Lung diseases



Last Review Date: November 6, 2017


Overview of the lungs

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 that is designed to take in oxygen and get rid 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, which has branches of decreasing diameter (called bronchi and bronchioles). The bronchial tree carries oxygen to small sacs (alveoli) deep within the lung where oxygen (taken from the air that is inhaled) moves from the lung into the blood stream, and carbon dioxide (a by-product of our metabolism) moves from the blood into the lung to be exhaled. Taking in oxygen, and delivering that oxygen (via the blood) to the tissues is necessary for all of the cells in our body to function. The 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 volatile chemicals), the lungs maintain a system of defence against these potentially toxic invaders. The lungs’ defence system relies on immune cells and the secretion of mucus, both of which contain and remove these unwanted components from the lungs.


Lung diseases

Lung diseases are conditions in which some function of the lung is adversely affected. In some cases, the problem lies in the gas exchange process that takes place in the membrane between the alveoli and the blood; this impedes the efficient uptake of oxygen and removal of carbon dioxide. In other cases, the problem is the inability of the bronchial system to effectively deliver air to the alveoli, possibly due to a blockage in the branches of the bronchial tree or because the chest muscles are not expanding and contracting enough to move air through the bronchial tree to the alveoli. Sometimes the problem is the lung's inability to remove or detoxify foreign substances, possibly because of an underlying deficiency or because the sheer quantity of these substances has overwhelmed the lungs’ defence systems.

Common lung diseases include:

Asthma is a chronic lung disease characterised by inflammation of the bronchi and bronchioles and episodes (attacks) of airway obstruction. 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 cigarette smoke and other particles in the air, dust, mould, allergens, exercise, cold air and other factors. The triggers for each person may be different. During an attack, the lining of the airways swells and the muscles surrounding the bronchi contract, narrowing the airway. Mucus secretion can further inhibit the flow of air, which makes breathing difficult and causes the affected person to wheeze. Most episodes do not cause permanent lung damage but they frequently require immediate medical attention because the lack of oxygen and the build-up of carbon dioxide can be life threatening. According to the Asthma Foundation of Queensland, asthma is the most common chronic disorder in childhood. It affects more than 2.2 million Australians which equates to 1 in 6 children and 1 in 9 adults.

Chronic obstructive pulmonary disease (COPD) is a term used for both emphysema and chronic bronchitis. According to the Australian Lung Association, COPD is the fourth leading cause of death in Australia. With chronic bronchitis, the bronchial tubes become inflamed and scarred. With emphysema, the air sacs in the lungs are slowly destroyed. With both disorders, patients find it increasingly difficult to exhale and to get sufficient oxygen when inhaling. Smoking causes about 80 to 90 percent of the deaths associated with COPD. Other risk factors include repeated exposure to air pollution.

Pulmonary fibrosis is an interstitial (space between) lung disease. This means that it causes damage and scarring to the tissues between the air sacs, inflammation of the air sacs, and stiffening of the lungs. Causes of pulmonary fibrosis 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 mouldy hay, animal droppings and grain dust can cause hypersensitivity pneumonitis and can eventually lead to pulmonary fibrosis
  • Chemicals and drugs that are toxic to the lungs
  • Previous radiation treatment
  • Sarcoidosis
  • Systemic sclerosis and other autoimmune disorders
  • It can also be idiopathic (meaning the cause is unknown)

Infections can occur primarily in the lungs, develop in the pleura (the membranes surrounding the lungs), or affect the entire body (including the lungs). They may be acute or chronic and they can 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 systemic illness that is caused by a virus and includes respiratory symptoms. Tuberculosis and nontuberculous mycobacteria (NTM) are chronic infections most commonly seen in patients with compromised immune systems (such as patients with HIV/AIDS). The infections caused by mycobacteria develop slowly and can be systemic or confined to the lungs.

Lung cancer is the uncontrolled growth of malignant cells in the lungs. There are two main types: small cell and non-small cell lung cancers. Other cancers may spread to the lungs but these are considered metastatic because the cancer cells do not come from lung tissue. The number of lung cancer deaths has been rising in women in recent years and falling in men. According to the Australian Lung Foundation, lung cancer is currently the leading cause of cancer death for Australians overall. Risks for lung cancer include active smoking; passive smoking; occupational exposure to asbestos, steel, nickel, chrome and coal gas processing; and radiation exposure.

Pulmonary hypertension is a lung disorder characterised by a narrowing of the blood vessels in the lungs, which increases their blood pressure and causes the heart to work harder to transport blood into the lungs. This condition may co-exist with (and make worse) a variety of lung diseases and it can lead to heart failure.

A 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 been on mechanical ventilation for extended periods of time, but it 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 developed enough to be able to produce a sufficient amount of a protective liquid substance in the lungs called surfactant. Without 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 of 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 condition that can be fatal. It can be brought on by many types of direct or indirect injury to the lungs, including serious viral or bacterial infection, sepsis, trauma, multiple transfusions, a drug overdose or the 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 characterised 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.

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 patient is at a significantly increased risk of developing early-onset emphysema and liver disease. Over 2,500 people in Australia have a severe alpha-1-antitrypsin deficiency.

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

Signs and symptoms

The signs and symptoms associated with lung disease vary from person to person and change over time. With chronic conditions, symptoms often emerge gradually and grow progressively worse. With acute conditions, symptoms can range from mild to severe. Some may be life threatening without prompt medical attention.

While each disease has its own characteristics, there are common signs and symptoms that are seen with many lung disorders, including a persistent cough and dyspnoea. People may wheeze, gasp, and cough up blood or sputum, and they may experience chest pain. Those with obstructive lung conditions (such as COPD) may have trouble exhaling (some describe it as "like trying to breathe through a straw"). The 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).


Tests

Tests are performed in order to diagnose lung diseases, determine their causes (where possible), and evaluate their severity. Many doctors will order blood gasses 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

Lung function tests (pulmonary function tests, PFT)
A few of the more common tests are listed below. 

  • Spirometry – measures the amount and rate of air exhalation as a patient blows out through a tube. It is performed to evaluate narrowed or obstructed airways.
  • Air flow with a peak flow meter – measures the rate of exhalation. Patients with asthma can use this at home to help monitor their condition.
  • Lung volume – measures 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 – looks at the lung structure and chest cavity
  • CT (computed tomography) scan – enables a more detailed evaluation of the lung structure
  • MRI (magnetic resonance imaging) – provides detailed pictures of the organs and vessels in the chest
  • Ultrasound – detects fluid between the pleural membranes
  • Nuclear lung scanning – helps detect pulmonary embolism and, rarely, is used to evaluate the effectiveness of lung cancer treatment
  • Positron emission tomography (PET) scans – helps diagnose lung cancer

Other tests

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

Treatment

Lung disease treatment aims 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; minimise 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, minimising exposure to particulates (such as asbestos, coal, beryllium, silica, moulds, grain dust, air pollution) and chemicals and drugs known to affect the lungs. People with compromised immune systems or existing lung disease, and those who are very young or elderly, should talk to their doctor about the advisability of getting annual flu injections and pneumococcal vaccines to minimise their risk of getting influenza and pneumonia.

New therapies for lung diseases continue to be developed and patients’ treatment needs change over time. Patients should talk to their doctors periodically about the treatments that are right for them.


Related pages

On this site
Tests: CF gene mutation testing, sweat chloride, immunoreactive trypsin (IRT), stool trypsin, alpha-1 antitrypsin, electrolytes, FBC, AFB smear and culture
Conditions: Cystic fibrosis, tuberculosis, nontuberculous mycobacteria, asthma

Elsewhere on the web
The Australian Lung Foundation
National Asthma Council Australia
Healthdirect Australia: Lung diseases

American Thoracic Society: Patient Information Series (US)
The Lung Association (Canada)

 


Sources

Additional articles used in this review

Greer, Ruari. The temporal evolution of acute respiratory distress syndrome following shock. European Journal of Anaesthesiology. 2010 27(3):226-232

Diaz-Guzman, E., Mannino, D.M. Airway obstructive diseases in older adults: from detection to treatment. Journal of Allergy and Clinical Immunology. 2010 126(4):702-709

Wallis, R.S., Madhukar, P. Menzies, D., Doherty, T.M., Walzl, G., Perkinst, M.D., Zumla, A. Biomarkers and diagnostics for tuberculosis: progress, needs, and translation into practice. Lancet 2010 375(May 29):1920-37.


References from Lab Tests Online-US

Primary sources of information for Lung diseases