Exhaled Breath Condensate Biomarkers of Inflammation in Individuals With Chronic Cervical Spinal Cord Injury

The predominant mechanism for pulmonary dysfunction in individuals with chronic tetraplegia is respiratory muscle paralysis. This leads to inadequate ventilation and inability to clear secretions placing these patients at a greater risk for the development of respiratory complications. Furthermore, individuals with chronic tetraplegia exhibit baseline increases in airway tone (bronchoconstriction), restoration of normal airway caliber following bronchodilator administration, and non-specific airway hyperresponsiveness (AHR) following inhalation of methacholine, histamine, an aerosolized distilled water. These findings in persons with spinal cord injury (SCI) represent pulmonary features commonly seen in individuals with asthma. Alternatively, airway inflammation may play a role in the obstructive physiology observed in individuals with tetraplegia. In this population, identification of cellular inflammation would confirm the presence of underlying inflammation with a sputum induction. However, this method is hard to perform due to an impaired cough. The emerging field of exhaled breath condensate (EBC) biomarkers of inflammation offers a non-invasive technique to define the presence of, and potentially address the contributing factors of airway inflammation in the respiratory tract of individuals with tetraplegia. It is thought that EBC composition reflects biochemical changes of airway lining fluid. EBC contains a large number of mediators, including adenosine, ammonia, hydrogen peroxide (H2O2), isoprostanes, leukotrienes, prostanoids, peptides and cytokines. Looking at exhaled breath profiles of various biomarkers may be used to differentiate their different pathophysiological mechanism of inflammation. In addition, measurements of some chemokines (TNF-ά, interleukin (IL)-6) and inflammatory biomarkers (LTB4) in EBC and blood simultaneously may help differentiate the degree of local vs. systemic inflammation. Understanding the underlying mechanisms involved in pulmonary dysfunction observed in persons with chronic cervical SCI may identify treatment options, such as use of inhaled steroids. This approach would be expected to ultimately improve quality of life in affected individuals, decreasing the rate of re-hospitalizations due to respiratory complications and the socioeconomic burden placed on these with SCI and the health care system.