Assessment of upper airway obstruction by pulmonary function testing.

Twenty-five cases of upper airway obstruction (UAO) of different diseases and ten normal healthy controls were studied by deriving parameters from raw data on Gould System-21 Pulmonary Work station. All the obstructive lesions were confirmed under direct visualisation by fibreoptic bronchoscopy or indirect laryngoscopy. It was observed that FEF 50%/FIF 50% ratio above 1 was the best diagnostic indicator for fixed and variable extrathoracic UAO (p < 0.02). FEV1/PEFR was altered significantly (p < 0.001) and value above 10 ml/Litre/min was the second best parameter to recognise UAO. FEV1 0.5 < or = 1.5 (p < 0.001) and FIF 50% < 100 Lit/min were also suggestive of UAO. Flow volume loop remained the most sensitive method to detect UAO but only 15 patients could construct it. These altered parameters returned to normal after the surgical removal of obstruction which was possible in three cases.