Why must lungs always be partially inflated?

Lungs must always be partially inflated due to the presence of residual volume, which is the air remaining in the lungs after exhalation. This residual air prevents the alveoli from collapsing and ensures that gas exchange can continue even between breaths. Additionally, maintaining some level of inflation helps keep the lung tissues flexible and reduces the work required for subsequent inhalations. This partial inflation is crucial for efficient respiratory function and overall pulmonary health.