But We Just Got a New Clue
From: Sciencealert.com
By David Nield, February 26, 2021 – Wheezing
is a common occurrence that most of us will have experienced, whether
temporarily through something like hayfever or a cold, or more long-term
through a condition such as asthma or chronic obstructive pulmonary
disease (COPD). But scientists don't understand much about why it happens.
New research has used a combination of
modelling and high-resolution video to try and shed some light on the
mechanisms of wheezing, finding that there's a "violent" process that
can cause our lung pipes to make these raspy sounds.
With this new information available, the
team is hoping that wheezing might be better understood and diagnosed in the
future.
"Because wheezing makes it harder
to breathe, it puts an enormous amount of pressure on the lungs," says
engineer Alastair Gregory, from the University of Cambridge in the UK.
"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."
To get to the bottom of wheezing,
scientists had to get to the end of the flexible bronchiole tubes that make up
the branching network in the lungs. They built their own lung substitute by
adapting a device called a Starling resistor, made up of thin elastic
tubes of varying lengths and thicknesses.
Air was forced through the tubes at
different degrees of tension and then filmed with a multi-camera stereoscopy
setup. The scientists were then able to observe how wheezing might begin and be
sustained, through a series of oscillations in the tubes (or in the lungs).
"It surprised us just how violent
the mechanism of wheezing is," says Gregory.
"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 through the collapsed airway with enough force to drive
oscillations."
In either case, the oscillations are
sustained through a fluttering mechanism, where the travelling waves of air
have the same frequency as the opening and closing of the tube. The same sort
of resonance scenario can collapse bridges and cause aircraft wings to
fail, which shows how damaging it could be to the lungs.
The scientists went on to develop a
'tube law', which factors in the material properties and the geometry of the
tubes, as well as the amount of tension they're under, to calculate when
oscillations might occur. If the law can be adapted to the human lungs, we
might have a new way of analyzing wheezes and identifying both the type and the
location of serious bronchial problems.
More work is going to be needed to
fine-tune the system and better pick up on wheezing sounds, but the researchers
are hopeful that a simple audio recording setup could in some circumstances
replace X-rays and MRI scans, which are expensive and time-consuming to
operate.
"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," says engineer
Anurag Agarwal, from the University of Cambridge.
The research has been published in Royal Society Open Science.
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