Airway hyperresponsiveness to ultrasonically nebulized distilled water in subjects with tetraplegia

The majority of otherwise healthy subjects with chronic cervical spinal cor d injury (SCI) demonstrate airway hyperresponsiveness to aerosolized methac holine or histamine. The present study was performed to determine whether u ltrasonically nebulized distilled water (UNDW) induces airway hyperresponsi veness and to further elucidate potential mechanisms in this population. Fi fteen subjects with SCI, nine with tetraplegia (C4-7) and six with parapleg ia (T-9-L-1), were initially exposed to UNDW for 30 s; spirometry was perfo rmed immediately and again 2 min after exposure. The challenge continued by progressively increasing exposure time until the forced expiratory volume in 1 s decreased 20% or more from baseline (PD20) or the maximal exposure t ime was reached. Five subjects responding to UNDW returned for a second cha llenge 30 min after inhalation of aerosolized ipratropium bromide (2.5 mi o f a 0.6% solution). Eight of nine subjects with tetraplegia had significant bronchoconstrictor responses to UNDW (geometric mean PD20 = 7.76 +/- 7.67 mi), whereas none with paraplegia demonstrated a response (geometric mean P D20 = 24 mi). Five of the subjects with tetraplegia who initially responded to distilled water (geometric mean PD20 = 5.99 +/- 4.47 mi) were not respo nsive after pretreatment with ipratropium bromide (geometric mean PD20 = 24 mi). Findings that subjects with tetraplegia are hyperreactive to UNDW, a physicochemical agent, combined with previous observations of hyperreactivi ty to methacholine and histamine, suggest that overall airway hyperresponsi veness in these individuals is a nonspecific phenomenon similar to that obs erved in patients with asthma. The ability of ipratropium bromide to comple tely block UNDW-induced bronchoconstriction suggests that, in part, airway hyperresponsiveness in subjects with tetraplegia represents unopposed paras ympathetic activity.