That expansion drops your lungs internal air pressure, making air rush in.

这种扩张会降低肺部的内部气压，使空气涌入。

The diaphragm contracts and descends with each inhalation (inspiration). The downward movement of the diaphragm enlarges the area in the thoracic cavity and reduces the internal air pressure, so that air flows into the lungs to equalize the pressure.

每次吸气（吸入）隔膜收缩并下降。隔膜向下运动扩大胸腔内的面积并降低内部气压，使空气流入肺部以平衡压力。