Lung Development and Breathing Disorders
Lung Development and Breathing Disorders
By taking in oxygen from the air and expelling carbon dioxide, the lungs play a crucial role in maintaining life. The oxygen gathered by the lungs enters the blood as it circulates and is distributed to cells throughout the body. Of all the body's organs, the lungs, which are not yet fully mature at birth, account for the greatest number of health problems in infants and young children, including viral and bacterial infections, asthma, and obstruction from swallowing or inhaling foreign objects and substances.
During the prenatal stage, the lungs are among the last organs to finish developing. The surfactant coating that keeps them from sticking together isn't formed until the last month or two of gestation. The air sacs (alveoli) at the ends of the bronchial tubes are formed last and continue developing for some time after birth: the lungs of infants have only one-tenth as many air sacs as those of adults. The unborn baby, who is suspended in fluid, does not need lungs yet because the placenta exchanges oxygen and carbon dioxide, performing the task the lungs will later assume. The lungs themselves are also filled with fluid, most of which is expelled during the birth process. After birth, the chest expands and takes in air for the first time as the infant takes her first breath. After the first few breaths, the lungs should be fully expanded, and the air sacs fully inflated within an hour. Deep breathing begins about 30 seconds after birth, and respiration should total 30 to 60 breaths per minute by the time the infant is 90 minutes old. The lungs are pale pink at birth, eventually becoming darker as a result of inhaling dust and other particles.
Some babies need help breathing at birth, a condition known as perinatal asphyxia, which requires emergency treatment. Any liquids blocking the baby's airway are removed, and the infant is supplied with oxygen. In most cases, the initial gasp of oxygen is enough to initiate breathing. Sometimes a trachéal tube and/or artificial respiration are necessary. Asphyxia in newborns has been linked to low birth weight, late deliveries, and flattening or twisting of the umbilical cord during labor. An infant's risk of asphyxia is lower today than in the past thanks to medical advances that help physicians identify babies at risk for asphyxia before birth, enabling doctors to take precautions before or shortly after the baby is born. If the infant starts breathing within the first five minutes, lasting damage can be averted. In some cases where an infant is known to be at risk for asphyxia, an emergency delivery may be attempted either by forceps or cesarean section.
Newborns not suffering from asphyxia may still undergo acute respiratory distress from various causes. The most widespread is hyaline membrane disease, also known as Respiratory Distress Syndrome (RDS). Usually found in premature babies, it is caused by a lack of surfactant lining in the lungs, preventing the alveoli from functioning normally. At one time this condition was a leading cause of mortality in newborns, accounting for over 25,000 infant deaths per year. Advances in neonatal care since 1970 have increased the chances of survival from about 30% to over 75%. With the current treatment, which involves administering oxygen and intravenous fluids and using a breathing machine when necessary, the infant's condition usually improves dramatically within days. Another cause of respiratory distress in newborns is fetal lung fluid that is not properly absorbed at birth. Oxygen may need to be administered, but the fluid is usually absorbed within 24 hours. Meconium aspiration poses yet another danger for newborns. Meconium, the contents of the intestines before birth, can be aspirated at birth if it is expelled into the amniotic fluid, obstructing the infant's airway and threatening to cut off respiration. Meconium aspiration accounts for between 1 and 2% of all newborn deaths.
Several congenital defects can impair breathing, including tracheomalacia, in which the structures that support the airways are underdeveloped, causing them to narrow and become blocked; trachéal stenosis, a narrowing of the trachea itself due to cartilage, malformed arteries, cysts, and other causes; and disorders of the alveoli and their blood cells. Other congenital obstructions include choanal atresia, which obstructs the airway at the back of the nose, and obstructions of the larynx (voice box). In addition to obstructive disorders, infants sometimes suffer from problems with the central nervous system mechanism that controls breathing. Infants with apnea periodically stop breathing, a condition that can be triggered by an infection, a metabolic or cardiovascular disorder, maternal drug use, or a variety of other causes. Some cases of apnea, which is especially common in premature babies, resolve on their own. A related
Other respiratory disorders that can affect newborns include pulmonary edema (buildup of fluid in the lungs); neonatal pneumonia (usually caused by inhaling streptocuccus bacteria at birth); pulmonary hemorrhage (internal bleeding that fills a large part of the lung); congenital diaphragmatic hernias (in which the intestines protrude into the chest of the fetus, interfering with lung development); and obstruction caused by cardiovascular abnormalities.
Infants and children
Infants and children of all ages are subject to the most widespread respiratory disorder: the upper respiratory tract infection known as the common cold. Colds are caused by viruses transmitted through the air by sneezing and coughing or through touched surfaces that have had virus germs deposited on them by someone with a cold. Children get more colds than adults—often as many as three to nine in a single year. Symptoms—including sore throat, sneezing, nasal congestion, a runny nose, cough, or laryngitis—may end in three or four days, or they may last 10 days or longer. While the elusive cure for the common cold has yet to be found, acetominophen is generally recommended to bring down any associated fever. Another common illness associated with respiratory tract symptoms is influenza (flu). This viral infection is generally divided into three types—A, B, and C (C is the mildest; A is the most severe and long-lasting). Unlike colds, the flu can occur in epidemics, and it can lead to dangerous pulmonary complications. In addition to the upper and lower respiratory symptoms that characterize colds, flu symptoms can also include headaches, a high fever with chills, muscles aches, loss of appetite, and weakness. The flu can also produce gastrointestinal symptoms. Although the flu generally has to run its course—usually within five days—it should be monitored carefully because it can lead to secondary sinus or ear infections, and sometimes even to pneumonia.
Croup is an inflammation of the air passages that lead to the lungs. The larynx, trachea, or bronchi may be affected. In children under the age of three all three are typically involved, and the infection is a viral one. Symptoms include a "barking" cough, noisy (stridorous) breathing, breathing with difficulty, wheezing, and hoarseness. Croup can be dangerous because it can severely obstruct the breathing of young children, who have smaller airways than older children or adults. Signs of serious respiratory obstruction—requiring emergency medical treatment—include rapid, difficult breathing, inability to speak, drooling, increasing restlessness, sweating, and a rapid pulse. The most severe form of croup, epiglottitis, can completely block a child's breathing in four to 12 hours. It is treated by placing a tube in the trachea and administering oxygen.
It is not uncommon for a cold to lead to bronchitis, a lower respiratory inflammation of the trachea and bronchial tubes. When the larynx is also affected, the condition is known as laryngotracheobronchitis. Bronchitis can be caused by viruses, bacteria, or allergies. Acute bronchitis, usually caused by a cold virus, is a common childhood disease, especially in children under the age of four. It begins with a dry, hacking cough lasting up to three days, followed by a loose cough that produces thick mucous or sputum and that worsens at night. Since the virus itself cannot be treated with medication, treatment is limited to controlling the symptoms with either a cough suppressant such as dextromethorphan for a dry, hacking cough or an expectorant such as guaifenesin to help thin the sputum of a loose cough so it can be expelled, unclogging the airways. Children with bronchitis also needs to get plenty of rest so that the body can fight the infection. In cases where bronchial inflammation is caused by a bacterial infection, antibiotics such as erythromycin can be prescribed.
Bronchitis also occurs as a chronic ailment, with symptoms persisting over several weeks or longer or recurring frequently. In children, this type of bronchitis is generally caused by allergies (as opposed to adults, in whom it is often caused by smoking). The most effective way to treat chronic bronchitis in children is to identify any allergies that may be causing it and by avoiding the foods or other substances that trigger them. In addition, antihistamines can control the body's reaction to allergens, and, in the case of certain moderate to severe allergies, allergy shots can be an effective treatment method. Measures that can help prevent children from getting bronchitis include frequent hand washing to prevent the spread of germs and eliminating smoking from the home. Infants whose parents smoke are four times as likely to get bronchitis as those in non-smoking households.
Another lower respiratory inflammation that affects children (primarily infants between 2 and 10 months old) is bronchiolitis, a viral infection of the small airways that branch off the bronchi. The bronchioles swell and thicken, obstructing the air supply to the alveoli and making breathing difficult. Usually, this condition clears up by itself within a few days, but severe cases may require medical attention, including hospitalization to administer oxygen and hydration. In bronchiectasis, a condition arising from chronic inflammation of the airway (from infections or other causes), a portion of the bronchial tree is destroyed, resulting in a heavy sputumproducing cough and breathing difficulty. It is treated by antibiotics to clear up any residual infection, drainage of the sputum, and, in severe cases, surgical removal of the affected area.
Pneumonia, a serious lung inflammation that can be contracted by infants and children, has a variety of possible causes. It can be caused by a number of viruses, as well as bacteria including staphylococcus, chlamydia, and pneumococcus. (Newborns can acquire it from bacteria in the mother's body.) More rarely, it is caused by chemicals that are inhaled and damage the lungs. The most universal symptom of pneumonia is coughing. Other symptoms vary with the type of pneumonia and may include rapid breathing, chest pain, a high fever, and (in the case of viral pneumonia) vomiting. Since the introduction of antibiotics, pneumonia is no longer the health scourge it once was, but it is important for it to be correctly diagnosed (in an office examination that includes listening to chest sounds and possibly an χ ray) and treated. Newborns with pneumonia are usually hospitalized.
Asthma is a chronic, reversible respiratory disorder that involves obstruction and swelling of the airways to the lungs. The main symptoms of asthma are coughing, wheezing, and shortness of breath; other possible symptoms include fatigue, anxiety, and tightness in the chest. Nine to 10 million Americans suffer from asthma, about half of them children under the age of 16. In addition to allergens such as pollen, animal dander, dust, and foods, asthma can be triggered by a number of other factors, including certain activities (aerobic exercises such as running) and irritants such as tobacco smoke and certain chemical substances. It is possible to control asthma by avoiding known allergens and irritants, using medications that can prevent or alleviate the symptoms of asthma attacks, and receiving allergy shots to bolster the body's tolerance to allergens. Children often outgrow asthma when they reach adolescence or adulthood: in more than half, the condition resolves completely, while 10% only have occasional asthma attacks as adults.
Among the most serious childhood disorders affecting the lungs is cystic fibrosis, a genetic disease that disrupts the functioning of mucus-producing glands throughout the body, including the lungs. The condition results in abnormally thick, sticky mucus secretions that, in the case of the lungs, accumulate and interfere with normal respiration, also leading to chronic infections such as bronchitis and pneumonia and eventual deterioration of the lungs. (In the digestive system, these secretions prevent important digestive enzymes from the pancreas from reaching the intestines, impairing normal digestion.) Signs of cystic fibrosis include both digestive abnormalities (as well as the resulting weight loss and malnutrition) and respiratory symptoms, such as coughing and shortness of breath. Treatment consists of antibiotics to prevent respiratory infections, therapy to help loosen and expel excess phlegm, and enzyme supplements to aid digestion. The outlook for sufferers of cystic fibrosis is improving as new medications and improved methods of care are developed. The gene that causes the disease was isolated in 1989, opening the possibility of eventually conquering it through gene therapy.
After almost being eradicated in the United States in the 1950s, tuberculosis (TB) has become a cause for renewed concern since the 1980s, resurfacing primarily in certain high-risk groups (immigrants from Southeast Asia, the urban poor, and AIDS victims). Especially troublesome is the appearance of strains of tuberculosis that are resistant to the standard medications used to combat the disease, a development that occurs when patients do not complete the full course of treatment, allowing their infections to persist and become drug-resistant. Once contracted, tuberculosis can remain latent for some time, although skin scratch tests can detect it even in this phase. Once the disease becomes active, it causes coughing, fever, fatigue, and weight loss and is detectable by a chest χ ray and/or sputum culture. Once medication is begun, patients with the normal non-resistant forms of the illness become contagion-free in a matter of weeks, although it takes about two years of drug therapy for a complete cure. TB tests to detect the disease in its latent form are part of routine well-baby exams and are usually performed at the age of 12-15 months, before a child starts school, and during the teenage years.
In addition to the specific disorders discussed above, a common cause of lower respiratory problems in children is the aspiration of foreign objects. Although infants and young children swallow a wide variety of objects, some of the most common ones are bones, coins, nuts, and safety pins. Large objects can obstruct airways; smaller ones may go unnoticed at first but later cause a number of problems, including infection, inflammation, overinflation, and even partial collapse of the lungs. Many but not all aspirated objects are visible in an χ ray.
de Vries, Jan. Asthma and Bronchitis. Edinburgh: Mainstream Publishers, 1991.
Haas, Francois, and Sheila Sperber Haas. The Chronic Bronchitis and Emphysema Handbook. New York: Wiley, 1990.
Levitzky, Michael B. Pulmonary Physiology. New York: McGraw-Hill, 1986.
National Institutes of Health. Pediatric Respiratory Disorders. Bethesda, MD: Division of Lung Diseases, National Institutes of Health, 1986.
American Lung Association
Address: 1740 Broadway
New York, NY 10019
Telephone: (212) 315-8700
Asthma and Allergy Foundation of America
Address: 1125 15th Street NW, Suite 512
Washington DC 20005
Telephone: (202) 466-7643
Cystic Fibrosis Foundation
Address: 6931 Arlington Road, Suite 200
Bethesda, MD 20814
Telephone: (301) 951-4422; (800) FIGHTCF [344-4823]