The effects of ipratropium bromide on histamine-induced bronchoconstriction in subjects with cervical spinal cord injury

Previously, we reported that a majority of subjects with chronic cervical spinal cord injury (SCI) demonstrated airway hyperreactivity in response to inhaled methacholine. To further investigate mechanisms of airway hyperreactivity, 15 male subjects with cervical SCI were challenged with aerosolized histamine, and on a separate day responders were rechallenged 30 min after the inhalation of 72 μg of ipratropium bromide. Twelve of 15 subjects demonstrated airway hyperresponsiveness to histamine (geometric mean PC₂₀ of 1.27 mg/ml), which was not blocked by pretreatment with ipratropium bromide (geometric mean PC₂₀ 1.50 mg/ml). Baseline forced vital capacity and forced expiratory volume in 1 sec were not significantly different between responders and nonresponders (2.8 ± 0.6 vs. 3.0 ± 0.4 L and 2.3 ± 0.6 vs. 2.4 ± 0.2 L, respectively). Findings that subjects with cervical SCI are hyperresponsive to methacholine and histamine, chemical agents with direct action through distinct receptor systems, suggest that bronchial hyperreactivity in these subjects represents a nonspecific process similar to that observed in patients with asthma.