Comparative effects of oral and intraduodenal glucose on blood pressure, heart rate, and splanchnic blood flow in healthy older subjects.

Postprandial hypotension occurs frequently, particularly in the elderly. The magnitude of the fall in blood pressure (BP) and rise in heart rate (HR) in response to enteral glucose are greater when gastric emptying (GE) or small intestinal infusion are more rapid. Meal ingestion is associated with an increase in splanchnic blood flow. In contrast, gastric distension may attenuate the postprandial fall in BP. The aims of this study were to evaluate, in older subjects, the comparative effects of intraduodenal glucose infusion, at a rate similar to GE of oral glucose, on BP, HR, superior mesenteric artery (SMA) flow, and blood glucose. Eight healthy subjects (5 men, 3 women, age 66-75 yr) were studied on two occasions. On day 1, each subject ingested 300 ml of water containing 75 g glucose. GE was quantified by three-dimensional ultrasonography between time t = 0-120 min, and the rate of emptying (kcal/min) was calculated. On day 2, glucose was infused intraduodenally at the same rate as that on day 1. On both days, BP, HR, SMA flow, and blood glucose were measured. The mean GE of oral glucose was 1.3 +/- 0.1 kcal/min. Systolic BP (P < 0.01), SMA flow (P < 0.05), and blood glucose (P < 0.01) were greater and HR less (P < 0.01) after oral, compared with intraduodenal, glucose. There were comparable falls in diastolic BP during the study days (P < 0.01 for both). We conclude that the magnitude of the fall in systolic BP and rise in HR are less after oral, compared with intraduodenal, glucose, presumably reflecting the "protective" effect of gastric distension.