s the common dust mite, a close relative of spiders. The dust mite is so small that it is barely visible with the unaided eye, so it’s obviously shown greatly enlarged above. If you think you can get rid of dust mites in your home by frequent and thorough cleaning, think again. There may be thousands of dust mites in just one gram of dust! Regardless of how clean you keep your house, you can’t eliminate dust mites entirely. So why even bother trying? The feces of dust mites contain proteins that are a common trigger of asthma attacks.

Asthma is a chronic inflammatory disease of the airways in the lungs, in which the airways periodically become inflamed. As you can see in Figure 12.24, this causes swelling and narrowing of the airways, often accompanied by excessive mucus production. Symptoms of asthma include difficulty breathing, coughing, wheezing, shortness of breath, and chest tightness. Some people with asthma rarely experience symptoms, and then usually only in response to certain triggers in the environment. Other people may have symptoms almost all of the time.

Asthma is thought to be caused by a combination of genetic and environmental factors. A person with a family history of asthma is more likely to develop the disease. Dozens of genes have been found to be associated with asthma, many of which are related to the immune system. Additional risk factors include obesity and sleep apnea. Environmental factors trigger asthma attacks in people who have a genetic predisposition to the disease. Besides dust mite feces, triggers may include other allergens (such as pet dander, cockroaches, and mold), certain medications including aspirin, air pollution, and stress. Symptoms tend to be worse at night and early in the morning. They may also worsen during upper respiratory tract infections, strenuous exercise, or when the airways are exposed to cold air.

There is no cure for asthma at present, but the symptoms of asthma attacks usually can be reversed with the use of inhaled medications called bronchodilators (as shown in Figure 12.25). These medications soothe the constricted air passages and help to re-expand them, making breathing easier. The medications usually start to take effect almost immediately. Other medications can be taken for long-term control of the disease. These medications help prevent asthma attacks from occurring. Corticosteroids are generally considered the most effective treatment for long-term control. Another way to prevent asthma attacks is by avoiding triggers whenever possible.

Another common inflammatory disease of the respiratory tract is pneumonia. In pneumonia, inflammation affects primarily the alveoli, which are the tiny air sacs of the lungs. Inflammation causes some of the alveoli to become filled with fluid so that gas exchange cannot occur, as you can see illustrated in Figure 12.26. Symptoms of pneumonia typically include coughing, chest pain, difficulty breathing, and fever.

Pneumonia often develops as a consequence of an upper respiratory tract infection (such as the common cold or flu), especially in the very young and the elderly. It is usually caused by bacteria or viruses, although some cases may be caused by other microorganisms, such as fungi. The majority of cases are caused by just a few pathogens, the most common being the bacterium Streptococcus pneumoniae. Pneumonia is more likely to develop in people who have other lung diseases, such as asthma, a history of smoking, heart failure, or a weakened immune system.

Vaccines are available to prevent certain types of bacterial and viral pneumonia, including pneumonia caused by Streptococcus pneumoniae. Treatment of pneumonia depends on the cause. For example, if the disease is caused by bacteria, antibiotics are generally prescribed. In cases of severe pneumonia, hospitalization and supplemental oxygen may be required.

Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by chronic poor airflow due to increasing in-elasticity of lung tissue and breakdown of the walls of the alveoli. The main symptoms include shortness of breath and a cough that produces phlegm. These symptoms are usually present for a long period of time, and typically become worse over time. Eventually, walking up stairs and similar activities become difficult because of shortness of breath.

COPD formerly was referred to as chronic bronchitis or emphysema. Now, the term chronic bronchitis is used to refer to the symptoms of COPD, and the term emphysema is used to refer to the lung changes that occur with COPD. Some of these lung changes are shown in Figure 12.27 below. They include a breakdown of connective tissues that reduces the number and elasticity of alveoli. As a result, the patient can no longer fully exhale air from the lungs, so air becomes trapped in the lungs. Gas exchange is hampered and may lead to low oxygen levels, as well as too much carbon dioxide in the blood.

Smoking tobacco and vaping are the major cause of COPD, with a number of other factors such as air pollution and genetics playing smaller roles. Of people who are life-long smokers, about half will eventually develop COPD. Exposure to secondhand smoke in nonsmokers also increases the risk of COPD, and accounts for about 20 per cent of cases.  Most cases of COPD could have been prevented by never smoking or vaping. In people who have already been diagnosed with COPD, cessation of smoking or vaping can slow down the rate at which COPD worsens. People with COPD may be treated with supplemental oxygen and inhaled bronchodilators. These treatments may reduce the symptoms, but there is no cure for COPD except — in very severe cases — lung transplantation.

Lung cancer is a malignant tumor characterized by uncontrolled cell growth in tissues of the lung. The tumor may arise directly from lung tissue (primary lung cancer), or as a result of metastasis from cancer in another part of the body (secondary lung cancer). Primary lung cancer may also metastasize and spread to other parts of the body. Lung cancer develops after genetic damage to DNA that affects the normal functions of the cell. As more damage accumulates, the risk of cancer increases. The most common symptoms of lung cancer include coughing (especially coughing up blood), wheezing, shortness of breath, chest pain, and weight loss.

The major cause of primary lung cancer is tobacco use, which accounts for about 85 per cent of cases. Cigarette smoke contains numerous cancer-causing chemicals. Besides smoking, other potential causes of lung cancer include exposure to radon gas, asbestos, secondhand smoke, or other air pollutants. When tobacco smoking is combined with another risk factor (such as exposure to radon or asbestos), the risk of lung cancer is heightened. People who have close biological relatives with lung cancer are also at increased risk of developing the disease.

Most cases of lung cancer cannot be cured. In many people, the cancer has already spread beyond the original site by the time they have symptoms and seek medical attention. About ten per cent of people with lung cancer do not have symptoms when they are diagnosed, and the cancers are found when they have a chest X-ray for another problem. In part because of its typically late diagnosis, lung cancer is the most common cause of cancer-related death in men, and the second most common cause in women (after breast cancer). Approximately 21,000 Canadians die from lung cancer each year.  Common treatments for lung cancer include surgical removal of the tumor, radiation therapy, chemotherapy, or some combination of these three types of treatment.

Do you — or someone you love — snore? Snoring may be more than just an annoyance. It may also be a sign of a potentially dangerous and common disorder known as sleep apnea. Sleep apnea is characterized by pauses in breathing that occur most often because of physical blockage to airflow during sleep. When breathing is paused, carbon dioxide builds up in the bloodstream. The higher-than-normal level of carbon dioxide in the blood causes the respiratory centers in the brain to wake the person enough to start breathing normally. This reduces the carbon dioxide level, and the person falls back asleep. This occurs repeatedly throughout the night, causing serious disruption in sleep. Most people with sleep apnea are unaware that they have the disorder, because they don’t wake up fully enough to remember the repeated awakenings throughout the night. Instead, sleep apnea is more commonly recognized by other people who witness the episodes.

Figure 12.28 below shows how sleep apnea typically occurs. The muscle tone of the body normally relaxes during sleep, allowing the soft tissues in the throat to collapse and block the airway. The relaxation of muscles may be exacerbated by the use of alcohol, tranquilizers, or muscle relaxants. The risk of sleep apnea is greater in people who are overweight, smoke tobacco, or have diabetes. The disorder is also more likely to occur in older people and males. Common symptoms of sleep apnea include loud snoring, restless sleep, and daytime sleepiness and fatigue. Daytime sleepiness, in turn, increases the risk of driving and work-related accidents. Continued sleep deprivation may cause moodiness and belligerence. Lack of adequate oxygen to the body because of sleep apnea may also lead to other health problems, including fatty liver diseases and high blood pressure. Symptoms of sleep apnea may be present for years — or even decades — until (and if) a diagnosis is finally made.

Treatment of sleep apnea may include avoiding alcohol, quitting smoking, or losing weight. Elevating the upper body during sleep or sleeping on one’s side may help prevent airway collapse in people with sleep apnea.

Review

1. How can asthma attacks be prevented? How can symptoms of asthma attacks be controlled?.
2. How can pneumonia be prevented? How is it treated?
3. What is the difference between primary and secondary lung cancer? What is the major cause of primary lung cancer? Discuss lung cancer as a cause of death. How is lung cancer treated?
4. What is the difference between how COPD and pneumonia affect the alveoli?

CASE STUDY: COUGH THAT WON’T QUIT

Three weeks ago, 20-year-old Erica came down with symptoms typical of the common cold. She had a runny nose, fatigue, and a mild cough. Her symptoms were starting to improve, but recently, her cough has been getting worse. She is coughing up a lot of thick mucus, her throat is sore from frequent coughing, and her chest feels very congested. According to her grandmother, Erica has a “chest cold.” Erica is a smoker and wonders if her habit is making her cough worse. She decides that it’s time to see a doctor.

Dr. Choo examines Erica and asks about her symptoms and health history. She checks the level of oxygen in Erica’s blood by attaching a device called a pulse oximeter to Erica’s finger.

Dr. Choo concludes that Erica has bronchitis, which is an infection that commonly occurs after a person has a cold or flu. Bronchitis is sometimes referred to as a “chest cold,” so Erica’s grandmother was right! Bronchitis causes inflammation and a build up of mucus in the bronchial tubes in the chest.

Because bronchitis is usually caused by viruses and not bacteria, Dr. Choo tells Erica that antibiotics are not likely to help. Instead, she recommends that Erica try to thin out and remove the mucus by drinking plenty of fluids and using a humidifier or spending time in a steamy shower. She recommends that Erica get plenty of rest as well.

Dr. Choo also tells Erica some things not to do — most importantly, to stop smoking while she is sick, and to try to quit smoking in the long-term. She explains that smoking can make people more susceptible to bronchitis and can hinder recovery. Finally, she advises Erica to avoid taking over-the-counter cough suppressant medication.

Inhaling the moist air from a humidifier or steamy shower can feel particularly good if you have a respiratory system infection, such as bronchitis. The moist air helps to loosen and thin mucus in the respiratory system, allowing you to breathe easier.

In the beginning of this chapter, you learned about Erica, who developed acute bronchitis after getting a cold. She had a worsening cough, a sore throat due to coughing, and chest congestion. She was also coughing up thick mucus.

Acute bronchitis usually occurs after a cold or flu, usually due to the same viruses that cause cold or flu. Because bronchitis is not usually caused by bacteria (although it can be), in most cases, antibiotics are not an effective treatment.

Bronchitis affects the bronchial tubes, which, as you have learned, are air passages in the lower respiratory tract. The main bronchi branch off of the trachea and then branch into smaller bronchi, and then bronchioles. In bronchitis, the walls of the bronchi become inflamed, which makes them narrower. There is also excessive production of mucus in the bronchi, which further narrows the pathway where air can flow through. Figure 12.31, shows how bronchitis affects the bronchial tubes.

The treatment for most cases of bronchitis involves thinning and loosening the mucus so that it can be effectively coughed out of the airways. This can be done by drinking plenty of fluids, using humidifiers or steam, and — in some cases — using over-the-counter medications (such as expectorants). Dr. Choo recommended some of these treatments to Erica, and also warned against using cough suppressants. Cough suppressants work on the nervous system to suppress the cough reflex. When a patient has a “productive” cough (which means they are coughing up mucus), doctors generally advise them not to take cough suppressants, so that they can cough the mucus out of their bodies.

When Dr. Choo was examining Erica, she used a pulse oximeter to measure the oxygen level in her blood. Why did she do this? As you have learned, the bronchial tubes branch into bronchioles, which ultimately branch into the alveoli of the lungs. The alveoli are where gas exchange occurs between the air and the blood to take in oxygen and remove carbon dioxide and other wastes. By checking Erica’s blood oxygen level, Dr. Choo was making sure that her clogged airways were not impacting her level of much-needed oxygen.

Erica has acute bronchitis, but you may recall that chronic bronchitis was discussed earlier in this chapter (Section 13.5) as a term that describes the symptoms of chronic obstructive pulmonary disease (COPD). COPD is often due to tobacco smoking, and it causes damage to the walls of the alveoli. Acute bronchitis, on the other hand, typically occurs after a cold or flu, and involves inflammation and mucus build-up in the bronchial tubes. As implied by the difference in their names, chronic bronchitis is an ongoing, long-term condition, while acute bronchitis is likely to resolve relatively quickly with proper rest and treatment.

Erica uses e-cigarettes (vaping), so she is more likely to develop chronic respiratory conditions, such as COPD. As you have learned, smoking damages the respiratory system, along with many other systems of the body. Smoking and vaping increases the risk of respiratory infections, including bronchitis and flu, due to its damaging effects on the respiratory and immune systems. Dr. Choo strongly encouraged Erica to quit vaping, not only so that her acute bronchitis resolves, but so that she can avoid future infections and other negative health outcomes associated with vaping and smoking, including COPD and lung cancer.

As you have learned in this chapter, the respiratory system is critical to carry out the gas exchange necessary for life’s functions, and to protect the body from pathogens and other potentially harmful substances in the air. But this ability to interface with the outside air has a cost. The respiratory system is prone to infections, as well as damage and other negative effects from allergens, mold, air pollution, cigarette smoke and vaping. While exposure to most of these things cannot be avoided, not smoking is an important step you can take to protect this organ system — as well as many other systems of your body.