The ‘violent’ processes associated with wheezing

The researchers, from the University of Cambridge, used modelling and high-speed video techniques to show what causes wheezing and how to predict it. The results are reported in the journal Royal Society Open Science. “Because wheezing makes it harder to breathe, it puts an enormous amount of pressure on the lungs,” said first author Dr Alastair Gregory from Cambridge’s Department of Engineering. “The sounds associated with wheezing have been used to make diagnoses for centuries, but the physical mechanisms responsible for the onset of wheezing are poorly understood, and there is no model for predicting when wheezing will occur.” Co-author Dr Anurag Agarwal, Head of the Acoustics lab in the Department of Engineering, said “since wheezing is associated with so many conditions, it is difficult to be sure of what is wrong with a patient just based on the wheeze, so we’re working on understanding how wheezing sounds are produced so that diagnoses can be more specific”.

In order to mimic the pulmonary system in the lab, the researchers modified a Starling resistor, in which airflow is driven through thin elastic tubes of various lengths and thicknesses. Co-author and computer vision specialist Professor Joan Lasenby 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. Gregory, who is also a Junior Research Fellow at Magdalene College mentions “we 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 though 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 the amount of tension. “We then use this law 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,” said Gregory. “Instead of expensive and time-consuming methods such as x-rays or MRI, we wouldn’t need anything more than a microphone and a stethoscope.”

Source: Cambridge news release