It’s no secret—mechanical systems move differently than biological systems particularly when it comes to inertia. This concept has a number of significant implications when working with a mechanical test lung.

During ventilation, the inertia of the lung chamber must first be overcome before it can start to expand. Prior to this point, any gas delivered to the lung has been delivered into a chamber with static compliance. Only when the lung chamber begins to move do we see the dynamic compliance changes that would be expected of a normal patient. This results in a sharp peak in pressure data taken at the beginning of inspiration as the lung chamber overcomes inertia and at the end of expiration as the chamber returns to rest. Static compliance compensation is rarely included in ventilators and other medical instruments since it does not represent a normal patient scenario.

Physical Symptoms of Inertia

The most common physical symptom of this problem occurs during the expiratory phase. When a test lung with considerable inertia returns to rest at the end of a breath it can cause a pressure “bounce” in the airway that is sometimes strong enough to trigger an assisted breath from an IMV/SIMV compatible machine. While the false peaks in the pressure wave are rarely large enough to trigger limit warnings in a ventilator, this second breath caused by the bounce can skew tests measuring rate parameters such as breath rate and minute volume.

How to Resolve Measuring Rate Parameters

While frustrating, this problem is not unsolvable. Some mechanical test lungs are equipped with counterbalances to help minimize the inertia of the lung chamber while advanced breath parsing in instrumentation allows knowledgeable users to eliminate most of the false peaks that come up in testing. Tests themselves are often adjusted to get rid of these inaccuracies.

Almost all modern ventilation tests call for a PEEP of at least 5 cmH2O which (while being representative of actual ventilation practices) helps to reduce the inertia of mechanical and biological lungs alike. Decreasing I:E ratio can also help as it allows for a more gradual progression between the breath phases.

If you have any questions regarding the role inertia plays in mechanical test lungs, feel free to contact Michigan Instruments anytime, we are here to help!

It is no secret that military spending has gone down since sequestration (and other spending cuts), and simulation was one of the areas to take a major hit from this. This has led to increased private simulation lab interest and funding.

I remember attending the International Meeting on Simulation in Healthcare at the San Diego Convention Center in 2012. The sounds of my automated ventilator were constantly drowned out by faux gunfire and helicopter blades. Half of the people that walked by my booth were in uniform. Mannequins sported ragged gashes, shrapnel and even face paint.

Fast forward to 2014 in Orlando, these curiosities were nowhere to be found. Instead many of the rubber cadavers wore hospital gowns. Plenty of grave injuries made themselves present, but they were along the lines of blocked airways and organ complications. The focus of this industry is changing. While military spending is down, private spending in the realm of simulation is still very high. Simulation labs are becoming a new standard in modern hospitals, and those on the cutting edge of this industry are always looking for a way to improve their users’ experience.

Private User Attractiveness

As this change occurs, companies are beginning to ask questions about what will make their devices more appealing to private users. Cost is clearly not an issue. In 2012, a very high-end lung simulator would have cost between 25,000 and 35,000 USD. Just last week, at a show in Paris, I was introduced to a new lung simulation system with a base price of 46,000 Euros—well over 60,000 USD at the time.

Key Factors in Increasing Private Lab Simulation Attention

So, if cost is not an issue, how do we tap into this growing wealth of enthusiasm for simulation equipment? I won’t claim to have all of the answers, but customers have repeatedly asked questions that lead me to believe that the key factors are:

1. Anthropomorphism—Simulation lab directors tend to want their hardware to look human. This helps users to relate to the procedures that they are performing and increases the learning experience.
2. Durability—No one wants to spend 60,000 dollars on a device that will not last. Some of the most marketable simulation devices that I have seen have boxy steel frames or rugged, built-in carts that make transportation safe and easy.
3. Availability of Support—It’s a lot easier to be confident buying a unit with a substantial guarantee, warranty, or support policy.
4. The Range of Use—Very few customers will buy an extravagant device to simulate a single condition. The most successful simulators have a wide range of both “normal” and “abnormal” settings.
5. Reputation—The industry talks. If one intubation simulator has been bought by the majority of the simulation labs in a given area, new simulation labs nearby are likely to purchase it. It is becoming more important than ever to maintain excellent relationships with customers, as both complaints and praise can be spread worldwide on popular media sites.

The industry is in a constant state of flux of change; at Michigan Instruments, we always keep our ear to the ground and function in a consistent state of improvement, ensuring quality products no matter what. Reach out to us anytime to learn more and see how we can best help you.

This is part 2 of our series focusing on assessing high-frequency oscillatory ventilation. Check out part one here.

Due to difficulties in assessing the outputs (from the patient’s perspective) of HFOV ventilators, many analysts have resorted to monitoring pressure outputs. The theory is that so long as an adequate FIO2 (fraction of inspired oxygen) reaches the patient and the pressures remain safe, the ventilation is a success. Unfortunately, this method does little to help us understand HFOV on a deeper level, and without this understanding, it is difficult to know how the science and practice of modern ventilation will progress in the future.

Why is it important to understand volume and flow parameters?

Measuring ventilated volume is a common way of fact-checking a ventilator. For the display on a ventilator to show an accurate delivered volume the vast majority of the unit’s internal systems must be working properly. Flow, similarly, can offer insight into what might be going wrong with one of these ventilators, should it malfunction or require calibration. These parameters are sometimes overlooked in testing as the ventilator itself will display variations of them. Other variables make themselves in apparent when the problem of calibration is approached scientifically. Compressible volume in the airway and lungs can damage the accuracy of calculations performed by the ventilator, and without the ability to control airway resistance and lung compliance to a known value outputs are not always consistent.

The patient’s perspective.

Changes in flow and volume must be explored from the perspective of the patient as a way to understand, calibrate, and tweak ventilators. This sort of testing, however, requires a new type of test lung device capable of measuring flows, volumes, and pressures at different points throughout the respiratory system of a simulated patient.

We’ll get into test lung devices in part three. In the meantime, if you have any questions about the use of high-frequency oscillatory ventilation, don’t hesitate to contact Michigan Instruments anytime.