Breath of Fresh Air: Feature Articles
Chapter 1: What is Asthma?
A wise lung doctor once said, "Asthma is like love: everyone knows what it is but no one can agree on its definition." If you have experienced asthma, you probably have a pretty good idea of what this disease is for you: cough, wheezing, shortness of breath, tightness in the chest, itching under the chin, an uncomfortable awareness of your breathing, "noisy cats" singing in your chest, frightening attacks of not being able to catch your breath, etc. These are some of the symptoms of asthma.
The difficulty comes in that not everyone with asthma experiences the same symptom or group of symptoms. Also, many people with asthma have absolutely no symptoms for long periods at a time; what does it mean to have asthma but to have no symptoms of asthma? And any good definition should give some insight into what causes this condition in the first place, and how it is distinguished from other somewhat similar conditions that are definitely not the same, like bronchits or emphysema.
If we knew exactly what causes asthma perhaps we could be more precise in our definition. We don't the cause — or causes — of asthma, and we can't even say for sure if it is one disease or a group of diseases with very similar manifestations. Still, there is a lot that we do know about what makes one have the symptoms of asthma, including a lot more now than was known just ten years ago.
To begin, asthma is a disease of the bronchial tubes of the lungs. These are the passageways that begin with the windpipe and branch like a tree into thousands of smaller tubes, carrying air in and out of the lungs. Narrowing of these breathing tubes, the "bronchi" (pronounced "bronk' - eye"), leads to many of the symptoms of asthma: difficulty breathing results from the extra work involved with having to move air through these narrowed tubes; wheezes are the sound of air whistling through the narrowed pipes.
Persons with asthma have a condition that makes it possible for these bronchi to become abnormally narrowed. Although there is the potential for narrowing of the bronchi, they may remain open normally for long periods. The bronchi may stay widely open on their own, and of course keeping them open is also the goal of the treatment of asthma. A person with asthma whose air passageways are widely open will have normally functioning lungs and will have no breathing limitation whatsoever. That is why some persons with asthma are able to be professional athletes or to compete in the Olympics.
Understanding what asthma is, then, involves identifying what causes the potential for narrowing of the airways, a possibility not shared by persons without asthma, even if they go into a smokey room or hug the cat or run in a field of ragweed pollen. In recent years it has been found that the bronchi of persons with asthma show signs of inflammation, and it is believed that this inflammation is what makes the bronchi vulnerable to abnormal narrowing. The inflammation seems to be there all the time, even when one feels perfectly well. If stimulated in a certain way (for example, by cold air breathed deeply into the lungs), inflamed asthmatic bronchi contract and narrow; uninflamed, normal bronchi do not.
Inflammation can mean many different things in different circumstances, but in asthma we are referring to cells that come out of the blood and take up residence in the walls of the bronchial tubes. These are cells involved with allergic inflammation, called eosinophils and lymphocytes; they contain or can make powerful chemicals, capable of causing swelling of the walls of the bronchial tubes and damage to the inner layer of cells lining the bronchi. In the presence of this inflammation, the muscle that surrounds the bronchial tubes can contract and narrow the breathing passageways. This process may be familiar to you from pictures used in Primatene Mist television commercials: muscle contracting and narrowing the bronchi, then relaxing and allowing the tubes to fully open again. (The muscle cells that surround the bronchi are not controlled by your conscious brain; like the muscles that propel food through your stomach and intestines, they are not under your voluntary control.)
Also, with certain stimulation this inflammation of the bronchi can worsen, causing the walls of the tubes to swell and mucus to be secreted inside the tubes. Swollen, narrowed tubes filled with mucus: these are the circumstances where asthma causes symptoms -- breathing through these narrowed tubes becomes difficult, cough and raising phlegm may result.
In the end we have defined asthma as a tendency to develop abnormal narrowing of the bronchial tubes. A variety of things may stimulate asthmatic tubes to narrow — these are the "triggers" of asthma about which we will speak more in future issues of Breathing Easy. A certain kind of allergic inflammation gives the bronchi this abnormal tendency to narrow. What causes the bronchi to have this type of inflammation in the first place? No one knows for sure, although asthma research is bringing closer to the answers every day.