Autonomic Function Tests In Diabetics With Enteropathy

While general autonomic reflex tests (62) are useful to assess the function of the autonomic control of the viscera (Table 3), tests that are specific for gut autonomic innervation are:

(A) Pancreatic polypeptide response to hypoglycemia or to modified sham feeding by the "chew and spit" technique: Pancreatic polypeptide concentrations rise after meal ingestion and delivery of nutrients to the duodenum (63). Atropine or vagotomy abolish this response. Normally, pancreatic polypeptide concentrations should increase by at least 25 pg/ml during sham feeding. The modified sham feeding test seems to be a more sensitive means of detecting vagal dysfunction than the postprandial response of plasma pancreatic polypeptide. The coexistence of antral hypomotility with abnormal pancreatic polypeptide responses to sham feeding further supports the presence of vagal dysfunction or impaired gastric emptying of solids in these situations.

(B) R-R interval response to deep breathing: This is a test of cardiovagal reflexes. However, Buyschaert et al. (64) showed that this is a good surrogate for the testing of abdominal vagal function, consistent with the concept that vagal denervation, as with most forms of diabetic neuropathy commences caudally and progresses in a cranial direction.

(C) Mesenteric flow in response to tilt-table tasting (65): Splanchnic blood flow is under baroreflex control, and appropriate regulation is important in the maintenance of postural normotension. Evaluation of mesenteric flow in response to eating and head-up tilt provides important information on intra-abdominal sympathetic adrenergic function, and the ability of the patient to cope with orthostatic stress. Superior mesenteric artery flow in response to perturbations such as tilting and meal ingestion assesses sympathetic adrenergic function in the abdomen. While useful, this technique requires considerable expertise and is not widely available.

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