Inspiratory flow volume loops and the diagnosis of upper airway obstruction

As part of the evaluation process of patients with pulmonary symptoms, the flow volume loop (FVL) may be important in identifying the presence of functional or anatomic airway abnormalities. Typical patterns in both the expiratory and inspiratory limbs help identify either restrictive or obstructive lung diseases. The inspiratory limb of the FVL has been advocated as a predictor for the presence of extrathoracic upper airway obstruction (UAO) in patients with associated symptoms. The recently published guidelines on pulmonary function testing interpretation emphasize FVL review for suspected UAO. It was first clinically described in the early 1970s by Miller and Hyatt in patients with known tracheal stenosis, airway tumors, and vocal cord paralysis. It can help to identify and manage some chronic anatomic causes of UAO such as goiter and vocal cord paralysis. Its usefulness as a diagnostic test is increasing in more functional upper airway diseases, such as vocal cord dysfunction or neuromuscular disease. This review carefully examines the available literature on the inspiratory FVL to identify those clinical entities in which it has proven to be a useful diagnostic test.