Researchers identify ‘violent’ physical processes that cause wheezing

A team of engineers have identified the “violent” physical processes at work inside the lungs that cause wheezing, a condition that affects up to a quarter of the world’s population.

The researchers, at the University of Cambridge, used modeling and high-speed video techniques to show what causes wheezing and how to predict it. Their results could be used as the basis for a cheaper and faster diagnosis of lung disease that only requires a stethoscope and microphone.

A better understanding of the physical mechanism responsible for the production of wheezing sounds could provide a better causal link between symptoms and disease, and help improve diagnosis and treatment. The results are reported in the journal Royal Society Open Science.

At some point, most of us have experienced wheezing, a high-pitched hissing sound emitted while breathing. For most people, the phenomenon is temporary and is usually the result of a cold or mild allergic reaction. However, regular or chronic wheezing is often a symptom of more serious conditions, such as asthma, emphysema, chronic obstructive pulmonary disease (COPD), or certain cancers.

Because wheezing makes it harder to breathe, it puts enormous strain on the lungs. The sounds associated with wheezing have been used to make diagnostics for centuries, but the physical mechanisms responsible for causing wheezing to occur are poorly understood, and there is no model to predict when to wheeze. gone happen. “

Dr Alastair Gregory, first author of the study, Department of Engineering, Cambridge University

Co-author Dr Anurag Agarwal, head of the engineering department’s acoustics lab, said he came up with the idea to study wheezing after a family vacation several years ago. “I started wheezing the first night we were there, which had never happened to me before,” he said. “And as an engineer who studies acoustics, my first thought was how cool it was for my body to make these noises. After a few days, I had real breathing problems, which made the novelty go away pretty quickly.

Agarwal’s wheezing was likely caused by an allergy to dust mites, which was easily treated with over-the-counter antihistamines. However, after chatting with a neighbor who is also a respiratory medicine specialist, he learned that although this is a common occurrence, the physical mechanisms that cause wheezing are somewhat mysterious.

“Since wheezing is associated with so many conditions, it’s hard to be sure what’s wrong with a patient based on wheezing alone, so we’re working to understand how wheezing sounds are produced so that diagnoses can be more precise ”. said Agarwal.

The lungs airways are a branching network of flexible tubes called bronchioles that gradually shorten and narrow as they sink into the lung.

In order to mimic this setup in the lab, the researchers modified a piece of equipment called Starling resistance, in which airflow is driven through thin, elastic tubes of varying lengths and thicknesses.

Co-author and computer vision specialist, Professor Joan Lasenby has developed a multi-camera stereoscopic technique to film air forced through tubes at varying degrees of tension, in order to observe the physical mechanisms that cause a wheezing.

“It surprised us how violent the mechanism of wheezing is,” said Gregory, who is also a junior researcher at Magdalene College. “We have found that there are two conditions for wheezing to occur: the first is that the pressure on the tubes is such that one or more bronchioles almost collapses, and the second is that the air is forced through the collapsed airway with enough force to cause oscillations. “

Once these conditions are met, the oscillations develop and are maintained by a flapping mechanism in which the waves moving back and forth have the same frequency as the opening and closing of the tube. “A similar phenomenon has been observed in the wings of planes when they break down, or in bridges when they collapse,” Agarwal said. “When the up and down vibrations are at the same frequency as the clockwise and counterclockwise torsional vibrations, we get a flutter which causes the structure to collapse. The same process is at work in the respiratory system.

From these observations, the researchers developed a “ tube law ” to predict when this potentially damaging oscillation could occur, based on the properties of the tube material, geometry and tension.

“We then use this law to build a model that can predict the onset of wheezing and might even be the basis for a cheaper and faster diagnosis of lung disease,” Gregory said. “Instead of expensive and time-consuming methods like X-rays or MRI, we wouldn’t need anything more than a microphone and a stethoscope.”

A diagnosis based on this method would work by using a microphone – the first tests were done using the built-in microphone on a normal smartphone – to record the frequency of the wheezing sound and use it to identify which bronchiole is close to collapse, and if the airways are unusually rigid or flexible in order to target treatment. The researchers hope that by uncovering changes in material properties due to wheezing and where the hissing sounds originate, the additional information will make it easier to distinguish between the different conditions, although more work in this area is needed. still needed.