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Increased frequency dependence of specific airway resistance in patients with laryngeal hemiplegia

¹ Institute of Respiratory Diseases, ² Ear, Nose and Throat Institute and ³ Epidemiology Unit, University of Milan, Ospedale Maggiore of Milan, IRCCS, Italy

CORRESPONDENCE: V. Fasano, Institute of Respiratory Diseases, Pad. Litta Ospedale Maggiore of Milan IRCCS Via F. Sforza, 35 20122, Milano, Italy. Fax: 39 0255190332

Keywords: Body plethysmography, forced inspiratory flow at 50% of the vital capacity, inspiratory flow, laryngeal hemiplegia, specific airway resistance

Received: July 7, 2000
Accepted July 18, 2001

The aim of this study was to investigate whether patients with laryngeal hemiplegia (LH) show a frequency-dependent increase in specific airway resistance (sR_aw), measured by body plethysmography.

In addition to the flow-volume loop, usually considered in the functional evaluation of upper airway obstructions, variations in sR_aw at respiratory frequencies of 30±5 (=0.5 Hz), 60±5 (=1 Hz) and 90±5 breaths·min^–1 (=1.5 Hz) in 21 never-smoking patients (LH group, mean age±sd 55±12.09 yrs; 17 females) whose unilateral vocal-cord paralysis was documented by laryngoscopy and who had no signs or symptoms of other respiratory diseases studied. They were compared to 21 healthy control subjects (C group: 50.1±15.44 yrs; 10 females).

The sR_aw values at 30±5 breaths·min^–1 were similar in the two groups (5.54±1.88 versus 5.68±1.06 cmH₂O·s^–1; p=ns), but at increasing frequencies (30±5, 60±5 and 90±5 breaths·min^–1), they progressively and significantly increased in the LH patients (from 5.54±1.88 to 6.63±1.96 and 8.05±2.6 cmH₂O·s^–1; p<0.0005), and not significantly in controls (5.68±1.06, 5.85±0.95 and 5.9±1.12 cmH₂O·s; p=ns). Linear discriminant analysis using sR_aw (sR_aw at 1.5 Hz-sR_aw at 0.5 Hz) and forced inspiratory flow at 50% of the vital capacity made it possible to correctly classify all of the controls and 19 of the 21 patients.

In conclusion, the multiple, rapid and noninvasive plethysmographical testing of frequency-dependent increase in specific airway resistance with the flow-volume loop, allows the sufficiently satisfactory discrimination of laryngeal hemiplegia patients from controls.