Asthma

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General Asthma Information

Asthma & Allergy Week

The Pathophysiology of Asthma: Understanding Treatment

Have you ever tried breathing through a straw?  It’s not easy, but that’s what an asthma exacerbation or “attack” can feel like, sometimes several times a day, to the almost 25 million asthma sufferers in America.  An asthma attack occurs when the airway tubes through which oxygen-containing air should flow freely into our lungs become constricted.  Airways are encircled by smooth muscle. When the muscle contracts it closes the airways like a tight rubber band would.

Why and how does this happen? In asthma the airways undergo repeated episodes of inflammation caused by inhaling allergic and chemical triggers, cold air, or during exercise.  Inflammation occurs when specialized immune cells move through the blood to the airways.  Other cells that reside in the airways, such as epithelial cells that line the air tubes, become “activated” and initiate the inflammatory response.  Because asthma triggers are different between people, the nature of the inflammation differs too.  However, cells called eosinophils are recognized to be principal constituents, as are lymphocytes, neutrophils, and mast cells.  Inflammation causes airway smooth muscle to contract excessively, but also leads to swelling of the airway wall and the release of mucous into the airways.  These responses narrow and plug the airways, which causes the tight chest, wheezing, and difficulty in breathing that are hallmark features of an asthma attack.  This is also the reason that asthmatics have so-called “twitchy” airways that predispose them to having attacks.

New breakthroughs in understanding asthma pathogenesis show the lung, in particular the airway wall itself, to be structurally modified (remodeled) in asthma.  Even from birth, before exposure to triggers that cause asthma attacks, the airways may be different or undergo structural changes that allow inflammation to cause asthma symptoms later in life.  We now appreciate that during the course of asthma, when lung function declines over many years, airway remolding continues.  The key feature of airway wall remodeling that contributes to asthma symptoms is that the amount and thickness of the airway smooth muscle greatly increases, due to fibrosis (scarring) in and around the muscle.  We also now know that epithelial cells from asthmatics are intrinsically different, and are not able to undergo responses to fully repair the airways after episodes of inflammation.

If inflammation and acute airway responses are not prevented or reversed with appropriate medication, asthma attacks can be fatal.  More usually, disease symptoms will worsen over time.  Prescription medications for asthma fall mainly into two categories: relievers and controllers.  Relievers are taken in inhaled form as needed using a so-called “puffer”.  The drugs typically bind to β2-receptors on the airway smooth muscle, causing it to relax and re-open the airway.  Controllers are usually taken regularly to inhibit the development of inflammation, and prevent the occurrence of asthma attacks.  In most cases, controller asthma medications are corticosteroids.  Optimal use of controller and reliever medications, often taken as a combination drug, requires training by a physician or health professional and practice by the patient to ensure the right amount of drug is taken and that it is taken correctly.

Despite the fact that most individuals can achieve satisfactory control of their asthma with reliever and controller medications, gaining therapeutic control of their disease is difficult for some.  These patients can be relatively unresponsive to inhaled steroids, and require high doses of oral steroids to control airway inflammation.  Due to the poor control of their disease, these patients suffer frequent attacks, and have poor lung function, even between episodes of “attack”. The airways of such individuals often show extensive airway remodeling, and a unique inflammation profile.

We are only beginning to understand the reasons for the airways inflammation in asthma.  A primary focus of current asthma research is aimed at getting better understanding of the origins, and natural history of asthma and its evolution to a severe, difficult-to-treat status.  Understanding these issues and the biology of asthma through extensive research effort is essential to pioneer the development of useful new drugs for treating asthma.

SourceAndrew Halayko, PhD —  Chair, ATS Assembly on Respiratory Structure and Function

Four Facts About Asthma

  • More than 25 million children and adults live with asthma all over the U.S., making it one of the most common and costly diseases.  Of those reporting an asthma attack in 2008:
    • One in seven had an asthma attack that required urgent outpatient care.
    • 41.8 % missed school or work due to asthma.
  • Low income and minority children bear the heaviest burden of asthma, including death.
  • Early childhood food allergies heighten the risk for developing asthma later in life.
  • Each year 3000 US asthma deaths occur.
(Source AAFA.org)