Expiration is a process of exhaling outward.
Exhalation belongs to respiratory movements, which are the rhythmic expansion and contraction of the thorax caused by the contraction and diastole of the respiratory muscles. It includes inspiratory and expiratory movements.
During expiratory movement, the thorax becomes smaller, the external intercostal muscles and diaphragm diastole, and the top of the diaphragm lifts up, which is accomplished by the elastic retraction of the alveoli and the thorax, and belongs to the passive process, and the contraction of the internal intercostal muscles occurs during forceful expiration.
Inhalation, on the other hand, is a process of contraction of the diaphragm and external intercostal muscles, and is mainly an inspiratory process.
In addition to this, expiration and inspiration may also use the oblique muscles, sternocleidomastoid muscles, etc., but these muscles are only involved in respiratory movements during forceful breathing.
A common clinical test for expiration is the expiratory test, which is a test that is performed with the help of various types of respiratory muscles to determine respiratory muscle tone, expiratory flow rate, and repetitive respiration, and based on the results of the test to determine whether or not there are respiratory system pathologies. For example, the lung diffusion function is often impaired, and the reduced ventilation function is often seen in insufficient ventilation and reversible narrowing of the airway, which can easily induce dyspnea.