Lungs: "Liquid ventilation is still not sufficiently researched"

Interview with Dr. Katrin Bauer, Institute for Mechanics and Fluid Dynamics, TU Bergakademie Freiberg

All swimmers know the unpleasant feeling when you breathe in at the wrong time and then have water enter into your windpipe. At best, it immediately triggers the cough reflex, which is intended to keep the water away from the airways and prevent suffocation. However, liquid in the lungs can also save people - especially if it allows them to breathe again.

03/09/2015

Photo: Katrin Bauer

Dr. Katrin Bauer, © private

In this interview with MEDICA.de, Dr. Katrin Bauer talks about the concept of liquid ventilation with perfluorocarbon, its known and potential medical applications and how she intends to study oxygen transport in this liquid.

Dr. Bauer, how long has the concept of liquid ventilation been around?

Katrin Bauer: Liquid ventilation has been around since the end of the 1960s. It was first tested on animals. Researchers noticed that mice are able to breathe with the liquid perfluorocarbon. This gave way to the idea of gentle artificial ventilation for instance in patients with collapsed lungs. By using a liquid, their lungs could be reopened again in a gentler and better way than with gas ventilation.

What type of liquid is perfluorocarbon?

Bauer: Perfluorocarbon or PFC is very inert, meaning it does not undergo chemical reactions. What is particularly interesting is that it can dissolve oxygen. 100 ml of PFC will dissolve 50 ml of oxygen. Only 3 ml of oxygen will be dissolved in 100 ml of water. The liquid is also not being metabolized if it is in the body. It is simply exhaled via the lungs.

So there are no effects on the body?

Bauer: Of course, we still do not know the long-term effect of PFC weight on the body. The liquid is twice as dense as water. It could lead to side effects or displacements when it lies on top of other organs for an extended amount of time. However, this would not be due to chemical composition, but because of mechanical stress on tissue.

How does the oxygen supply work when lungs are filled with PFC?

Bauer: There are two methods of liquid ventilation. First, there is partial liquid ventilation. Here the lungs are filled with PFC up to a specific upper limit. This is the level at which the patient’s ventilation tube is located. Above it, the patient is hooked up to a normal mechanical ventilator. The gas exchange takes place via the interface between air and PFC. Due to high solubility, the oxygen from the air changes over to the liquid where it is being absorbed by the lung tissue. This process also works the other way around to where CO2 is released via this boundary.

The other method is total liquid ventilation. Here a ventilator and the lungs are filled with liquid, and oxygen is being added into circulation with each breath and CO2 discharged.
Photo: Silicon model of the lung in a bluely lit water tank

This lung model will be used in the simulations during the project; © TU Bergakademie Freiberg/Dr. Katrin Bauer

Are there already corresponding respirator systems?

Bauer: A research team at the Canadian Université de Sherbrooke has developed a device. It is presently in its sixth prototype generation, but is so far only being used in animal testing. Ventilation has also been done on humans, but only in studies and not in a routine clinical setting. However, these studies frequently only have a low number of cases and were actually aborted in part, because patient inclusion was not clearly regulated.

In your project, you focus on oxygen transport in liquid. How can we imagine the research for this?

Bauer: I use oxygen-sensitive particles that fluoresce when they are illuminated with laser light. Existing oxygen diminishes fluorescence intensity. The more oxygen there is, the higher the reduction. This is called "quenching" and it reveals the oxygen distribution: the more intense the glow is at a specific location, the less oxygen is available at this spot. For the analysis, I pour PFC with the oxygen-sensitive particles into a model. I can subsequently map how the particles move, where they are moving to and how bright they are glowing.

What type of model is this?

Bauer: This is a silicone model of the upper respiratory tract. This is not entirely realistic however, because the alveolar layer where the gas exchange takes place is missing. The upper respiratory tract is just my starting point, because we actually have no information on how oxygen and CO2 behave in there. However, for medical scientists it is very interesting to know what the oxygen distribution looks like in there.

Does your existing knowledge from gas ventilation actually help you with this?

Bauer: I can use this as a foundation, but there is an entirely different type of flow in the lungs. Air is approximately five times the viscosity of PFC. Normally, the flow in a gas-filled lung is laminar, that is to say, it is a directed motion and there is hardly any turbulence. With liquids, there is a turbulent flow in the lungs with strong swirling and strong cross-flow mixing. Until now, nobody has looked into this, because it cannot be realistically actualized. But I believe this can be done very soon.

In medicine, liquid ventilation is used experimentally in premature infants and patients with pulmonary symptoms. Why there?

Bauer: Premature infants are high-risk patients when it comes to collapsed lungs. When they are born too early, before week 36, they lack so-called surfactant. This surface-active agent prevents the agglutination of the pulmonary tissue. This in turn can lead to lung collapse. In these cases, you consider liquid ventilation. Lungs rarely collapse in adults.

What prevents medical science from being further ahead in this area?

Bauer: I believe it is currently the technical complexity of liquid ventilation combined with knowing from previous studies that patients have not benefitted more from it than they did from gas ventilation. There is simply not enough knowledge about it yet. As long as physicians are able to help patients with the field-tested gas ventilation, they are on the safe side and therefore have no reason to resort to an experimental procedure. The subject is still not sufficiently researched to where you could use liquid ventilation on a regular basis.
Foto: Timo Roth; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Timo Roth and translated from German by Elena O'Meara.
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