Previously it was observed that individuals with tetraplegia have reduced baseline airway
caliber and exhibit non-specific airway hyperresponsiveness (AHR). In persons with
tetraplegia we have suggested that this is due to overriding cholinergic airway tone. In
asthma, the mechanisms underlying bronchoconstriction and AHR are more closely tied to airway
inflammation. Whether AHR in tetraplegia is also related to chronic airway inflammation is
unknown.
Recently, a non-invasive technique for assessing airway inflammation has been established in
asthma that involves measurement of nitric oxide (NO) concentrations (FeNO) in expired air.
FeNO is elevated in asthma likely due to excess NO production by inflammatory cells within
the airway Measurement of FeNO in persons with tetraplegia would help in assessing the role
of airway inflammation in this population. This may have therapeutic significance in such
individuals. NO in the lung is felt to be the principal inhibitory neurotransmitter of the
non-adrenergic, non-cholinergic (NANC) system. It is thought that inhalation of NO has no
effect on airway tone in healthy individuals but reduces methacholine responsiveness while
having weak direct bronchodilatory effect in asthmatics.
The primary purpose of this study is to determine the levels of exhaled NO (FeNO) in
individuals with chronic cervical spinal cord injury (SCI), and to compare them with those
obtained in age and sex matched able-bodied individuals and subjects with stable mild to
moderate asthma. If the FeNO levels are high and comparable to those found in asthmatic
subjects, this will imply the role of chronic inflammation in reduced baseline airway caliber
and non-specific airway hyper-responsiveness (AHR) exhibited by individuals with chronic
cervical SCI. If the FeNO levels are comparable with those found in able-bodied controls,
this will support our previous statement that unopposed cholinergic innervation is
responsible for low baseline airway caliber and AHR in individuals with chronic tetraplegia.
Further scientific conclusions about NO and its role in control of airway tone, pulmonary
resistances and blood pressure will be drawn upon intravenous and inhaled administration of
L-NAME. This compound has been shown promising results for the treatment and prevention of
orthostatic hypotension in individuals with tetraplegia. Knowing its effects on airways and
potential of easier mode of delivery (inhalation vs. intravenous) is of utmost importance.