Stridor: differentiation from asthma or upper airway noise.

Stridor, a musical, continuous sound often attributed to upper airway narrowing, may be encountered in the recently extubated patient. Recently extubated patients and patients with documented upper airway obstruction were studied. Sounds were recorded from the neck and chest. The sound signal of patients with stridor was compared to that made by asthmatics and extubated patients with no airway obstruction. The frequency spectrum of segments of the sound signal was determined using the fast fourier transform technique. The sound signal associated with stridor had a similar frequency to that found with asthma. However, the signal was more intense over the neck than over the chest, whereas in asthmatics the reverse was true. The musical sounds in patients with stridor occurred during inspiration, whereas in those patients with asthma, they were predominantly expiratory. The major difference between stridor and asthma was the timing of the sound and the prominence of the sound over the neck.