24hr Effects of Tiotropium Bromide in Tetraplegia

Overview

Respiratory complications are the leading cause of death during the initial year after acute SCI, and the third leading cause of death thereafter. Complete or partial loss of respiratory muscle innervations in individuals with cervical and high thoracic injuries leads to inadequate ventilation and inability to effectively clear secretions, often prompting supportive ventilation following initial injury. Development of atelactasis, pneumonias and respiratory failure are the most common respiratory complications observed during the acute phase of injury. It is well known that a restrictive ventilatory defect, dependent upon the level and completeness of injury, is apparent in individuals with chronic cervical SCI. Respiratory functional impairment might be further compromised in these individuals, the majority of whom share many aspects of obstructive airway physiology commonly associated with asthma. The asthma-like features that individuals with chronic cervical SCI demonstrate have been hypothesized to be due to overriding cholinergic airway tone carried by intact vagal (parasympathetic) nerve fibers arising from the brainstem, whereas sympathetic innervations is interrupted at the level of the upper thoracic spinal cord. Whether airway narrowing and AHR in chronic cervical SCI is also related to chronic airway inflammation is unknown, although it is conceivable that repeated respiratory infections or, possibly, a neurogenic component, could contribute to chronic airway inflammation. Therefore, the investigators aim to assess how long-acting bronchodilator (tiotropium bromide) affects various indices of lung function, including: pulmonary function tests, levels of inflammation and cough strength across 24 hours after receiving study drug. Results will be analyzed for baseline, 1 hour, 3 hours, 20 hours and 24 hours post drug inhalation for both active medication and non-active placebo.

In addition to a restrictive ventilatory defect stemming for respiratory muscle paralysis, cervical SCI (tetraplegia) is associated with obstructive airway physiology similar to that associated with asthma. The investigators hypothesize that these aspects of obstructive physiology stem from unopposed increases in cholinergic airway tone as a result of autonomic imbalance; where vagal innervation (cholinergic neurotransmission) to the lungs is intact, and the bronchodilating adrenergic influences of sympathetic pathways are interrupted. The investigators demonstrated using spirometric criteria, significant bronchodilator responses in approximately 50% of subjects with tetraplegia following inhalation of short acting beta-2 agonists (albuterol sulfate) and anticholinergic agents (ipratropium bromide). When specific airway conductance (sGaw), a more sensitive indicator of bronchodilation, was assessed via whole body plethysmography, significant bronchodilation and restoration of normal airway caliber was noted in all subjects. Intuitively, one might expect that through bronchodilation susceptible individuals with tetraplegia who already have compromised respiratory muscle strength and weakened cough might benefit from better airway clearance, and via increases in lung volumes improve the length-tension relationship of residual expiratory muscles for initiation of more forceful coughs. Based upon a comparative study of the bronchodilator effects of ipratropium bromide versus albuterol in persons with tetraplegia (in publication), it appears that ipratropium bromide elicited greater bronchodilation, perhaps because of the specificity of action in blocking acetylcholine binding to the muscarinic-3 (M3) airway smooth muscle receptor. The investigators purpose in this preliminary study is to assess whether salutary effects upon pulmonary function, cough strength, and airway inflammation are observed across a twenty-four hour period following inhalation of a single dose of tiotropium bromide 18 mcg inhalational capsule versus placebo utilizing a double-blind crossover design in persons with chronic stable tetraplegia.