Asthma

What is asthma?

Asthma is a chronic inflammation of the bronchial tubes (airways) that causes swelling and narrowing (constriction) of the airways. The result is difficulty breathing. The bronchial narrowing is usually either totally or at least partially reversible with treatments.

Bronchial tubes that are chronically inflamed may become overly sensitive to allergens (specific triggers) or irritants (nonspecific triggers). The airways may become "twitchy" and remain in a state of heightened sensitivity. This is called "bronchial hyperreactivity" (BHR). It is likely that there is a spectrum of bronchial hyperreactivity in all individuals. However, it is clear that asthmatics and allergic individuals (without apparent asthma) have a greater degree of bronchial hyperreactivity than nonasthmatic and nonallergic people. In sensitive individuals, the bronchial tubes are more likely to swell and constrict when exposed to triggers such as allergens, tobacco smoke, or exercise. Amongst asthmatics, some may have mild BHR and no symptoms while others may have severe BHR and chronic symptoms.

Asthma affects people differently. Each individual is unique in their degree of reactivity to environmental triggers. This naturally influences the type and dose of medication prescribed, which may vary from one individual to another.

From the past to the present

Physicians in ancient Greece used the word asthma to describe breathlessness or gasping. They believed that asthma was derived from internal imbalances, which could be restored by healthy diet, plant and animal remedies, or lifestyle changes.

Allergy jargon

Asthma is derived from the Greek word Panos, meaning panting.

Chinese healers understood that xiao-chiran, or "wheezy breathing," was a sign of imbalance in the life force they called qi. They restored qi by means of herbs, acupuncture, massage, diet, and exercise.

The Hindu philosophers connected the soul and breath as part of the mind, body, and spirit connection. Yoga uses control of breathing to enhance meditation. Indian physicians taught these breathing techniques to help manage asthma.

Allergy fact

Maimonides was a renowned 12th-century rabbi and physician who practiced in the court of the sultan of Egypt. He recommended to one of the Royal Princes with asthma that he eat, drink, and sleep less. He also advised that he engage in less sexual activity, avoid the polluted city environment, and eat a specific remedy-chicken soup.

The balance of the "four humors," which was derived from the Greco-Roman times, influenced European medicine until the middle of the 18th century. In a healthy person, the four humors, or bodily fluids -- blood, black bile, yellow bile, and phlegm -- were in balance. An excess of one of these humors determined what kinds of disorders were present. Asthmatics who were noted for their coughing, congestion, and excess mucus (phlegm) production were therefore regarded as "phlegmatic."

By the 1800s, aided by the invention of the stethoscope, physicians began to recognize asthma as a specific disease. However, patients still requested the traditional treatments of the day, such as bloodletting, herbs, and smoking tobacco. These methods were used for a variety of conditions, including asthma. Of the many remedies that were advertised for asthma throughout the 19th century, none were particularly helpful.

Allergy fact

As early as 1892, the famous Canadian-American physician Sir William Osler suggested that inflammation played an important role in asthma.

Bronchial dilators first appeared in the 1930s and were improved in the 1950s. Shortly thereafter, corticosteroid drugs that treated inflammation appeared and have become the mainstay of therapy used today.

The scope of the problem

Asthma is now the most common chronic illness in children, affecting one in every 15. In North America, 5% of adults are also afflicted. In all, there are about 1 million Canadians and 15 million Americans who suffer from this disease.

The number of new cases and the yearly rate of hospitalization for asthma have increased about 30% over the past 20 years. Even with advances in treatment, asthma deaths among young people have more that doubled.

Allergy fact

There are about 5,000 deaths annually from asthma in the U.S. and about 500 deaths per year in Canada.

Normal bronchial tubes

Before we can appreciate how asthma affects the bronchial airways, we should first take a quick look at the structure and function of normal bronchial tubes.

The air we breathe in through our nose and mouth passes through the vocal cords (larynx) and into the windpipe (trachea). The air then enters the lungs by way of two large air passages (bronchi), one for each lung. The bronchi divide within each lung into smaller and smaller air tubes (bronchioles), just like branches of an inverted tree. Inhaled air is brought through these airways to the millions of tiny air sacs (alveoli) that are contained in the lungs. Oxygen (O₂) passes from the air sacs into the bloodstream through numerous tiny blood vessels called capillaries. Similarly, the body's waste product, carbon dioxide (CO₂), is returned to the air sacs and then eliminated upon each exhalation.

Normal bronchial tubes allow rapid passage of air in and out of the lungs to ensure that the levels of O₂ and CO₂ remain constant in the bloodstream. The outer walls of the bronchial tubes are surrounded by smooth muscles that contract and relax automatically with each breath. This allows the required amount of air to enter and exit the lungs to achieve this normal exchange of O₂ and CO₂. The contraction and relaxation of the bronchial smooth muscles are controlled by two different nervous systems that work in harmony to keep the airways open.

The inner lining of the bronchial tubes, called the bronchial mucosa, contains: (1) mucus glands that produce just enough mucus to properly lubricate the airways; and (2) a variety of so-called inflammatory cells, such as eosinophils, lymphocytes, and mast cells. These cells are designed to protect the bronchial mucosa from the microorganisms, allergens, and irritants we inhale, and which can cause the bronchial tissue to swell. Remember, however, that these inflammatory cells are also important players in the allergic reaction. Therefore, the presence of these cells in the bronchial tubes causes them to be a prime target for allergic inflammation

How does asthma affect breathing?

Asthma At A Glance

• Asthma is a chronic inflammation of the bronchial tubes (airways) that causes swelling and narrowing (constriction) of the airways. The bronchial narrowing is usually either totally or at least partially reversible with treatments.
• Asthma is now the most common chronic illness in children, affecting one in every 15.
• Asthma involves only the bronchial tubes and usually does not affect the air sacs or the lung tissue. The narrowing that occurs in asthma is caused by three major factors: inflammation, bronchospasm, and hyperreactivity.
• Allergy can play a role in some, but not all, asthma patients.
• Many factors can precipitate asthma attacks and are they are classified as either allergens or irritants.
• Symptoms of asthma include shortness of breath, wheezing, cough, and chest tightness.
• Asthma is usually diagnosed based on the presence of wheezing and confirmed with breathing tests.
• Chest X-rays are usually normal in asthma patients.
• Avoiding precipitating factors is important in the management of asthma.
• Medications can be used to reverse or prevent bronchospasm in patients with asthma.

References: Murray, J., Nadel, J. (2000). Textbook of Respiratory Medicine. Third edition. Philadelphia: W.B. Saunders Company.

Medically Reviewed By: Ellen Reich, MD, Board Certified in Allergy and Immunology, Board Certified in Pediatrics