Why the study?
Does the level of sympathetic innervation (paraplegia vs tetraplegia vs intact) affect heart rate, blood pressure, and cardiac output control during dynamic exercise?
Does the level of sympathetic innervation (paraplegia vs tetraplegia vs intact) affect heart rate, blood pressure, and cardiac output control during dynamic exercise?
An intact autonomic nervous system is essential for a large rise in cardiac output during exercise, and sympathetic injury affecting the heart leads to blood pressure challenges from muscle vasodilation.
Exercise-induced BP decline in SCI, especially tetraplegia, warrants monitoring; supports sympathetic role in CO but leaves open causal confirmation.
BACKGROUND: We studied the role of the central nervous system, neural feedback from contracting skeletal muscles, and sympathetic activity to the heart in the control of heart rate and blood pressure during 2 levels of dynamic exercise. METHODS AND RESULTS: Spinal cord-injured individuals (SCI) with (paraplegia, n=4) or without (tetraplegia, n=6) sympathetic innervation to the heart performed electrically induced exercise. Responses were compared with those established by able-bodied individuals (control, n=6) performing voluntary exercise at a similar pulmonary oxygen uptake. In all subjects, cardiac output and leg blood flow increased, but in SCI they reached a maximal value. The increase in cardiac output was mainly elicited by an increase in stroke volume in individuals with tetraplegia, whereas in individuals with paraplegia it was by heart rate. The increase in SCI was slow compared with that in controls. During exercise, blood pressure was stable in controls, whereas it decreased over time in SCI and especially in individuals with tetraplegia. CONCLUSIONS: The autonomic nervous system provides for acceleration of the heart at the onset of exercise, but a slow increase in heart rate is established even without central command, neural feedback from working muscles, or autonomic influence on the heart. Yet an intact autonomic nervous system is a prerequisite for a large rise in cardiac output and in turn leg blood flow during exercise. Thus, when the sympathetic nervous system is injured at a level where it influences the heart, vasodilatation in working muscles challenges blood pressure.
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Dela et al. (2003) studied this question.
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