementing simulation,” says Frembgen, who feels it is important to look at the use of simulators from a standpoint of curricula in respiratory care schools: How much should be incorporated? What should be used to determine the best uses of simulation?

“I don’t think there’s any question that simulation is going to become a bigger and bigger part of respiratory and anesthesia education as time goes on,” Baldwin says. “Really what has to happen is the simulations need to become more sophisticated but also of greater fidelity.”

Baldwin would like to see an increase in the incorporation of physiologic models—similar to the growing availability of gas exchange monitoring—to track what ventilators and other breathing systems are actually delivering.

“This is required in order to provide the optimal therapy for the patients themselves,” Baldwin explains. “Machines are being taught to do that, so we need to be able to test them objectively using similar mechanisms.”

Those in the industry also predict that ventilators and, subsequently, simulators themselves will continue to evolve.

“We’ll see more subtle improvements to take over more of the mundane tasks from the operator so they can focus on the actual treatment,” Frembgen predicts. Removing such duties from RTs’ “to do” lists frees them to develop strategies for improving patients and diagnostic and treatment methods. Simulators will be expected to match this functionality each step of the way.


Dana Hinesly is a contributing writer for RT.