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

Area of Science:

• Physiology
• Altitude Medicine
• Gastrointestinal Physiology

Background:

• Gastrointestinal symptoms are common during acute high-altitude (HA) exposure.
• Mechanisms remain unclear, with vascular shunting away from the gut a potential cause.
• This study investigated blood flow in the superior mesenteric artery (SMA) and hepatic portal vein (HPV) at sea level (SL) and HA.

Purpose of the Study:

• To examine the impact of high-altitude exposure on gastrointestinal blood flow.
• To determine if vascular shunting away from the gut contributes to symptoms at HA.
• To assess the gastrointestinal vascular response to food ingestion at HA.

Main Methods:

• Twelve subjects (8 male, mean age 40) were studied under fasted and post-meal conditions at SL and 4392 m.
• Ultrasound measured cross-sectional vessel area and blood velocity in the SMA and HPV.
• Blood flow was calculated for the SMA and HPV.

Main Results:

• All subjects reported reduced appetite at HA.
• Pre-prandial SMA and HPV blood flow were significantly increased at HA compared to SL, due to increased vessel diameter and flow velocity.
• Post-prandial blood flow increased at both SL and HA, with a greater percentage increase at SL.

Conclusions:

• Resting gastrointestinal blood flow is elevated during high-altitude hypoxia.
• The vascular response to food ingestion is maintained at HA.
• Reduced gastrointestinal blood flow is unlikely to be the cause of symptoms and appetite reduction at HA.