Eupnea

Eupnea is the normal, quiet, effortless breathing observed at rest in healthy individuals. The term derives from Greek eu- meaning “well” and pnea meaning “breath.” Eupnea describes a regular, unforced pattern of respiration suitable for adequate gas exchange under resting conditions.

Physiology and mechanism: Eupneic breathing is generated by brainstem respiratory centers, including the dorsal respiratory group in the medulla and the pontine centers, with the pre-Bötzinger complex acting as a rhythm generator. Inspiration is primarily active, driven by the diaphragm and intercostal muscles, while expiration is typically passive due to the elastic recoil of the lungs and chest wall. During eupnea, gas exchange is maintained with stable arterial carbon dioxide tension and oxygen saturation.

Characteristics and typical values: In healthy adults at rest, the respiratory rate is about 12–20 breaths per minute, and the tidal volume is around 0.5 liters, yielding a minute ventilation of roughly 6–8 liters per minute. The breathing pattern is regular and effortless, with minimal use of accessory muscles and no significant sensation of breathlessness.

Variations and clinical relevance: Respiratory rates are higher in infants and young children. Eupneic breathing can persist during sleep, though it may be interrupted by normal arousals. Departures from eupnea include tachypnea (increased rate), bradypnea (decreased rate), dyspnea (breathing discomfort or difficulty), and apnea (cessation of breathing), which can indicate underlying pathology or abnormal physiology.

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