Respiratory Event-Related Potentials in Patients With Spinal Cord Injury

Dyspnea is "a subjective experience of breathing discomfort that consists of qualitatively
distinct sensations that vary in intensity." Dyspnea, or shortness of breath, is a common
problem affecting up to half of hospitalized patients; and "shortness of breath" and "labored
or difficult breathing" accounts for 3 to 4 million emergency department visits annually.
Dyspnea can represent a sensation, a symptom, or an illness. Each set of experiences involves
distinct sensory, perceptual, and cognitive processes, including: the detection of signals;
the perception of threat or remarkable challenge; and, the construction, or mental
representation, of illness. As a sensory experience dyspnea can be compared to the sensation
of pain. Although labored breathing is not painful in the usual sense of the word dyspnea,
like pain, is a concept varying along multiple dimensions. Like pain, dyspnea can signal the
need for medical attention; but unlike pain dyspnea is a localized sensation originating in
the cardiopulmonary system rather than a generalized danger signal.

Research demonstrates that sensory information from the respiratory system activates regions
of the cerebral cortex to produce the perception of dyspnea but far less is known about the
neurophysiology of dyspnea than about vision, hearing, or even pain. Dyspnea likely arises
from multiple nervous system sources. Investigations of the mechanisms underlying respiratory
sensations have included studies of airway anesthesia, chest wall strapping, exercise,
heart-lung transplantation, hyperventilation, and opioid use. Study of the perception of
breathing sensations in individuals with a spinal cord injury presents additional
opportunity. The goal of the proposed project is to examine the effects of increasingly
severe levels of spinal cord injury on the perception of breathing sensations in participants
who are able to breathe without the use of a ventilator.

Afferent pathways that transmit somatosensory signals to the central nervous system (i.e.,
brain and spinal cord) are well described and event-related potentials have been used to
measure respiratory somatosensation with high temporal resolution. Event-related potentials
(ERPs) are time-locked cortical signals that are measured non-invasively from the surface of
the scalp in response to brief (< 200 msec), presentations of respiratory stimuli during
normal breathing. Davenport et al. first identified sensory-perceptual ERPs to inspiratory
stimuli (those occurring about 50-150 msec after stimulus delivery) and Harver et al. first
examined perceptual-cognitive ERPs to inspiratory stimuli (those occurring about 150-400 msec
post-stimulus). Study of respiratory-related ERPs in patients with spinal cord injuries
presents a rare opportunity to examine the neurophysiological mechanisms underlying the
perception of breathing because the extent of somatosensory information that reaches cerebral
cortex varies with level of lesion.

Inclusion Criteria:

- Participants with spinal cord injury (n = 20) will be age 30-60 years with motor
complete spinal cord injuries, otherwise known as American Spinal Injury Association
(ASIA) classification A or B, between the levels of C3 and T12. Subjects will be
divided equally into four different injury level categories. The four categories are
high tetraplegia (C3 - C5), low tetraplegia (C6-C8), high paraplegia (T1-T6), and low
paraplegia (T7-T12). Twenty healthy age-matched adults will also participate.

Exclusion Criteria:

- History or presence of lung disease (asthma, chronic bronchitis, etc)

- Current smoker (more than one cigarette per day the past year)

- History of traumatic brain injury, epilepsy, or seizure; using psychotropic medication
of any type

- And, if patient, more than six months since spinal cord injury and clinically stable.