Expiration is the medical term for a phase of the respiratory cycle, more specifically the process of breathing out, which involves forcing air out of the lungs. This is usually a passive process of the body caused by the relaxation of the diaphragm as well as the chest muscles.
What is expiration?
Expiration is the medical term for a phase of the respiratory cycle, more specifically the process of breathing out, during which air is forced out of the lungs. Expiration is a phase of the respiratory cycle that is completed by inspiration and several intermediate phases. Expiration refers to the process of breathing out. At rest, this process occurs passively. The goal of expiration is to push stale air out of the lungs so that fresh, oxygen-rich air can subsequently flow in. The diaphragm and chest muscles automatically relax during exhalation, forcing much of the inhaled air back out of the lungs. However, expiration can also be voluntary. In this case, the muscles of the respiratory musculature as well as the auxiliary respiratory musculature are used consciously. In both variants, some air remains in the lungs, but it can still be exhaled by consciously using the respiratory muscles. The amount of air remaining in the lungs during passive exhalation is called end-expiratory lung volume.
Function and purpose
The goal of expiration is to move air that is rich in carbon dioxide and low in oxygen out of the lungs to make room for fresh and oxygen-rich air. Passive relaxation of the diaphragm and respiratory muscles reduces the size of the chest and, with it, the lungs. This creates a higher pressure in the lungs compared to the air in the environment, causing the stale air to flow out. If the air has flowed out, on the other hand, there is negative pressure in the lungs. Due to this condition, fresh, oxygen-rich air can flow back into the lungs in the course of inspiration. If the diaphragm relaxes, it is pressed upward and thus against the lungs. This causes the lungs to be compressed. This process is assisted by the respiratory muscles, medically known as the intercostal muscles. The intercostal muscles include the outer and inner intercostal muscles. The outer intercostal muscles relax just before expiration, while the inner ones tighten. This causes the chest to contract and exerts slight pressure on the lungs, causing them to shrink as well. Visually, this is visible by a lowering of the rib cage. Both muscles or muscle groups are supported in their function by the respiratory support muscles. These also contract the rib cage and press the diaphragm upward against the lungs, thus supporting the expiratory phase. However, the muscles of the expiratory support musculature are not located in close proximity to the lungs and thus do not directly affect the process of exhalation. Exhalation support muscles include the abdominal press, a part of the abdominal musculature that is also used during coughing or sneezing and during defecation, the spinal erector (Musculus errector spinae), and the long back muscle (Musculus latissimus dorsi).
Diseases and ailments
Expiration can be complicated by various diseases of the respiratory system. Most commonly, obstructive lung diseases prevent trouble-free expiration. Obstructive pulmonary disorders are characterized by narrowing or obstruction of the airways, making exhalation difficult and slowed. About 90 percent of all lung diseases are of this type. In the case of obstructive lung diseases, the air that is breathed often still flows into the lungs without any problems, but cannot then flow out again unhindered, which means that the lungs quickly become overinflated. This is often due to a narrowing of the lower airways, the bronchi. If, on the other hand, the upper airways in the area of the larynx are narrowed, not enough air flows into the lungs in the first place. Obstructive lung or airway disease can quickly become chronic. It usually begins as chronic bronchitis, which is accompanied by coughing, sputum, shortness of breath and reduced performance, or as emphysema, in which the lungs are chronically overinflated. Both conditions usually result from inhalation of pollutants or smoking. However, genetic predispositions also frequently exist for emphysema.Asthma, stenosis of the bronchial tree, glottic edema, tumors or foreign bodies in the airways can also cause obstructive disorders of the lungs. The second major group of lung diseases are restrictive disorders. Such disorders restrict the expansibility of the lungs and thus reduce the exchange volume of air. As a result, part of the lung is either still ventilated but no longer supplied with blood, as is the case with pulmonary embolism. Or it is still supplied with blood but no longer adequately ventilated, which is the case with bronchial obstruction. In both variants, the blood in the lungs can no longer be adequately oxygenated. The causes of restrictive lung disorders can be varied. They often result from pneumonia, pulmonary edema or fibrosis, inflammation or air trapping in the pleura, general diseases of the respiratory muscles, or injuries and deformities in the chest area. The most common variants of restrictive lung disorders are pulmonary fibrosis, a chronic and progressive inflammation of the lung tissue, and asbestosis, which results from exposure to asbestos fibers, usually occupational and for too long.
