26.10 : 胸腔内的压力关系

Healthy respiration in humans requires proper air pressure levels in different respiratory organs.

These pressures are expressed relative to the atmospheric pressure, equivalent to 760 mm Hg or one atmospheric pressure.

First, intrapulmonary pressure is the pressure in the alveoli. It fluctuates with each breath but eventually equalizes with the atmospheric pressure.

Second, intrapleural pressure is the pressure in the pleural cavity. It is typically 4 mm Hg lower than the atmospheric pressure.

The negative intrapleural pressure results from opposing forces in the thorax. The surface tension in alveolar fluid and the lungs' natural tendency to recoil try to collapse the lungs completely during exhalation.

But, the elasticity of the chest wall counters this, and a strong adhesive bond between the pleurae keeps the lungs from deflating completely.

The difference between intrapulmonary pressure and intrapleural pressure, also known as transpulmonary pressure, is pivotal in preventing lung collapse by keeping the air sacs open.

As a result, when the difference between the intrapulmonary pressure and the intrapleural pressure is larger, the lungs are more inflated.