In a recent study at the University of Cambridge, researchers found the ‘violent’ physical processes at work inside the lungs which cause wheezing, a condition that affects up to a quarter of the world’s population.
They 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 of a cheaper and faster diagnostic for lung disease that requires just a stethoscope and a microphone.
At some point, most of us have experienced wheezing, a high-pitched whistling sound made while breathing.
For most people, the phenomenon is temporary and usually results from 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.
In the study, researchers modified a piece of equipment called a Starling resistor, in which airflow is driven through thin elastic tubes of various lengths and thicknesses.
They then developed a multi-camera stereoscopy technique to film the air being forced through the tubes at different degrees of tension, in order to observe the physical mechanisms that cause wheezing.
They 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 of the bronchioles nearly collapses, and the second is that air is forced through the collapsed airway with enough force to drive oscillations.
Once these conditions are met, the oscillations grow and are sustained by a flutter mechanism in which waves traveling from front to back have the same frequency as the opening and closing of the tube.
Using these observations, the researchers developed a ‘tube law’ in order to predict when this potentially damaging oscillation might occur, depending on the tube’s material properties, geometry, and amount of tension.
The team says a diagnostic based on this method would work by using a microphone.
Early tests were done using the in-built microphone on a normal smartphone, to record the frequency of the wheezing sound and use this to identify which bronchiole is near collapse, and whether the airways are unusually stiff or flexible in order to target treatment.
The researchers hope that by finding changes in material properties from wheezing, and locations that wheezes come from, the additional information will make it easier to distinguish between different conditions.
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The study was published in the Royal Society Open Science and conducted by Dr. Alastair Gregory et al.
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