Chapter 1

Understanding Asthma Basics

IN THIS CHAPTER

Understanding what asthma is and who gets it

Digging into the types of asthma

Figuring out if you have asthma

Creating an asthma management plan

According to many experts, asthma is now a global epidemic, and its prevalence and severity continue to grow in many parts of the world, including the United States, Western Europe, Australia, and New Zealand. More than 25 million people in the United States alone and more than 330 million globally have some form of asthma. Taking care of asthma means taking care of your whole body — from your brain to your nose to your lungs — and we are here to help you along the journey as you discover what asthma is, how to treat and manage it, and how to prevent complications.

This chapter starts with the basics of asthma: what it is and how it affects you. Although much of this may seem like high school biology, it’s helpful to understand the contributing factors of asthma, as well as how to live a full life with the condition. You may be surprised to also find out who else lives with asthma since it affects so many people … even famous ones, as we highlight in the sidebar “Famous folks with asthma.”

Defining Asthma

You or someone you love has just been diagnosed with asthma. That isn’t easy to hear, and it’s natural to feel afraid or overwhelmed by this unsettling news. The good news is that scientists now know more than ever before about asthma and how to manage it, and the following sections will help you develop a basic understanding of how asthma affects you.

Asthma is a chronic condition that starts with the immune system and can impact many organs, including the lungs. A wide range of factors can trigger an asthma attack or flare: exercise, cold air, a virus, pollution, smoke, and, for many, a host of allergens. In fact, about 80 percent of children with asthma also have allergies. We talk more about allergies and other asthma triggers in Chapter 6.

Your lung airways are vital to your health. This network of bronchial tubes enables your lungs to absorb oxygen into the blood and get rid of carbon dioxide; the process is called respiration or breathing. Most people take breathing for granted; you usually don’t need to even think about it unless something interferes with the process by obstructing your airways.

How normal breathing works

To better understand how asthma adversely affects your airways, consider what happens in normal breathing:

• The air you inhale flows into your nose and/or mouth and into your trachea, or windpipe.
• Your trachea then divides in the lung into right and left main bronchi, or branches, funneling the air into each of your lungs.
• The main bronchi continue branching out into your lungs and dividing into a network of airways called bronchial tubes. The outside of your bronchial tubes consists of layers of muscles that relax and tighten as you inhale and exhale. Doctors refer to airway relaxation as bronchodilation and to the tightening that can help your lungs push out air when you exhale as bronchoconstriction.
• Your network of airways ultimately leads to the alveoli, tiny air sacs that look like small clusters of grapes. They contain blood vessels and provide the means for vital respiratory exchange. Oxygen from the air you breathe is absorbed into the bloodstream, while carbon dioxide gas from your blood exits your body as you exhale. In asthma, airway obstruction is most often the result of an underlying airway inflammation that leads to one or more of the following inflammatory responses: airway hyperresponsiveness, airway constriction, or airway congestion. (See the next section for more information.) Eventually, these inflammatory responses can lead to a vicious cycle in which your airways become more and more sensitive and inflamed because they’re constantly reacting to allergens, irritants, and other factors.

What you can’t see can hurt you

If your lungs were external organs — like gills — or if your body were transparent so that you could see what happens internally, more doctors would treat asthma earlier and more aggressively, because you and your doctor could easily see how the underlying disease affects you.

As we explain in the section “Testing your lungs,” later in the chapter, you need to make sure that your doctor performs appropriate pulmonary (lung) function tests if you have bouts of wheezing, recurring coughs, lingering colds, or other symptoms that may indicate an underlying respiratory ailment.

How airway obstruction develops

Here’s an overview of how the mechanisms of asthma interact. Although we’ve itemized these processes to explain them, keep in mind that they’re often ongoing events that can occur simultaneously in your lungs. As you read these descriptions, take a look at Figure 1-1, which compares a normal airway with an asthmatic airway.

• Airway constriction: When a trigger or precipitating factor irritates your airways, causing the release of chemical mediators such as histamine and leukotrienes (see Chapter 13) from the mast cells — which release chemical mediators that cause inflammatory responses — of the epithelium (the lining of the airway), the muscles around your bronchial tubes can tighten, leading to airway constriction. This process results in narrowing airways and breathing difficulty. Airway constriction can also occur in people who don’t have asthma or allergies if they’re exposed to substances that can harm their respiratory systems, such as poisonous gases or smoke from a burning building.
• Airway hyperresponsiveness: The underlying airway inflammation in asthma can cause airway hyperresponsiveness as the muscles around your bronchial tubes twitch or feel ticklish. This twitchy or ticklish feeling indicates that your muscles overreact and tighten, causing acute bronchoconstriction or bronchospasms even if you’re exposed only to otherwise harmless substances, such as allergens and irritants that rarely provoke reactions in people without asthma and allergies (see the section “Uncovering the Many Facets of Asthma,” later in this chapter).
• Airway congestion: Mucus and fluids are released as part of the inflammatory process and can accumulate in your airways, overwhelming the cilia (tiny hairlike projections from certain cells that sweep debris-laden mucus through your airways) and leading to airway congestion. This accumulation of mucus and fluids may make you feel the urge to cough up phlegm to relieve your chest congestion.

  FIGURE 1-1: A normal airway and an asthmatic airway. Note the muscle contractions (bronchospasms) and airway inflammation.

• Airway edema: The long-term release of inflammatory fluids in constricted, hyperresponsive, and congested airways can lead to airway edema (swelling of the airway), causing bronchial tubes to become more rigid and further interfering with airflow. In severe cases of airway congestion and edema, a chronic buildup of mucus secretion leads to the formation of mucus plugs in the airway, which limits airflow.
• Airway remodeling: If airway inflammation is left untreated or poorly managed for many years, the constant injury to your bronchial tubes due to ongoing airway constriction, airway hyperresponsiveness, and airway congestion can lead to airway remodeling, as scar tissue permanently replaces your normal airway tissue. As a result of airway remodeling, airway obstruction can persist and may not respond to treatment, leading to the eventual loss of your airway function as well as potentially irreversible lung damage.
• Cellular infiltration: This complex cellular mechanism, characterized by either predominant eosinophils or neutrophils, is involved in the airway remodeling seen in chronic asthma. As researchers continue to gain a greater understanding of this process, improved novel therapeutic approaches will allow for more targeted treatments of asthma and allergic diseases (see Chapter 13).

This vicious cycle of asthma can develop gradually, over hours or even days following exposure to triggers or precipitating factors. After this cycle is set in motion, you can suffer severe and long-lasting consequences.

Understanding Who Gets Asthma and Why

The strongest predictor that an individual may develop asthma is a family history of allergies and asthma and/or atopy, an inherited tendency to develop hypersensitivities to allergic triggers. This tendency is almost always due to an overactive immune system that produces elevated levels of immunoglobulin E (IgE) antibodies to allergens. (See Chapter 11 for an extensive discussion of this process.)

The predisposition to asthma is inherited. This genetic inheritance can be a significant factor in developing the condition: Two-thirds of asthma patients have a family member who also has the disease.

Most cases of asthma are of an allergic nature (known as allergic asthma), and usually begin to manifest during childhood, affecting boys more often than girls. In fact, asthma is the most common chronic disease of childhood. Other allergic...