Crackles have two leading explanations. (1) They result from a series of tiny explosions when small airways, deflated during expiration, pop open during inspiration. This mechanism probably explains the late inspiratory crackles of interstitial lung disease and early congestive heart failure. (2) Crackles result from air bubbles flowing through secretions or lightly closed airways during respiration. This mechanism probably explains at least some coarse crackles.
Late inspiratory crackles may begin in the first half of inspiration but must continue into late inspiration. They are usually fine and fairly profuse, and persist from breath to breath. These crackles appear first at the bases of the lungs, spread upward as the condition worsens, and shift to dependent regions with changes in posture. Causes include interstitial lung disease (such as fibrosis) and early congestive heart failure.
Early inspiratory crackles appear soon after the start of inspiration and do not continue into late inspiration. They are often but not always coarse and are relatively few in number. Expiratory crackles are sometimes associated. Causes include chronic bronchitis and asthma.
Inspiration Expiration d_l
Wheezes and Rhonchi
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.