Respiratory Event-Related Potentials in Patients With Spinal Cord Injury: An Evaluation of Somatosensory Afferents

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.