Researchers Identify 'Violent' Processes That Cause Wheezing
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Researchers used modelling and high-speed video techniques to show what causes wheezing. Their results could be used as the basis for a cheaper and faster diagnostic for lung disease that requires just a stethoscope and microphone. For most people, wheezing is temporary and usually the result of a cold or mild allergic reaction. Regular or chronic wheazing is often a symptom of asthma or COPD.

The airways of the lung are a branching network of flexible tubes, called bronchioles, that gradually get shorter and narrower as they get deeper into the lung. In order to mimic this setup in the lab, the 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 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. 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 travelling 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.

This law is used to build a model that can predict the onset of wheezing and could even be the basis of a cheaper and faster diagnostic for lung disease. A diagnostic based on this method would work by using a microphone to record the frequency of the wheezing sound. It could identify which bronchiole is near collapse and whether the airways are unusually stiff or flexible in order to target treatment.