Cardiovascular responses to static exercise in patients with Brown-Séquard syndrome

The purpose of this study was to determine the contributions of central command and the exercise pressor reflex in regulating the cardiovascular response to static exercise in patients with Brown-Séquard syndrome. In this rare condition, a hemisection of the spinal cord typically leaves one side of the body with diminished sensation and normal motor function and the other side with diminished motor function and normal sensation. Four, otherwise healthy, patients with Brown-Séquard syndrome and varying degrees of motor and sensory dysfunction were studied during four isometric knee extension protocols involving both voluntary contraction and electrically stimulated contractions of each leg. Heart rate, blood pressure, force production and ratings of perceived exertion were measured during all conditions. Measurements were also made during post-contraction thigh cuff occlusion and during a cold pressor test. With the exception of electrical stimulation of the leg with a sensory deficit, protocols yielded increases in heart rate and blood pressure. Cuff occlusion sustained blood pressure above resting levels only when the leg had intact sensation. While voluntary contraction (or attempted contraction) of the leg with a motor deficit produced the lowest force, it produced the highest ratings of perceived exertion coupled with the greatest elevations in heart rate and blood pressure. These data show that the magnitude of the heart rate and blood pressure responses in these patients was greatly affected by an increased central command; however, there were marked cardiovascular responses due to activation of the exercise pressor reflex in the absence of central command.