Dynamic hyperinflation


Dynamic hyperinflation is a phenomenon that occurs when a new breath begins before the lung has reached the static equilibrium volume.

Asthma

Dynamic hyperinflation can occur in patients with asthma who are breathing spontaneously. It is a physiologic response to airflow obstruction and exists, to an extent, because increasing lung volume tends to increase airway caliber and can reduce the resistive work of breathing. However, in patients with severe asthma it becomes maladaptive, occurring at the expense of increased mechanical load and elastic work of breathing. Dynamic hyperinflation can cause alveolar overdistention resulting in hypoxemia, hypotension, or alveolar rupture. Dynamic hyperinflation increases the magnitude of the drop in airway pressure that the patient must generate to trigger a breath, thereby increasing the patient's workload.

Status asthmaticus

Patients with acute severe asthma exacerbation are at risk for progressive air trapping and alveolar hyperinflation, which may lead to alveolar rupture and hemodynamic compromise. Airflow obstruction during expiration slows lung emptying and inspiration may be initiated before exhalation is complete. The phenomenon that occurs when a new breath begins before the lung has reached the static equilibrium volume is called dynamic hyperinflation.

Interventions

Interventions to correct air-trapping include decreasing the respiratory rate, increasing inspiratory flow rates and lowering the tidal volume.

Adults

In adults, it has been demonstrated that limiting minute ventilation is the key to avoiding dynamic hyperinflation; keeping the minute ventilation under 115/mL/kg is recommended