26.12 : 肺通气:呼气

Exhalation — the process of expelling air — during quiet breathing in healthy individuals relies on the elasticity of the lungs rather than muscle contraction.

The recoil of elastic fibers stretched during inhalation primarily causes the recoil of the lungs.

Additionally, the internal pull of surface tension created by the intrapleural fluid layer between the visceral and parietal pleurae contributes to this lung recoil.

As the muscles involved in inhalation stop their activity, the diaphragm and external intercostals relax, causing the diaphragm to ascend and the ribs to descend.

These movements reduce the dimensions of the thoracic cavity, thereby reducing lung volume.

During exhalation, intrapulmonary pressure increases to 1 mm Hg above atmospheric pressure. And when intrapulmonary pressure is greater than atmospheric pressure, gas flows out of the lungs.

In contrast to this quiet exhalation, forceful exhalation includes the contraction of the abdominal and intercostal muscles. It forces the diaphragm to ascend from its normal position to expel the air with force.