During respiratory inspiration, the negative intrathoracic pressure causes increased blood return into the right side of the heart.

Thus, S2 is split to the same degree during inspiration as expiration, and is said to be "fixed."

However there has been argument that caval opening actually constricts during inspiration.

Thus gas is pushed into the lung during inspiration, and then pulled out during expiration.

Thus will appear to increase when the subject is not at rest, particularly during inspiration.

Flow rates exceeding inspiratory demand may also provide positive pressure during inspiration.

Crackles (rales) may be heard over the affected area during inspiration.

These are the result of alveoli opening due to increased air pressure during inspiration.

The lung expands into the costomediastinal recess even during quiet inspiration.

Abdominal breathing is noted when the abdomen protrudes during inspiration.