[Digestive system's large and changing needs of blood supply]

Area of Science:

• Physiology
• Gastroenterology
• Cardiovascular Science

Background:

• Doppler ultrasonography allows direct, continuous measurement of digestive tract blood flow (superior mesenteric artery) in conscious humans.
• Previous studies indicate post-meal increases in blood flow to the digestive tract, varying with meal size.

Purpose of the Study:

• To investigate human digestive tract blood flow and cardiac output responses to meals and exercise.
• To compare human responses to those observed in animal models.

Main Methods:

• Utilizing Doppler ultrasonography to monitor superior mesenteric artery blood flow.
• Observing changes in blood flow and cardiac output in healthy humans after consuming meals of varying sizes (carbohydrates, protein, fat).
• Assessing digestive tract blood flow during high-intensity physical exercise in the postprandial state.

Main Results:

• Meals cause a gradual, marked increase in digestive tract blood flow, peaking at 20-40 minutes and lasting 1.5-2 hours.
• Both local blood flow and cardiac output increase post-meal, regardless of meal composition (carbohydrates, protein, fat).
• Contrary to animal studies, high-intensity exercise does not reduce digestive tract blood flow in humans; post-meal cardiac output increases are additive to exercise-induced increases.

Conclusions:

• Meals impose a significant workload on the heart by increasing both digestive tract blood flow and overall cardiac output.
• Human digestive tract blood flow is resilient to exercise, even in the postprandial state.
• The combined cardiovascular demands of meals and exercise may explain increased angina pectoris symptoms after eating.