Analyzing flow volume loops provides a quick way to detect lung disease. The appearance of the loop can reveal the presence of obstructive and/or restrictive lung disease.
The location of the airway obstruction can also be identified from the shape of the flow volume loop.
In a spontaneously breathing patient, the flow volume loop is measured using a forced vital capacity maneuver (FVC). The patient is instructed to take a maximum deep breath (to total lung capacity). They then forcefully exhale all of the air out completely (to residual volume). When they can no longer exhale, they take a forceful breath back in to total lung capacity.
Flow volume loops can also reveal the presence of airway secretions during mechanical ventilation that auscultation alone may miss.
As air passes by secretions in the airway, tiny flow and pressure changes occur. These tiny changes produce a saw tooth pattern during inhalation and exhalation. (the FVC maneuver is not required to detect secretions during mechanical ventilation).