Loopy bird lungs make them breathe better

Research shows that birds breathe more efficiently than humans because of the structure of their lungs – curved airways that enable one-way air flows.

The results, from a series of laboratory tests and simulations, appear in the journal Corporate Review Letters.

The study also identifies softer ways to pump filters and control flows in applications such as breathing apparatus.

“Unlike the air flowing deep in the branches of our lungs, which oscillates back and forth as we breathe in and out, the flow flows. one-sided movement in birds’ lungs even as they breathe and creep, ”explained Leif Ristroph, associate professor at New York University’s Courant Institute of Mathematical Sciences and lead author of the paper .

“This allows them to perform the most difficult and costly activity of any animal: they can fly, and can do so across whole oceans and continents and at elevations as high as Mount Everest, where the oxygen to thin math. ”

“The key is that birds’ lungs are made of curved airways – not just branches and tree-like structure of our lungs – and we have found that this leads to one-way or directed currents around the lungs. loops, ”said Ristroph. “This wind cools even the deep recesses of the lungs and brings in fresh air. ”

“Spherical chicken” shows how the air movements back and forth during breathing (blue arrows) and exhalation (red) lead to a one-way (purple) flow around the loop. (Credit: NYU, NJIT Applied Mathematics Laboratory)

The one-way airflow in bird breathing systems was discovered a hundred years ago. But what remained a mystery was an explanation of the aerodynamics behind this efficient respiratory system.

To investigate this, the researchers performed a series of bird-like experiments.

For the experiments, they built a water-filled piping – to reproduce airflow – and twisted the pipe to mimic the loop structure in a bird’s lungs – similar to the way highways are connected by ramps and ramps . The researchers mixed microparticles into the water, which allowed them to monitor the direction of water flow.

These experiments showed that breath-generated back-and-forth movements were converted to one-way currents around the loops.

“This is exactly what happens inside the lungs, but now we could see and measure – and thus understand – what was going on,” explained Ristroph, director of the Applied Mathematics Lab, where the tests were performed. “The way this plays out is that the network has loops and therefore junctions, which is a bit like ‘forks in the road’ where the streams have a choice of what route that should be taken. ”

The scientists then used computer simulations to reproduce the experimental results and gain a better understanding of the devices.

“Inertia tends to cause the currents to continue straight rather than to turn down a side street, which is blocked by vortex,” explained coauthor Anand Oza, associate professor at the Institute of Technology New Jersey. “This culminates in one-way flows and looping around loops due to the junctions being connected in the network.”

Ristroph identifies a number of possible engineering uses for these conclusions about bird lungs.

“Managing, controlling, and pumping liquids is a very common goal in many applications, from healthcare to chemical processing to fuel, lubrication, and refrigeration systems in all types of appliances. , ”He observes. “In all of these cases we need to pump filters in specific directions for specific purposes, and now we have learned from birds a completely new way to achieve this which we hope can be used in the technologies. us. “

The research was supported by the National Science Foundation and the Simons Foundation.

Source: NYU