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Exhalation (or expiration) is the flow of the breath out of an organism. In animals, it is the movement of air from the lungs out of the airways , to the external environment during breathing . This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume.
However, in a normal mammal, the lungs cannot be emptied completely. In an adult human, there is always still at least one liter of residual air left in the lungs after maximum exhalation. [8] Diaphragmatic breathing causes the abdomen to rhythmically bulge out and fall back. It is, therefore, often referred to as "abdominal breathing".
Crackles are caused by the "popping open" of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration. Crackles can be heard in people who have pneumonia , atelectasis , pulmonary fibrosis , acute bronchitis , bronchiectasis , acute respiratory distress syndrome (ARDS), interstitial lung disease or post ...
The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. The elasticity of these muscles is crucial to the health of the respiratory system ...
The normal relaxed state of the lung and chest is partially empty. Further exhalation requires muscular work. Inhalation is an active process requiring work. [4] Some of this work is to overcome frictional resistance to flow, and part is used to deform elastic tissues, and is stored as potential energy, which is recovered during the passive process of exhalation, Tidal breathing is breathing ...
The alveolar air pressure is therefore always close to atmospheric air pressure (about 100 kPa at sea level) at rest, with the pressure gradients because of lungs contraction and expansion cause air to move in and out of the lungs during breathing rarely exceeding 2–3 kPa. [18] [19] During exhalation, the diaphragm and intercostal muscles relax.
Ventilation is normally unconscious and automatic, but can be overridden by conscious alternative patterns. [3] Thus the emotions can cause yawning, laughing, sighing (etc.), social communication causes speech, song and whistling, while entirely voluntary overrides are used to blow out candles, and breath holding (for instance, to swim underwater).
Airway resistance can also vary between inspiration and expiration: In emphysema there is destruction of the elastic tissue of the lungs which help hold the small airways open. Therefore, during expiration, particularly forced expiration, these airways may collapse causing increased airway resistance.