Chronic Respiratory Diseases

CHRONIC RESPIRATORY DISEASES

Chronic respiratory diseases include disorders that affect any part of the respiratory system, not only the lung but also the upper airway (nose, mouth, pharynx, larynx, and trachea), the chest wall and diaphragm, and the neuromuscular system that provides the power for breathing. Prolonged (chronic) diseases and disorders of the respiratory system in adults are those conditions that are present for months to years, and are treatable but generally not curable. Successful medical management of any chronic respiratory disease depends upon evaluating the patient as a whole and assessing the structure and function of the entire respiratory system.

The chronic diseases of the respiratory system collectively result in profound human suffering, mortality, and economic loss. For example, an estimated 163,000 Americans will die of cancer of the respiratory system in 2001. Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States (behind heart diseases, cancer, and stroke) and now kills about 113,000 Americans annually. The death rate from COPD rose 44.5 percent between 1979 and 1997, an increase that was the highest among the top ten causes of death in the United States. Experts estimate that about 30 million Americans have COPD, and only about half of these have been evaluated and diagnosed. The total economic impact of COPD in the country is estimated to be about $31.9 billion annually.

The huge impact of lung cancer, COPD, and other chronic respiratory diseases in our society is especially sobering in light of the fact that many of these conditions are preventable. The use of tobacco is the leading cause of preventable illness and death in the United States, accounting for about 430,000 deaths, or about 20 percent of all deaths, annually. Cigarette smoking is the primary risk factor for the development of COPD and lung cancer. About 25 percent of all Americans smoke cigarettes, and, tragically, 3,000 young Americans take up the smoking habit every day, greatly increasing their risk of dying prematurely from COPD, lung cancer, heart disease, or some other smoking-related disease. It is alarming that the percentage of high school and college students who smoke cigarettes increased during the early 1990s.

There are relatively few symptoms of respiratory disease, whether it be acute or chronic, as a diseased respiratory system has a limited number of clinical expressions. These include shortness of breath (dyspnea); cough, with or without phlegm (sputum) production; high-pitched continuous

Figure 1

breathing noise (wheezing); chest tightness; coughing up blood (hemoptysis); and chest pain. Uncommonly, patients with chronic respiratory disease are free of symptoms (asymptomatic) but have a disease process that is discovered incidentally, such as by a routine chest X-ray. Respiratory symptoms may be the early warning sign of chronic respiratory disease, but, unfortunately, they are commonly ignored, dismissed as being normal, or mistakenly attributed to aging or alternative disorders.

The medical evaluation of a patient with a suspected chronic respiratory disease starts with the physician's taking a detailed medical history, with particular attention to the symptoms listed above and their timing (see Figure 1). A thorough history of respiratory illness always includes attention to relevant factors such as tobacco use, occupational and environmental exposure to noxious respiratory agents, travel, hobbies, immunizations, family medical history, current and prior medications, general medical health, and comorbid conditions, to name just a few relevant components. The medical history is followed by a physical examination, which must be complete in order to detect both pulmonary and nonpulmonary clues to the presence of a disease process. It is important to emphasize that pulmonary disorders, whether acute or chronic, may originate in the lung or secondarily involve the lung after originating in another part of the body. Diagnostic testing supplements the medical history and physical examination. A wide range of diagnostic tests is now available to help the physician diagnose a specific respiratory system disease correctly.

There are hundreds of different chronic respiratory diseases. Table 1 provides an outline of their major headings and a few important examples of each category. The list is not intended to be complete, and the reader is referred to medical textbooks or electronic sources for a more complete listing. The remainder of this section will address briefly a few of the most important chronic respiratory diseases.

COPD. Chronic obstructive pulmonary disease is the most important and common of the chronic respiratory diseases. Remarkably, few Americans know what COPD is. This condition has been defined as "a disease state characterized by the presence of airflow obstruction due to chronic bronchitis or emphysema; the airflow obstruction is generally progressive, may be accompanied by airway hyperreactivity, and may be partially reversible" (American Thoracic Society, 1995). Most patients with COPD have smoked at least one pack of cigarettes daily for twenty years or longer. By their fifth or sixth decade of life they suffer from dyspnea, productive cough (often worse in the morning), difficulty in clearing sputum from the airways, wheezing, or any combination of these symptoms. Slowly and gradually the symptoms progress year by year and are often mistakenly attributed to increasing age or to another disease such as asthma. Initially, the dyspnea occurs only with extreme exertion, but eventually, in severe cases, it limits simple activities such as changing clothes, raising the arms above the head, bending over, or taking a shower. The diagnosis of COPD may be made by the medical history, physical examination, pulmonary function tests, and a chest X-ray, after exclusion of other conditions such as asthma, bronchiectasis, lung cancer, and congestive heart failur.

Essential steps in managing COPD are outlined in Table 2. Smoking cessation slows the agerelated rate of loss of pulmonary function in middle-aged smokers with mild COPD. In COPD patients with low blood oxygen levels (hypoxemia), continuous oxygen therapy prolongs survival. All other treatment approaches are aimed at improving symptoms. No treatment intervention restores lung function to normal. Intense rehabilitation of patients with severe COPD provides temporary improvement in symptoms. Surgical treatment options are limited to a very small fraction of COPD patients and outcome benefits are the focus of ongoing research. Without treatment, COPD pursues a downhill course leading to premature disability and death.

Cancer. Cancer represents another broad category of chronic respiratory disease. Cancer may affect any part of the respiratory tract, including the larynx. Cancer that involves the lung is called "primary" if it originates in the lung and "secondary" if it spreads to the lung from another site. Primary lung cancer usually develops from the epithelial lining of the bronchi (bronchogenic carcinoma). Rarely it originates from the lung's soft tissues or the outer lining on the lung's surface (malignant mesothelioma). The layman's term "lung cancer" usually refers to bronchogenic carcinoma, a deadly chronic disease that in about 90 percent of cases is caused by cigarette smoking.

Patients with bronchogenic carcinoma have a wide variety of initial clinical manifestations, but a typical presentation is a new or changing respiratory symptom in combination with an abnormal chest X-ray. Loss of appetite and weight loss are common. Unfortunately, by the time most patients (about 75%) seek medical attention, the lung cancer cannot be entirely removed by surgery (unresectable) because it has spread in the chest or elsewhere in the body (the stage of the cancer is advanced). Or, the patient may be too ill to tolerate chest surgery because of the systemic effects of

Table 1

the cancer or another smoking-related condition such as COPD or heart disease. Anticancer drug therapy (chemotherapy), radiation therapy, and other treatment methods may provide temporary improvement in the size of the cancer (remission), diminution of symptoms (palliation), or slightly improved survival. Nevertheless, cure of lung cancer by nonsurgical approaches is rare, and most patients with unresected lung cancer die prematurely from the disease. Overall, only 14 percent of patients with lung cancer survive for five years.

Infiltrative Lung Disease. Another broad category of chronic respiratory disease is infiltrative lung disease, in which shadows (infiltrates) appear in the lung tissue on the standard chest X-ray. Infiltrates are caused by the accumulation of cells or fluids in parts of the lung in excess of their normal amount. Infiltrates may be localized (focal) or widespread (diffuse—involving all five lobes of the lung). They may involve the lung's tissue framework ("interstitial" infiltrate), airspace ("alveolar" infiltrate), or both. Well over one hundred specific lung diseases fall into the category of infiltrative disease, which may be acute or chronic; many of them are occupational in origin. The chronic infiltrative diseases share many similar findings, among which are unrelenting dyspnea (sometimes with a dry cough); abnormal lung sounds (crackles) on chest physical examination; reduced amount of air in the lung (restrictive dysfunction) and reduced gas transfer (diffusing capacity) on pulmonary function testing; and hypoxemia, especially with exercise.

Idiopathic Pulmonary Fibrosis (IPF). A lung scarring of unknown cause, IPF is the prototype of the chronic infiltrative pulmonary diseases, just as COPD is the prototype of the chronic airway diseases. IPF affects men and women between the ages of fifty and seventy. The prevalence of IPF has been estimated to be three to six cases per 100,000 people. Although the exact cause of this disease is not known, cigarette smoking is a suspected risk factor. Progressive dyspnea, dry cough, and crackles on physical examination are typical clinical features of this disease. Patients with suspected IPF are often evaluated with high-resolution computed tomography (HRCT) imaging, which displays patchy scarring below the lung surface, especially in the lower lung zones. Biopsy of lung tissue via the airway (flexible fiberoptic bronchoscopy)

Table 2

or via the chest wall (video-assisted thoracic surgery) is often employed to confirm the clinical impression. Treatment of this condition is mainly supportive, as the scarring itself is not reversible. Continuous supplemental oxygen is helpful in reducing dyspnea. Anti-inflammatory therapy with corticosteroids or immunosuppressive agents is frequently attempted, but results are usually disappointing. Treatment with interferon has been investigated. Lung transplantation is an option for a few patients with IPF. Most patients with IPF have a poor prognosis, and median survival is about five years.

Ventilatory Control Disorders. The rate, depth, and rhythm of normal breathing are exquisitely controlled by a complex interplay of regulatory mechanisms in the brain, the respiratory system, the great blood vessels, and other parts of the body. Disturbances in any of these mechanisms may lead to altered breathing (ventilatory) control, sometimes with disastrous consequences. A number of chronic respiratory disorders may be attributed to abnormal control of ventilation, including sleep apnea and obesity-hypoventilation syndrome.

The most common and important disorder of ventilatory control is sleep apnea syndrome. An apnea is defined as cessation of airflow at the nose and mouth for more than ten seconds, and an hypopnea is a drop of oxyhemoglobin saturation of more than 4 percent with reduced air-flow. Obstructive apneas occur because of temporary closure of the throat (pharynx) and central apneas occur because of a transient reduction in breathing effort. The consequences of apneas and hypopneas during sleep are nocturnal hypoxemia and poor sleep quality. Sleep apnea is confirmed by performing recordings of physiological variables during sleep (polysomnography). An excessive number of apneas and hypopneas during a night of sleep defines sleep apnea. Sleep apnea syndrome is present when sleep apnea is accompanied by associated symptoms, including loud and cyclical snoring, excessive daytime sleepiness and daytime sleep attacks, morning sluggishness, daytime fatigue or tiredness, neuropsychological impairment, and declines in personality.

Obstructive sleep apnea is very prevalent, being found in 24 percent of middle-aged men and 9 percent of middle-aged women. Obstructive sleep apnea syndrome (OSAS) occurs in 4 percent of men and 2 percent of women. Overweight middle-aged and older men are most commonly affected. Hypoxemia during sleep and sleep disruption may be so severe as to cause daytime problems, particularly excessive and inappropriate sleepiness. Patients with OSAS may fall asleep while driving a car, operating machinery, or performing a job. Substantial psychosocial consequences may follow, including personality changes, marital stress, and loss of employment. The medical consequences of OSAS include high blood pressure in the lung (pulmonary hypertension), and in the body as a whole (systemic hypertension); failure of the right side of the heart; heart rhythm disturbances; and cardiovascular complications (stroke, myocardial infarction, and sudden death).

Treatment of OSAS consists of general measures such as patient education, weight loss, avoidance of alcohol and hypnotic medication, surgical relief of mechanical upper airway obstruction, and improved sleep habits. Many patients with OSAS are treated with nocturnal use of nasal continuous positive airway pressure (nasal CPAP) masks that stent the airway open during sleep, precluding pharyngeal obstruction. Dramatic improvement in symptoms is commonly observed. Results of treatment of central sleep apnea syndrome are less encouraging.

Obesity hypoventilation ("Pickwickian") syndrome is a disorder of ventilatory control in patients with moderate to severe obesity. This condition is thought to be caused by blunted breathing effort (ventilatory drive) and the mechanical load placed on the chest wall and abdomen by obesity. This disorder occurs in only a small percent of patients with obesity. The daytime hypoxemia and elevated blood carbon dioxide levels (hypercapnia) found in this condition may improve with significant weight loss. Patients with this condition also suffer from OSAS.

In conclusion, chronic respiratory diseases are very prevalent in our society. They cause untold suffering, premature death, and economic harm to patients, their families, and the nation. Chronic obstructive pulmonary disease, lung cancer, idiopathic pulmonary fibrosis, and obstructive sleep apnea syndrome are common examples of these chronic respiratory diseases. Treatment for these conditions is difficult and expensive, but successful management provides substantial symptomatic benefit for most patients. Many of the chronic respiratory diseases could be prevented by elimination of cigarette smoking.

JOHN L. STAUFFER

(SEE ALSO: Asthma; Bronchitis; Lung Cancer; Occupational Lung Disease; Pulmonary Function; Smoking Behavior; Smoking Cessation; Tobacco Control)

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