Rate of gastric emptying is a determinant of postprandial hypotension in non-insulin-dependent diabetes mellitus.

1. Postprandial hypotension is now recognized as an important clinical problem, particularly in the elderly and in patients with autonomic dysfunction. The mechanisms responsible are poorly understood; however, impaired regulation of splanchnic blood flow and the release of gastrointestinal hormones appear to be important. The effect of gastric emptying on the magnitude of the postprandial fall in blood pressure has not been evaluated. 2. The aim of this study was to determine whether there is a relationship between changes in blood pressure and the rate of gastric emptying after ingestion of 75 g of glucose in patients with non-insulin-dependent diabetes mellitus (NIDDM) and both young and older normal subjects. Sixteen patients with recently diagnosed NIDDM, median age 57 (39-79) years, 10 'young' subjects with a median age of 23 (19-26) years and nine 'older' subjects, median age 48 (40-68) years, were measured simultaneously for gastric emptying of 75 g of glucose in 350 ml of water blood pressure and blood glucose concentrations, commencing at approximately 10.00 hours after an overnight fast. Measurements of blood pressure were made in the sitting position immediately before glucose ingestion and at 15 min intervals up to 180 min. 3. Gastric emptying of glucose was not significantly different between the three groups [50% emptying time (T50): 95 +/- 7.3 min in patients with NIDDM compared with 120 +/- 13.2 min in the 'young' group and 97 +/- 8.1 min in the 'older' group]. There was a significant fall in mean blood pressure after the glucose load in the patients with NIDDM (P < 0.0001) and the 'older' normal subjects (P < 0.05), but not the 'young' normal subjects. Postprandial hypotension (fall in systolic blood pressure > or = 20 mmHg) was evident in seven (44%) patients with NIDDM and three (33%) 'older' normal subjects. The area under the change in mean blood pressure curve was related significantly to the gastric emptying T50 (r = 0.67, P < 0.005) in the patients with NIDDM, but not in either control group. 4. In conclusion, in patients with recently diagnosed NIDDM the fall in blood pressure after an oral glucose load is (i) greater than in both young and older normal subjects and (ii) related to the rate of gastric emptying.