Loshbaugh, Jenny E., Jack A. Loeppky, and E. Richard Greene. Effects of acute hypobaric hypoxia
on resting and postprandial superior mesenteric artery blood flow. High Alt. Med. & Biol. 7:47–53,
2006.—Reduced blood flow to the gut may contribute to weight loss and gastrointestinal symptoms
of acute mountain sickness (AMS) at altitude. A study in humans tested the hypothesis that acute
hypobaric hypoxia (ALT) would attenuate the normal postprandial hyperemia in the superior
mesenteric artery (
SM). Blood pressure, cardiac output (CO), and
SM were measured with previously validated noninvasive Doppler ultrasonic flowmetry in 9 (3 women) healthy young adults (mean age: 23; range: 18–33 yr) residing at 1700 m. Baseline measurements were made after 2 h at
ALT in a chamber at 430 mmHg (≍4800 m = 15,750 ft) after 10–12-h fasting, and the next day the
control (CON) measurements were made at 615 mmHg (1850 m). Postprandial measurements were
made 45 to 60 min after ingesting a 1000-cal liquid meal under both conditions. At ALT, 5 of the 9
subjects had AMS by the Lake Louise score criteria of headache ≥1 and total score ≥3. ALT significantly
reduced fasting, baseline
SM relative to CON by 15%, and increased CO by 16%. The
postprandial CO increase was not different between ALT and CON, but
SM increased 115% at CON, but only 75% at ALT, the attenuation being significant (p < 0.006). Neither the diminution of
fasting
SM at ALT nor the attenuation of the postprandial increase in
SM correlated significantly with AMS symptom scores. These results suggest that baseline and postprandial gut blood flow are altered during acute altitude exposure because of increased intestinal sympathetic tone, inferred
from increased local resistance, and may be related to reduced energy intake if sustained during
prolonged exposure.
