Breathing, defined as the exchange of gases between the respiratory system and the environment, is an essential process for life. The human respiratory system can be divided into three parts: (i) nose, mouth, and nasopharynx, (ii) trachea, and (iii) lungs. The human lung can be further subdivided into conducting airways which are non-alveolated and comprise the upper part of lung, and the acini which consist of flexible, alveolated airways and are responsible for gas exchange [1]. The alveoli collectively provide a large surface area (∼70 m2) for efficient gas exchange [1]; oxygen diffuses into the blood through the alveolar epithelium, whereas carbon dioxide diffuses in the opposite direction from the blood to the lung.

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