A pleural friction rub, or simply pleural rub, is a medical sign

Medical sign

A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....

, audible by listening to the internal sounds of the body, usually using 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 the lungs, that is used in the diagnosis

Diagnosis

Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

 of pleurisy

Pleurisy

Pleurisy is an inflammation of the pleura, the lining of the pleural cavity surrounding the lungs. Among other things, infections are the most common cause of pleurisy....

 and other conditions affecting the chest cavity.

Pleural friction rubs are the squeaking or grating sounds of the pleural linings rubbing together and can be described as the sound made by treading on fresh snow. They occur where the pleural layers are inflamed and have lost their lubrication. Pleural rubs are common in 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...

, pulmonary embolism

Pulmonary embolism

Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...

, and pleurisy (pleuritis). Because these sounds occur whenever the patient's chest wall moves, they appear on inspiration

Inhalation

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

 and expiration

Exhalation

Exhalation is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing....

.