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

The aim of this study was to investigate whether patients with laryngeal hemiplegia (LH) show a frequency-dependent increase in specific airway resistance (sRaw), measured by body plethysmography. In addition to the flow-volume loop, usually considered in the functional evaluation of upper airway obstructions, variations in sRaw 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 vocalcord 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 sRaw 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 ΔsRaw (sRaw at 1.5 Hz-sRaw 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.