In humans subjected to intense exercise, the splanchnic blood flow is reduced to about 40% (Kjòr et al. 1993) or even as low as 20% of the resting value (Rowell, 1973). Such a substantial reduction in blood flow is not associated with symptoms of abdominal hypoperfusion, which contrasts with patients suffering abdominal angina in whom the splanchnic blood flow is reduced to only 84% of rest (0·98 vs. 1·17 l min¢ in a control group; Buchardt Hansen et al. 1977). Therefore, we hypothesized that the exercise-induced reduction in splanchnic blood flow primarily follows a decrease in the hepato-splenic flow, while the mesenteric circulation remains relatively stable. In contrast to our hypothesis, Qamar & Read (1987) noted a 43 % reduction in the superior mesenteric artery (SMA) blood flow after treadmill exercise. However, Eriksen & Waaler (1994) reported a maintained SMA flow after fasting and postprandial short-duration (4 min) cycling, corroborating observations during submaximal exercise in the dog (Herrick et al. 1940;Van Citters & Franklin, 1969;Vatner, 1975). To evaluate these contradictory results, we assessed splanchnic blood flow (SBF) during fasting and postprandial exercise in healthy volunteers by both Indocyanine Green dye-elimination (dye-elimination) and duplex ultrasound techniques, which permitted separation of the hepato-splenic from the mesenteric circulations. METHODSNineteen healthy non-medicated and non-smoking volunteers aged 28 years (range, 24-35 years), 1·82 m (1·73-1·91 m) tall and weighing 81 kg (57-85 kg) participated in the study after informed consent and approval by the Ethics Committee for Medical Research in Copenhagen (Reg. no. KA 91192). The first ten subjects underwent fasting duplex ultrasound examination of the SMA and 1. Exercise reduces splanchnic blood flow, but the mesenteric contribution to this response is uncertain. 2. In nineteen humans, superior mesenteric and coeliac artery flows were determined by duplex ultrasonography during fasting and postprandial submaximal cycling and compared with the splanchnic blood flow as assessed by the Indocyanine Green dye-elimination technique. 3. Cycling increased arterial pressure, heart rate and cardiac output, while it reduced total vascular resistance. These responses were not altered in the postprandial state. During fasting, cycling increased mesenteric, coeliac and splanchnic resistances by 76, 165 and 126%, respectively, and it reduced corresponding blood flows by 32, 50 and 43% (by 0·18 ± 0·04, 0·42 ± 0·03 and 0·60 ± 0·04 l min¢). Postprandially, mesenteric and splanchnic vascular resistances decreased, thereby elevating regional blood flow, while the coeliac circulation was not influenced. Postprandial cycling did not influence the mesenteric resistance significantly, but its blood flow decreased by 22% (0·46 ± 0·28 l min¢). Coeliac and splanchnic resistance increased by 150 and 63%, respectively, and the corresponding regional blood flow decreased by 51 and 31% (0·49 ± 0·07 and 0·96 ± 0·28 l min¢). Splanchnic blood flow va...

We evaluated whether the increase in blood lactate with intense exercise is influenced by a low hepatosplanchnic blood flow as assessed by indocyanine green dye elimination and blood sampling from an artery and the hepatic vein in eight men. The hepatosplanchnic blood flow decreased from a resting value of 1.6 +/- 0.1 to 0.7 +/- 0.1 (SE) l/min during exercise. Yet the hepatosplanchnic O2 uptake increased from 67 +/- 3 to 93 +/- 13 ml/min, and the output of glucose increased from 1.1 +/- 0.1 to 2.1 +/- 0.3 mmol/min (P < 0.05). Even at the lowest hepatosplanchnic venous hemoglobin O2 saturation during exercise of 6%, the average concentration of glucose in arterial blood was maintained close to the resting level (5.2 +/- 0.2 vs. 5.5 +/- 0.2 mmol/l), whereas the difference between arterial and hepatic venous blood glucose increased to a maximum of 22 mmol/l. In arterial blood, the concentration of lactate increased from 1.1 +/- 0.2 to 6.0 +/- 1.0 mmol/l, and the hepatosplanchnic uptake of lactate was elevated from 0.4 +/- 0.06 to 1.0 +/- 0.05 mmol/min during exercise (P < 0.05). However, when the hepatosplanchnic venous hemoglobin O2 saturation became low, the arterial and hepatosplanchnic venous blood lactate difference approached zero. Even with a marked reduction in its blood flow, exercise did not challenge the ability of the liver to maintain blood glucose homeostasis. However, it appeared that the contribution of the Cori cycle decreased, and the accumulation of lactate in blood became influenced by the reduced hepatosplanchnic blood flow.

The present study shows a small but critical increase in Rout with increased patient age. A notable residual variation was present and borderline values of Rout should be regarded and used with caution.