Lung Diseases

The lungs are part of the respiratory (breathing) system and are located in the chest, inside the rib cage and above the diaphragm. Lungs are complex organs that consist of spongy, elastic tissue equipped with structures that infuse our blood with fresh oxygen while ridding it of carbon dioxide

Oxygen enters the lungs when we inhale a breath. It is distributed throughout the lungs by a system called the bronchial tree, with branches of decreasing diameter (called bronchi and bronchioles). The bronchial tree carries air to small sacs (alveoli) deep within the lung where oxygen from air moves from the lung into the bloodstream, and carbon dioxide, a byproduct of metabolism, moves from the blood into the lung to be exhaled. Intake of oxygen and delivery by the blood to tissue is necessary for all of the cells in our body to function. Removal of carbon dioxide is necessary to maintain the blood's pH at an appropriate level as part of the body's system of acid-base balance.

Since the air we breathe contains many components from the environment such as dust, pollens, bacteria, viruses, smoke, and harmful chemicals, the lungs maintain a system of defense against these potentially toxic invaders. The lungs' defense system includes immune cells and the secretion of mucus to contain and remove these unwanted components from the lungs.

Common lung diseases include:

Asthma is a chronic lung disease characterized by inflammation of the bronchi and bronchioles and episodes of airway obstruction. During an attack, the lining of the airways swell and the muscles surrounding the bronchi contract, narrowing the airway. Mucus secretion can further inhibit the flow of air, making breathing difficult and causing the affected person to wheeze. Most episodes do not cause permanent lung damage but frequently require immediate medical attention since lack of oxygen and build-up of carbon dioxide can be life-threatening. People with asthma are sensitive to a variety of substances that do not cause the same reaction in other people. Episodes may be triggered by cold air, exercise, cigarette smoke, or other particles in the air such as dust, mold, or allergens. The triggers for each person may be different. According to the American Lung Association (ALA), asthma is the most common chronic disorder in childhood. The number of people with asthma continues to grow with about 25 million Americans being affected as of 2009. It is estimated that 1 in 10 children have asthma.

Chronic obstructive pulmonary disease (COPD) is a term used for both emphysema and chronic bronchitis. According to the ALA, COPD is the third leading cause of death in the United States. With chronic bronchitis, the bronchial tubes become inflamed and scarred. With emphysema, the air sacs in the lungs are slowly destroyed. With both disorders, those affected experience increasing difficulty exhaling and getting a sufficient oxygen supply. Smoking causes about 85-90% of the deaths associated with COPD. Other risk factors include repeated exposure to air pollution.

Pulmonary fibrosis is a lung disease characterized by damage and scarring to the tissues of the lungs, including those between and supporting the air sacs. In many cases, the cause of the inflammation and stiffening is unknown but may include:

• Occupational or environmental exposure to small particles, including repeated exposure to inorganic substances such as asbestos, coal, beryllium, and silica
• Repeated exposure to organic substances such as moldy hay, animal droppings, and grain dust that causes hypersensitivity pneumonitis, an allergic reaction, that eventually leads to pulmonary fibrosis
• Chemicals and drugs that are toxic to the lungs
• Previous radiation treatment
• Sarcoidosis
• Scleroderma and other autoimmune disorders
• Unknown (idiopathic)

Infections can occur primarily in the lungs, may affect the entire body, including the lungs, or may develop in the pleura, which are the membranes surrounding the lungs. They may be acute or chronic and be caused by bacteria, viruses, and more rarely, fungi.

• Pneumonia is an acute lung tissue inflammation caused by a variety of microorganisms.
• Influenza is an acute illness caused by a virus that includes respiratory symptoms.
• Tuberculosis and nontuberculous mycobacteria (NTM) are chronic infections most commonly seen in people with weakened immune systems (such as those with HIV/AIDS). The infections caused by mycobacteria develop slowly and can be confined to the lungs or affect the body as a whole (systemic).

Lung cancer is the uncontrolled growth of malignant cells that originate in the lungs. There are two main types, small cell and non-small cell lung cancers. Other cancers may spread to the lungs but are not considered lung cancer and are treated differently. The number of lung cancer deaths has been rising in women in recent years and falling in men. According to the ALA, lung cancer is currently the leading cause of cancer death for American women and men, killing more people than the next three most common cancers (colon, breast, and prostate) combined. Risks for lung cancer include smoking and exposure to radon.

Pulmonary hypertension is a lung disorder characterized by a narrowing of the blood vessels in the lungs, increasing their blood pressure and causing the heart to work harder to transport blood into the lungs. This condition may co-exist and worsen a variety of lung diseases and can lead to heart failure.

Pulmonary embolism is a blood clot that usually originates in the veins of the legs or pelvis and travels to the lungs, where it blocks a blood vessel, causing chest pain, acute shortness of breath, and coughing. This condition can be life-threatening and requires prompt medical attention.

Bronchopulmonary dysplasia (BPD) is a lung disease that develops primarily in premature infants who have undergone prolonged oxygen therapy and/or have been on mechanical ventilation for extended periods of time but may also be seen in those who have experienced oxygen toxicity or had pneumonia. With this disorder, airways are inflamed, do not develop normally, and may be damaged.

Respiratory distress syndrome (RDS) of the newborn is a life-threatening breathing problem that may develop in infants born earlier than 6 weeks before their due date. These premature babies' lungs are not able to produce an adequate amount of the protective liquid substance called surfactant. Without sufficient surfactant, the lungs are not able to expand or inflate properly and the babies have difficulty breathing in enough oxygen. It is a condition that may occur within a few hours after a premature birth.

Acute respiratory distress syndrome (ARDS) is the rapid onset of severe breathing difficulties due to extensive lung inflammation and the lungs filling with fluid. It is a sometimes fatal condition that can be brought on by many types of injury to the lungs, including serious viral or bacterial infection, sepsis, trauma, multiple blood transfusions, drug overdose, or inhalation of substances such as salt water or smoke.

Cystic fibrosis is an inherited disease that affects the lungs, pancreas, and other body systems. It is characterized by salty sweat, the production of thick mucus that can obstruct breathing, and a decreased ability to digest fats and proteins, leading to malabsorption and malnutrition. It is more common in Caucasians than other ethnic groups and is usually diagnosed in infancy. According to the ALA, about 1,000 new cases are diagnosed in the U.S. each year.

Alpha-1 antitrypsin deficiency is an inherited deficiency of a protein that provides protection to the lungs. Without this protection, the lungs become progressively damaged and the person is at a significantly increased risk of developing early-onset emphysema and liver disease. The ALA estimates that about 100,000 Americans have this deficiency, and about 20 million are genetic carriers of the disease.

Other disorders do not affect the lungs directly, but they impair a person's ability to breathe properly. These extrinsic disorders may affect the chest cavity, muscles, nerves, and heart. They include a variety of conditions, such as neuromuscular diseases like muscular dystrophy, polio, myasthenia gravis, Guillain-Barré syndrome, and amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease), and disorders that result in abnormal spine formation or rib cage movement, which can restrict lung expansion. [Specific testing and treatment for these extrinsic disorders are not covered in this article.]

Signs and symptoms associated with lung disease will vary from person to person and change over time. With chronic conditions, symptoms often emerge gradually and grow progressively worse. With acute conditions, symptoms may be mild to severe. Some may be life-threatening without prompt medical attention. While each disease will have its own characteristics, there are common signs and symptoms that are seen with many lung disorders. Examples include:

• Persistent cough and shortness of breath or labored breathing (dyspnea)
• Wheezing, gasping for breath 
• Coughing up mucus, blood or sputum
• Chest pain
• People with obstructive lung conditions such as COPD may have trouble exhaling; some describe it as "like trying to breathe through a straw."
• Lack of oxygen may cause an affected person's skin to have a bluish tint.
• Over time, oxygen deficiency may lead to clubbing in some people, an enlargement of the fingertips and abnormal fingernail growth.

The goals of testing are to diagnose lung diseases, determine their causes where possible, and evaluate their severity. Many health practitioners will order blood gases to evaluate oxygen and carbon dioxide levels, lung or pulmonary function tests (PFTs) to help diagnose and monitor lung function, and chest x-rays and or CT (computed tomography) scans to look at lung structure. Other testing is performed to help diagnose specific conditions.

Laboratory tests

Some tests may be performed to help determine a person's health status and how well the lungs are working. Examples include:

• Blood gases – a blood sample collected from an artery is used to evaluate blood pH, oxygen and carbon dioxide
• Complete blood count (CBC) – to evaluate blood cells and check for anemia
• Comprehensive metabolic panel (CMP) – to evaluate organ function and chemical and electrolyte balances

Additional tests may be performed to help diagnose certain lung conditions:

• Cystic fibrosis tests
  • CF gene mutation testing – to look for the genetic mutations that cause cystic fibrosis
  • Sweat chloride
  • Immunoreactive trypsin (IRT)
  • Stool trypsin
• Alpha-1 antitrypsin – to determine if a person has AAT deficiency
• Pleural fluid analysis – to investigate the cause of fluid accumulation between the chest wall and the outside of each lung; it may be due to, for example, cancer or infections.
• Allergy tests – may be ordered to determine asthma triggers
• Tests for pneumonia or other specific infections:
  • Bacterial sputum culture and Gram stain – to diagnose lung infections caused by bacteria or fungi
  • AFB testing – to diagnose tuberculosis or a nontuberculous mycobacteria (NTM) infection
  • Blood cultures – to diagnose bacteria and sometimes yeast infections that have spread into the blood
  • Influenza tests – to diagnose influenza (flu)
  • Respiratory syncytial virus (RSV)
  • Pertussis – to diagnose whooping cough
  • Fungal tests
  • Mycoplasma tests
  • Legionella tests
• Tests for autoantibodies may help determine if an autoimmune disorder is affecting the lungs:
  • Anti-nuclear antibody (ANA)
  • Extractable nuclear antigen (ENA) panel
  • Anti-ds DNA
• Lung biopsy – to evaluate lung tissue for damage or for cancer (see the article on Anatomic Pathology for more on this)
• Lung cancer tests for targeted therapy – the following tests may be performed on biopsy samples to help determine whether treatments that target certain types of lung cancer will be effective:
  • EGFR gene mutation – if present, a person is more likely to respond to tyrosine kinase inhibitor drug therapies such as gefitinib and erlotinib.
  • KRAS gene mutation – if present, a person is less likely to respond to tyrosine kinase inhibitors.
  • ALK gene mutation / gene rearrangement (EML4-ALK) – if a mutation is present, the cancer is more likely to respond to ALK kinase inhibitors such as crizotinib and less likely to respond to tyrosine kinase inhibitors.
  • ROS1 gene mutation – those with gene rearrangement are more likely to respond to crizotinib and less likely to respond to tyrosine kinase inhibitors.
• Sputum cytology – to evaluate lung cells for abnormal changes or for cancer
• Soluble mesothelin-related peptides (SMRP) – to monitor mesothelioma, a specific type of lung cancer
• Drug screen – to detect drugs in overdoses that can lead to decreased respiration or acute respiratory distress
• Fetal lung maturity (FLM) tests – used to evaluate the lung maturity of a fetus and may include tests for lecithin/sphingomyelin (L/S) ratio, phosphatidylglycerol (PG), foam stability index (FSI), or lamellar body counts (LBC); may be used to determine age of gestation before cesarean delivery or when a preganant woman is having symptoms of premature labor.

Lung function tests (pulmonary function tests, PFT)
A few of the more common tests are listed below. For more complete information, visit the web site for Johns Hopkins Medicine: Pulmonary Function Laboratory.

• Spirometry – measures the amount and rate of air exhalation as a person blows out through a tube; it is performed to evaluate narrowed or obstructed airways.
• Oximetry – measures the oxygen saturation of the blood using a small device placed on a person's finger
• Exercise stress test – monitors lung function on a person while they are on a stationary bike or treadmill
• Air flow with a peak flow meter – measures the rate of exhalation; it can be used at home by people with asthma to help monitor their condition.
• Lung volume – the quantity of air a person takes into their lungs and how much is left in the lungs after exhalation; it helps evaluate the elasticity of the lungs, the movement of the rib cage, and the strength of the muscles associated with respiration.
• Diffusing capacity measurement – assesses the transfer of oxygen from the lung air sacs to the bloodstream by evaluating how much carbon monoxide is absorbed when a small quantity is inhaled (not enough to harm)

Imaging studies

• Chest x-ray – to look at lung structure and chest cavity
• CT (computed tomography) scan – a more detailed evaluation of lung structure
• MRI (Magnetic resonance imaging) – detailed pictures of organs and vessels in the chest
• Ultrasound – used to detect fluid between the pleural membranes
• Nuclear lung scanning – used to help detect pulmonary embolism and, rarely, to evaluate the effectiveness of lung cancer treatment
• Positron emission tomography (PET) scans – used to help diagnose lung cancer

For more on these, see the RadiologyInfo.org website.

Other tests

• Electrocardiogram (EKG, ECG) – to look at heart rhythm, to determine if heart disease may be affecting breathing
• Sleep studies – usually performed at special sleep centers to help determine whether a person is breathing normally during sleep

The goals of lung disease treatment are to prevent the disease wherever possible, treat infections and prevent their spread to other people, reduce inflammation, stop or slow the progression of lung damage, relieve symptoms, ease breathing, minimize the side effects associated with some treatments, and make sure that the affected person is getting sufficient oxygen.

Many cases of lung disease could be prevented by not smoking, testing for radon, minimizing exposure to particulates such as asbestos, coal, beryllium, silica, molds, grain dust, air pollution, and to chemicals and drugs known to affect the lungs.

People with weakened immune systems, existing lung disease, and those who are very young or elderly should talk to their health practitioner about the advisability of getting annual flu shots and pneumococcal vaccines to minimize their risk of getting influenza and pneumonia.

New therapies for lung diseases continue to be developed and people's treatment needs change over time. Those who have been diagnosed and are living with lung disease should talk to their health practitioners periodically about the treatments that are right for them.