Crackles, crepitations, or rales are the clicking, rattling, or crackling noises that may be made by one or both lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s of a human

Human

Humans are the only living species in the Homo genus...

 with a respiratory disease

Respiratory disease

Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange possible in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the...

 during inhalation

Inhalation

Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....

. They are often heard only with a stethoscope

Stethoscope

The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

 ("on auscultation

Auscultation

Auscultation is the term for listening to the internal sounds of the body, usually using a stethoscope...

"). Bilateral crackles refers to the presence of crackles in both lungs.

Basal or basilar crackles (not to be confused with the basilar artery

Basilar artery

In human anatomy, the basilar artery is one of the arteries that supplies the brain with oxygen-rich blood.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with...

 of the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

) are crackles apparently originating in or near the base of the lung. Bibasal or bibasilar crackles refer to crackles at the bases both the left and right lungs. Bilateral basal crackles also refers to the presence of basal crackles in both lungs.

Crackles are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration. The word "rales" derives from the French word râle meaning "rattle".

Crackles can be heard in patients with pneumonia

Pneumonia

Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

, atelectasis

Atelectasis

Atelectasis is defined as the collapse or closure of alveoli resulting in reduced or absent gas exchange. It may affect part or all of one lung. It is a condition where the alveoli are deflated, as distinct from pulmonary consolidation.It is a very common finding in chest x-rays and other...

, pulmonary fibrosis

Pulmonary fibrosis

Pulmonary fibrosis is the formation or development of excess fibrous connective tissue in the lungs. It is also described as "scarring of the lung".-Symptoms:Symptoms of pulmonary fibrosis are mainly:...

, acute bronchitis

Bronchitis

Acute bronchitis is an inflammation of the large bronchi in the lungs that is usually caused by viruses or bacteria and may last several days or weeks. Characteristic symptoms include cough, sputum production, and shortness of breath and wheezing related to the obstruction of the inflamed airways...

, or bronchiectasis

Bronchiectasis

Bronchiectasis is a disease state defined by localized, irreversible dilation of part of the bronchial tree caused by destruction of the muscle and elastic tissue. It is classified as an obstructive lung disease, along with emphysema, bronchitis, asthma, and cystic fibrosis...

. Pulmonary edema

Pulmonary edema

Pulmonary edema , or oedema , is fluid accumulation in the air spaces and parenchyma of the lungs. It leads to impaired gas exchange and may cause respiratory failure...

 secondary to left-sided congestive heart failure

Congestive heart failure

Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...

 can also cause rales.

Terminology

The terms rales and crepitations are both still in common use in the US but less common elsewhere. Use of the term rales has been discouraged by the American Thoracic Society

American Thoracic Society

American Thoracic Society , established in 1905, is an independently incorporated, international, educational and scientific society, serving its 18,000 members worldwide who are dedicated in respiratory and critical care medicine...

 and American College of Chest Physicians

American College of Chest Physicians

The American College of Chest Physicians is a medical organization in the United States consisting of physicians and non-physician specialists in the field of chest medicine, which includes pulmonology, thoracic surgery, and critical care medicine....

 since 1977, by numerous authors, and this is enforced by the editorial policy of a number of major medical journals.

In Sweden, crepitations refer specifically to fine, dry crackles.

The sound of crackles

Crackles are caused by explosive opening of small airways and are discontinuous, nonmusical, and brief. Crackles are much more common during the inspiratory than the expiratory phase of breathing, but they may be heard during the expiratory phase. Crackles are often associated with inflammation or infection of the small bronchi, bronchioles, and alveoli. Crackles that don't clear after a cough may indicate pulmonary edema or fluid in the alveoli due to heart failure or acute respiratory distress syndrome

Acute respiratory distress syndrome

Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....

.

• Crackles are often described as fine, medium, and coarse. They can also be characterized as to their timing: fine crackles are usually late-inspiratory, whereas coarse crackles are early inspiratory.

• Fine crackles are soft, high-pitched, and very brief. This sound can be simulated by rolling a strand of hair between one's fingers near the ears, or by moistening one's thumb and index finger and separating them near the ears. Their presence usually indicates an interstitial process, such as pulmonary fibrosis or congestive heart failure.

• Coarse crackles are somewhat louder, lower in pitch, and last longer than fine crackles. They have been described as sounding like opening a Velcro
  Velcro
  Velcro is the brand name of the first commercially marketed fabric hook-and-loop fastener, invented in 1948 by the Swiss electrical engineer George de Mestral...
  
  fastener. Their presence usually indicates an airway disease, such as bronchiectasis.

They can also be described as unilateral or bilateral, as well as dry or moist/wet.

Crackles can be heard over the lower lobe of the lungs. Pulmonary edema makes it much more audible.