Do changes in gastro-intestinal blood flow explain high-altitude anorexia?

P>Background Gastrointestinal symptoms are common on acute exposure to high-altitude (HA). Underlying mechanisms are not understood, but vascular shunting away from the gut could be responsible. Therefore, blood flow in the superior mesenteric artery (SMA) and hepatic portal vein (HPV) was examined at sea level (SL) and after ascent to 4392 m (HA). Materials and methods Twelve subjects [eight male, mean age 40 (22-72) years] were studied following an overnight fast and a standard meal. Cross-sectional vessel area and blood velocity were measured by ultrasound, systolic and diastolic flow calculated for the SMA (HR x vessel area x velocity, cm3 min-1) and mean flow for the HPV. Results All subjects experienced reduced appetite at HA. Blood flow in the SMA and HPV increased following food at SL (mean SMA systolic flow 1024 vs. 3316 cm3 min-1, P < 0 center dot 001; HPV 505 vs. 1789, P < 0 center dot 001) and at HA (2020 vs. 3767, P < 0 center dot 001; HPV 708 vs. 1727, P < 0 center dot 001). Pre-prandial flow in the SMA and HPV was significantly increased at HA compared with SL. The changes were due to increased vessel diameter and increased flow velocity. There was no difference in post-prandial flow between SL and HA in the HPV, although the increase in post-prandial flow was greater at SL than HA (254% increase vs. 144%). Conclusions These results show that resting blood flow in the gastrointestinal tract is increased during exposure to high-altitude hypoxia, and that the vascular response of increased blood flow following food ingestion is maintained. Therefore, reduced flow is unlikely to cause gastrointestinal symptoms and reduced appetite at HA.