What causes the greatest change in thoracic volume during quiet inspiration? What causes the greatest change in thoracic volume during quiet inspiration? Relaxation of the internal intercostal muscles Contraction of the diaphragm Increased intrapleural pressure Air flowing into the lungs

Contraction of diaphragm causes the greatest change in thoracic volume during quiet inspiration.

Explanation:

Quiet respiration is an active process involving:

1) Contraction (Descent) of diaphragm : It results in increase in the vertical diameter causing the greatest change in thoracic volume.

2) Elevation of ribs (External intercostal) : It results in an increase in anterposterior and lateral diameter