Its all in your head, silly.

Depends on whether you believe in a key or primary role of lung tissue
damage.  Exercises for slowing down my breathing rate quickly converted
me from being a true believer in asthma drugs.  Breathing controls
supposedly fundamental things like the lungs' allergic response.
Asthma can be caused by reflux (GERD) and this doesn't fit in with the
primacy of lung damage stuff either.
Normally Occam's Razor (concentrating on the simplest argument first)
would apply, but the technicalities of medicine prevent this.  Apart
from people expecting pills etc and not instruction in breathing
techniques from a doctor, the key aspect of breathing, that is
sufficiently doctor-friendly, is measuring air breathed in and out.
Pulse oximetry is tied up with this central concept. Peakflow
measurements are of course in the present state of affairs essential to
save lives, but seem to exclude a concentration on routines such as
pursed lip breathing, which - obviously - increase pressure in the
abdomen like karate maneuvers and hence the flow of blood to the lungs
(Frank-Starling mechanism) by squeezing the vena cava inferior.
Other breathing-related things like chi, prana, getting a feeling for
the "tanden" and pressure in the abdomen pass the Occam's Razor
test but cannot be measured, because they are felt as sensations and
seem to be dependent on the culture you happen to live in.
So studying the details of lung tissue damage would not seem to help,
but rather hinder, getting a fuller picture of asthma.
Sifting the evidence from all sources including oriental breathing
techniques would seem to point to asthma being dependent on a lack of
sufficient blood in the lungs.  If too much air in the lungs
(hyperventilation) is a key symptom of asthma, then it would be obvious
to try to increase the so unfortunately non-measurable lung blood
supply.  Buteyko has shown that simply reducing the air supply rate
(demonizing deep breathing) is merely a symptomatic approach.
Leaving out the safety aspect, tensing the front upper abdominal
muscles inward and upward while slowly breathing in seems to unlock the
chest.  The shoulders can move up naturally and there is a sort of
bronchodilator sensation at the top of the chest. The heart seems to
pump more blood. Either a real increased blood flow into the lungs or
some reflex is concerned.
All this  however must necessarily be banned from medicine (but not
from physiotherapy) because the factors involved cannot be truly
identified, let alone measured.  Regards, Richard Friedel.