Final answer:
The volume change per unit transpulmonary pressure change is an indicator of lung distensibility. Boyle's law relates the pressure and volume of a gas, which explains the changes in lung pressure during inhalation and exhalation.
Step-by-step explanation:
The volume change per unit transpulmonary pressure change is an indicator of how distensible the lung is. This is related to the ability of the diaphragm to contract and relax to change the volume of the lung, which is known as inspiration. The lungs control the volume of air by altering the air pressure of the thoracic cavity, as described by Boyle's law, which states that the pressure of a gas is directly proportional to its volume.