The one-way endobronchial valve is typically implanted such that on exhalation air is able to flow through the valve and out of the lung compartment that is fed by that airway, but on inhalation, the valve closes and blocks air from entering that lung compartment. Thus, an implanted endobronchial valve typically helps a lung compartment to empty itself of air. This has been shown to be beneficial in the treatment of emphysema, where lungs lose their elasticity and thus cannot contract sufficiently to exhale air, leading to air trapping and hyperinflation.
The one-way endobronchial valve is usually positioned so that airflow can escape from a lung compartment connected to it during expiration, but it closes during inspiration, preventing air from entering that compartment. This function facilitates the expulsion of air from the lung compartment, which has been demonstrated to be advantageous in treating emphysema.