EFFECT OF PERTURBATIONS AND A MEAL ON SUPERIOR MESENTERIC-ARTERY FLOWIN PATIENTS WITH ORTHOSTATIC HYPOTENSION

Our aims were to evaluate to role of superior mesenteric blood flow in the pathophysiology of orthostatic hypotension in patients with gener alized autonomic failure. Methods: Twelve patients with symptomatic ne urogenic orthostatic hypotension and 12 healthy controls underwent sup erior mesenteric artery flow measurements using Doppler ultrasonograph y during head-up tilt and tilt plus meal ingestion. Autonomic failure was assessed using standard tests of the function of the sympathetic a drenergic, cardiovagal and postganglionic sympathetic sudomotor functi on. Results: Superior mesenteric flow volume and time-averaged velocit y were similar in patients and controls at supine rest; however, respo nses to cold presser test and upright tilt were attenuated (p < 0.05) in patients compared to controls. Head-up tilt after the meal evoked a profound fall of blood pressure and mesenteric blood flow in the pati ents; the reduction of mesenteric blood flow correlated (r = 0.89) wit h the fall of blood pressure in these patients, providing another mani festation of failed baroreflexes. We make the novel finding that the s everity of postprandial orthostatic hypotension regressed negatively w ith the postprandial increase in mesenteric flow in patients with orth ostatic hypotension. Conclusion: Mesenteric flow is under baroreflex c ontrol, which when defective, results in, or worsens orthostatic hypot ension. Its large size and baroreflexivity renders it quantitatively i mportant in the maintenance of postural normotension. The effects of o rthostatic stress can be significantly attenuated by reducing the spla nchnic-mesenteric volume increase in response to food. Evaluation of m esenteric flow in response to eating and head-up tilt provide importan t information on intra-abdominal sympathetic adrenergic function, and the ability of the patient to cope with orthostatic stress. (C) 1997 E lsevier Science B.V.