What happens when the pressure within the pulmonary cavity is higher than the atmospheric pressure?

The breathing rate of a normal healthy man is

Explain the mechanism of expiration.

The contraction of the diaphragm increases the volume of the thoracic cavity in which axis?

Arrange the given steps of expiration in the sequence of events occurring first:
$I.$ Relaxation of the diaphragm and sternum
$II.$ Reduction of the pulmonary volume
$III.$ Expulsion of air from the lungs
$IV.$ Increase in intra-pulmonary pressure
Choose the correct option.

What is the shape of the diaphragm during expiration?