2315 Intrapulmonary and Intrapleural Pressure

Alveolar pressure (P_alv) is the pressure of

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

inside the

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

. When the

glottis The glottis (: glottises or glottides) is the opening between the vocal folds (the rima glottidis). The glottis is crucial in producing sound from the vocal folds. Etymology From Ancient Greek ''γλωττίς'' (glōttís), derived from ''γ ...

is opened and no air is flowing into or out of the lungs, alveolar pressure is equal to the atmospheric pressure, that is, zero cmH₂O.Guyton and Hall Textbook of Medical Physiology, 12th edition. 23 May 2016

Significance

During

inhalation Inhalation (or inspiration) happens when air or other gases enter the lungs. Inhalation of air Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...

, the increased volume of

as a result of

expansion decreases the intra-alveolar pressure to a value below atmospheric pressure about -1 cmH₂O. This slight negative pressure is enough to move 500 ml of air into the lungs in the 2 seconds required for inspiration. At the end of inspiration, the alveolar pressure returns to atmospheric pressure (zero cmH₂O). During

exhalation Exhalation (or expiration) is the flow of the breathing, breath out of an organism. In animals, it is the movement of air from the lungs out of the airways, to the external environment during breathing. This happens due to elastic properties of ...

, the opposite change occurs. The lung alveoli collapse before air is expelled from them. The alveolar pressure rises to about +1 cmH₂O. This forces the 500 ml of inspired air out of the lung during the 2–3 seconds of expiration. By the end of expiration, the pressure drops gradually and becomes atmospheric again.

References

{{reflist Respiratory therapy Pulmonology Mechanical ventilation