One component
is the upper airways, or dead space (trachea and bronchi)
where no gas exchange occurs of volume VD. The other component
is the alveolar compartment of volume VA. The respiratory system
during diving is considered to be a closed system in which air is
free to pass between VA and VD. Consequently, the pressure inside
the respiratory system (Pint) is equal in both VA and VD. Pint is calculated
after a change in the total volume of the respiratory system
(VA + VD) using Boyle’s law.