Nutritional Needs in Hot Environments Applications for Military Personnel in Field Operations (1993) / Chapter Skim
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4. Effects of Excercise and Heat on Gastrointestinal Function
4. Effects of Excercise and Heat on Gastrointestinal Function
Pages 75-86
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From page 75... ...
Because most studies have not isolated the effects of high environmental or internal body temperature per se, the combined effects of exercise and heat stress are discussed. The questions to be addressed include the follow~ng: What GI symptoms are manifested during exercise-heat stress?
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From page 76... ...
IMPORTANCE OF GI MANIFESTATIONS WITH EXERCISE-HEAT STRESS Severe heat exposure simulates hemorrhage and intestinal ischemia because blood pools in the cutaneous capacitance vessels, central blood volume and splanchnic blood flow decline, and mean arterial pressure falls because increased heart rate cannot fully compensate for a declining stroke volume that causes cardiac output to fall. Hemorrhage and intestinal ischemia
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From page 77... ...
Mucosal biopsy specimens of the upper digestive track revealed histologically pathological features in all runners (Table 4-2~. These features included vascular lesions, ranging from congestion to hemorrhage, and evidence of reduced mucosal secretion (estimated from PAS [para-aminosalicylic acid]
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From page 78... ...
78 CARL V GISOLFI HYPOTHESIS EXHAUSTIVE EXERCISE O DECREASED SPLANCHNIC ^ BLOOD FLOW 1 INTESTINAL ISCHEMIA/ REPERFUSION ~ Gastrointestinal "Leak" 1 ENDOTOXEMIA Clinical Manifestations of Heat Stroke FIGURE 4-1 Flow diagram showing hypothesized mechanisms of endotoxemia and thermal injury associated with exercise-heat stress.
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From page 79... ...
GASTRIC EMPTYING Is there any evidence that environmental temperature, or a rise in core body temperature, adversely affects the rate at which the stomach empties? The observation that gastric emptying (GE)
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From page 80... ...
These investigators also found that hypohydration significantly reduced GE. The mechanism responsible for this reduction is unclear, but it is probably related to the thermal strain associated with hypohydration and exercise-heat stress.
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From page 81... ...
If gastrids or upper GI ulceration is the source of GI symptoms, therapy with antacids or H2 blockers may provide relief and allow soldiers to function normally. · When GI symptoms do occur as a result of exercise per heat stress, they usually abate quickly (within days)
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From page 82... ...
Infusion began at time 0. Negative values indicate absorption.
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From page 83... ...
Blake 1988 Strenuous exercise causes systemic endotoxemia.
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From page 84... ...
Lundgren 1973 The effects of vasoconstrictor fibre stimulation on consecutive vascular sections of cat small intestine during hemorrhagic hypotension. Acta Physiol.
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From page 85... ...
I think it is important that over at least a 90-minute period of intense exercise, we had one subject reach a core temperature of 40°C and observed no reduction in intestinal absorption of either active or passive solutes nor did we observe any change in fluid absorption. If you exceed 90 minutes of strenuous exercise, especially if it is performed in a warm environment, I don't know the consequences on the GI tract.
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