Noninvasive quantification of superior mesenteric artery blood flow during sympathoneural activation in normal subjects

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Abstract
The role of the splanchnic circulation in normal subjects during sympathoneural activation induced by stimuli which either raise (mental arithmetic, cold pressor test, isometric exercise) or maintain (head-up tilt) blood pressure has been studied by measuring superior mesenteric artery blood flow using a noninvasive Doppler ultrasound method in 18 normal subjects. Cardiac, systemic and regional haemodynamic changes were simultaneously studied. Blood pressure rose with the pressor tests and was maintained with head-up tilt. There was a significant fall in superior mesenteric artery blood flow with a rise in vascular resistance during each stimulus incidating active constriction. In six subjects, after 2 months measurements were repeated in an identical study. Superior mesenteric artery blood flow measurements in this study were closely correlated with the initial results. These changes, in a large vascular bed, are likely to be of importance in the overall haemodynamic response during sympathoneural stimuli which either raise or maintain blood pressure.