The Pulmonary flow-volume loop is a plot of inspiratory & expiratory flow (on the Y-axis) and volume (on the X-axis) during maximally forced inspiratory and expiratory movements. Changes in the contour of the loop can help in the diagnosis and localization of airway obstructive diseases.
The normal Flow volume loop looks like the pic above.
There are 3 types of obstructions that can happen in our respiratory tract.
A. Dynamic Extrathoracic
Tip to remember: Extrathoracic=Exhalation loop has no problem.
Seen in Vocal cords dysfunction, Epiglottitis.
B. Fixed Extrathoracic
Both inhalation and Exhalation loops are affected.
Seen in Tracheal Stenosis.
C. Dynamic Intrathoracic
Tip to remember: Intrathoracic=Inhalation loop has no problem.
Seen in Tracheomalacia.