In the mammalian respiratory system, eupnea is normal, good, unlabored breathing, sometimes known as quiet breathing or resting respiratory rate. In eupnea, expiration employs only the elastic recoil of the lungs. Eupnea is the natural breathing in all mammals, including humans. Eupnea does not require any volitional effort whatsoever, but occurs whenever a mammal is in a natural state of relaxation, i.e.
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The word eupnea uses combining forms of eu- + -pnea, from Greek eupnoia, from eu-, "well" + pnoia, "breath". See pronunciation information at dyspnea.
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Animation of diaphragmatic breathing with the diaphragm shown in green Diaphragmatic breathing, or deep breathing, is breathing that is done by contracting the diaphragm, a muscle located horizontally between the thoracic cavity and abdominal cavity. Air enters the lungs, the chest does not rise and the belly expands during this type of breathing. Diaphragmatic breathing is also known scientifically as eupnea, which is a natural and relaxed form of breathing in all mammals. Eupnea occurs in mammals whenever they are in a state of relaxation, i.e.
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The dorsal pons, including the Kolliker-Fuse nucleus and the parabrachial complex, play an important role in respiratory control and rhythm generation. Other areas that aid in breathing control are the cerebellum, neocortex, and the periaqueductal gray (speech and breathing). The generation and modulation of eupnea and the transition between the inspiratory and expiratory phases have also been implicated in respiratory rhythm generation.
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Quiet breathing only requires the activity of the dorsal group which activates the diaphragm, and the external intercostal muscles. Exhalation is passive and relies on the elastic recoil of the lungs. When the metabolic need for oxygen increases, inspiration becomes more forceful and the neurons in the ventral group are activated to bring about forceful exhalation. Shortness of breath is termed dyspnea – the opposite of eupnea.
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There are three phases of the respiratory cycle: inspiration, post-inspiration or passive expiration, and late or active expiration. The number of cycles per minute is the respiratory rate. The respiratory rate is set in the respiratory center by the dorsal respiratory group, in the medulla, and these neurons are mostly concentrated in the solitary nucleus that extends the length of the medulla. The basic rhythm of respiration is that of quiet, restful breathing known as eupnea.
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In eupnea, or normal breathing, the pre-BötC generates a rhythm that is fast and low in amplitude. Sighs, on the other hand, consist of a slow and large amplitude rhythm. Each type of rhythm is generated by the same neurons in the pre-Bötzinger complex, but through different mechanisms, receptors, and ion currents that are controlled by changes in the behavior or environment of the organism. Under low levels of oxygen, the pre-Bötzinger complex needs to rearrange the activity of its neurons and requires the assistance of other brain structures, like the pons, to generate gasping.
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