Ventilation of premature babies can be harmful. Inflating the lungs with excess pressure, as happens with ventilation, damages lung tissue, in contrast to natural breathing through stretching.
The lungs of premature babies are often not fully developed yet. This can cause their breathing to falter. ‘Artificial respiration is needed to save their lives,’ says Mareike Zinkprofessor of cell biophysics at the University of Leipzig.
But that ventilator can do damage. This is how the lung disease bronchopulmonary dysplasia (BPD) arise. The lung tissue changes irreversibly. A child with this condition has an increased risk of respiratory infections.
ALSO READ
The unsung heroes of science history
Zinc investigates with colleagues who also specialize in the care of premature babies, why and how artificial respiration causes damage to the lungs.
Breathe and ventilate
In their experiments, the researchers use lung tissue from preterm and adult rats. They mimic the effects of normal breathing and artificial respiration.
During a regular inhale, your diaphragm moves downward. This stretches your lungs and increases their volume. This creates a vacuum in your lungs so that you automatically suck in air and thus inhale. With artificial respiration, a device pumps air into your lungs, creating overpressure. That pressure forces your lungs to expand.
These two ways of getting air into the lungs each have a different effect on the lung tissue. The overpressure of ventilation causes the lung tissue to compress, while in normal breathing the movement of the diaphragm actually pulls on the tissue.
elastic breathing
“If lung tissue were fully elastic, it would behave the same during inflation as it did when stretched,” says Zink. ‘But the tissue is not elastic. It is viscoelastic. This means that the way you deform the material determines how it behaves. So pulling from the outside or pumping air in from the inside gives different results.’
To mimic breathing, the researchers stretched the lung tissue of preterm and adult rats. And they compressed the tissue, like they do with a ventilator. It turns out that the tissue behaves elastically when stretched – as with normal breathing. It springs back without changes in the molecular structure of the lung tissue.
This does not appear to apply to the tissue that is compressed when you pump air into it. The researchers saw that the expansion of the lungs depends on the frequency with which they ‘pump up’ the tissue. The faster they inflate and deflate it, the stiffer the material behaves.
This indicates that small changes are taking place in the lung tissue. Zink: ‘Small breaks occur on a molecular scale, which means that the molecular structure is damaged. And we don’t want that.’
Stiff lung tissue
The researchers also found that the lung tissue of preterm rats is stiffer than that of adult rats. So you need a higher air pressure to enlarge the lung. That’s also what doctors notice: it’s difficult, even with high pressure, to get the lungs to stretch. But you also don’t want to use too much pressure, because that can cause ruptures in the lungs.
“It would be best to avoid the need for ventilators,” Zink says. ‘We also know that from COVID-19 patients, where we see that ventilation can cause damage in the lungs. That is why doctors usually wait as long as possible and only ventilate if it is really necessary.’
A way to get air into the lungs without damaging the lung tissue does not yet exist. Everything is tried, such as ventilation with varying pressures and different speeds. But it is not yet clear what the best approach is. By further mapping the effects on tissue structure, the researchers hope to find an answer in the future.