Dynamic hyperinflation during controlled ventilation in obstructive lung disease

During resting ventilation of normal lungs or controlled ventilation of lungs with decreased lung compliance (eg, ARDS), passive exhalation leads to a return to normal FRC at the end of each breath. However, in patients with airway obstruction, such as asthma or COPD, exhalation may not be complete at the time the next breath is initiated, leading to increasing amounts of trapped air at end-exhalation, a process known as dynamic hyperinflation. In this figure, the tidal volume curve in blue reflects ventilation of normal lungs and shows a return to the normal FRC at the end of each exhalation. The tidal volume curve in green shows the progressive increase in end-expiratory volume in a patient with asthma or COPD when successive breaths are initiated before complete exhalation. Dynamic hyperinflation can occur in patients with airway obstruction during mechanical ventilation or with exercise.

Dynamic hyperinflation is associated with increased intrathoracic pressure and potentially decreased venous return to the heart. Dynamic hyperventilation is treated by decreasing minute ventilation (ie, reducing tidal volume and/or respiratory rate) and sometimes by shortening inspiratory time to enable adequate time for exhalation.