Spirometric and plethysmographic assessment of upper airway obstruction in laryngeal hemiplegia

Laryngeal hemiplegia (LH) is the most common disorder of laryngeal motility. It is deemed not to cause obstruction of the upper airway; in fact, the main symptoms are dysphonia and breathiness, and respiratory impairment is not commonly reported. The aim of this study was to objectively assess upper airway patency in 41 patients affected by LH (mean age, 54.4 ± 15.2 years; 27 female) and 30 controls (mean age, 50.0 ± 16.1 years; 19 female) by means of flow-volume loop spirometry and body plethysmography to measure specific airway resistance (sRaw) at increasing respiratory frequencies. The causes of LH were cervical surgery (28), tumor infiltration (5), and unexplained (8). None of the patients or controls was affected by lower airway disease. Spirometry showed that the patients had inspiratory flows (PIF, FIF50) significantly lower than those of the controls (p <.0001), whereas the expiratory flows (FEV1, FEF50) were normal, with the exception of peak expiratory flow (PEF), which was reduced, especially in female patients. The mean FEF50/FIF50 ratio (about unity in the normal subjects) was > 1, as is typical of variable extrathoracic obstruction. Plethysmography showed that the values of sRaw of the LH group were not statistically different from those of the controls at 30 ± 5 breaths per minute, but they progressively and significantly increased at 60 ± 5 (p <.01) and 90 ± 5 breaths per minute (p <.002), whereas no significant sRaw change was observed in the controls. These results show that LH causes obstruction of the upper airway that can be assessed and quantified by means of spirometry and body plethysmography. A dynamic narrowing due to inspiratory medialization of the paralytic vocal fold and flow turbulence during hyperventilation seem to be the causes of patency impairment. The flow-volume loop is an excellent, inexpensive, and easily available means of functionally evaluating upper airway obstruction, but some patients have difficulty in performing an inspiratory test that requires maximal effort, and the flow reduction during forced ventilation may be partially due to the effort dependency of the tests themselves. Plethysmographic assessment of airway resistance may be a valid alternative or complement, as it reveals an increase in sRaw at increasing respiratory frequencies.