Regulation of total and regional spinal cord blood flow.

Studies of the regulation of total spinal cord blood flow have been limited by methodology. Total flow has been difficult to measure and flow to the gray and white matter within the cord has not been previously assessed. We have used labeled microspheres to measure blood flow in the spinal cord. Our purpose was to examine the effects of several physiological stimuli on the regulation of blood flow to different regions of the spinal cord (cervical, thoracic, and lumbosacral) and to different tissue in the cord (gray and white matter). The four types of stimuli examined were: chemical stimulation (alterations in systemic blood gases); autoregulation (increases in systemic pressure); neurogenic stimulation (activation of chemoand baroreceptor reflexes); and metabolic stimulation (activation of spinal cord neurons). Studies were performed in dogs, sheep, and lambs; cerebral flow and spinal cord flow were measured simultaneously. Mean blood flow to the cervical and lumbosacral cord segments was 40% higher than flow to the thoracic cord. Under control conditions gray and white matter flows to the lumbosacral cord of sheep were 110 ± 15 (mean ± SE) and 25 ± 6 ml/min per 100 g, respectively. Chemical stimulation markedly altered spinal cord blood flow (hypoxia and hypercapnia increased flow; hypocapnia decreased flow), and distribution of flow to gray and white matter was unchanged. Autoregulation maintained total and regional spinal cord flow constant during increases in systemic pressure. Neurogenic stimulation did not alter the tone of spinal cord blood vessels. Metabolic stimulation selectively increased blood flow to gray matter of the stimulated region. Regulation of total and regional spinal cord blood flow generally parallels that of the brain; chemical, autoregulatory, and metabolic factors are important determinants in the control of spinal cord blood flow.