Maximal mid-inspiratory to maximal mid-expiratory flow rate ratio in upper airway obstruction.

The maximal mid-inspiratory to maximal mid-expiratory flow rate ratio (MMIF/MMEF) was measured in 16 patients with upper airway obstruction, in eight with pleural disease, in 25 with chest wall abnormalities, in 64 with various lung diseases and in 28 normal subjects. MMIF/MMEF ratio values of less than 1.0 were recorded in eight out of 16 patients with upper airway obstruction, in nine out of 25 patients with chest wall abnormalities and in one normal subject. Our findings show that a MMIF/MMEF ratio less than 1.0 although suggestive, is not diagnostic of upper airway obstruction. However, reduced MMIF/MMEF ratio in the presence of airflow obstruction is specific in localizing obstruction to the upper airway.