Dr
John Miller, left, and
Dr Gerard Cox
Photo
courtesy of SJHC |
Ask any asthma
patient to empty their pockets and there, among the lint, keys and coins, you'll
no doubt find their trusty puffer. But a team of Canadian physicians says bronchial
thermoplasty (BT), an experimental surgical treatment for asthma, could reduce
your patients' dependence on these rescue meds. FEWER
SYMPTOMS
BT is the focus of the Asthma Intervention Research Trial,
headed up by respirologist Dr Gerard Cox and thoracic surgeon Dr John Miller of
St Joseph's Healthcare in Hamilton. The procedure uses a surgical probe —
deployed during a bronchoscopic intervention in patients under conscious sedation
— to deliver heat-generating radiofrequency pulses that reduce the amount
of bronchial smooth muscle tissue. Asthmatics often
have more smooth muscle tissue lining their airways than non-asthmatics. The contraction
of this tissue is thought to be an important contributor to bronchial constriction
and airway hyperresponsiveness. "It's possible — but speculative — to
say that BT returns the smooth muscle to normal amounts," notes Dr Cox. The
team monitored 52 moderate-to-severe asthmatics treated with BT over a year. They
found that the BT-treated patients had fewer mild exacerbations of symptoms than
controls, based on levels of peak expiratory flow, less need for rescue medications
and less sleep disruption due to breathing difficulty. The BT patients also saw
an increase in symptom-free days, totalling eight months per year compared with
three months in controls. Additionally, treated subjects showed significant improvements
of their Asthma Quality of Life Questionnaire and Asthma Control Questionnaire
scores, improvements that persisted up to the end of the study period. The report
appears in the March 29 issue of the New England Journal of Medicine. BARELY
A SCRATCH
The outpatient procedure involves three visits. "If everything
looks good following the first session, we continue with two more. The whole treatment
may involve 150 zaps, in total," explains Dr Miller. The injury inflicted by BT
on lung tissues produces irritation in all recipients of the treatment, though
Dr Miller likens it to that sustained from a dental procedure: "There will be
some pain, as well as different and new sensations. Post-surgery side effects
can become important complications in cases of very severe asthma, but for the
most part the irritation clears up within two weeks." The
whole airway-burning dimension of BT might seem a little extreme, but Dr Cox points
out that that, in fact, is the beauty of it: "Muscle cells, which have evolved
to a highly complex state, don't repair as easily as other tissues also injured
in the procedure," he explains. Dr Miller adds, "We understand that the effects
of BT will be permanent, and the smooth muscle reduction will last." The
procedure is currently limited, in part, by the size of the BT probe. "Miniaturizing
is technically possible," explains Dr Cox, "but it would take another round of
development work." For the moment the team is focusing on assessing how much BT
will allow them to reduce medication doses and treatment costs. "For some asthmatics,
the technique may provide significant improvement, though, and further modifications
might not be necessary. At this point, it should beconsidered as an adjunct to
other treatments." BT isn't yet approved for clinical
use in Canada. "It's only available in the context of a trial," explains Dr Miller.
"The expected date of routine availability is about two to three years."
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