Microsphere passage through intestinal circulation: via shunts or capillaries?

Area of Science:

• Physiology
• Biomedical Engineering
• Microcirculation Research

Background:

• Intracardiac or intra-arterial injection of 9-micron microspheres results in 20-30% appearing in venous blood.
• Previous hypotheses suggested non-capillary shunts facilitate microsphere passage, but capillary diameter overlap is also a factor.

Purpose of the Study:

• To develop probabilistic models predicting microsphere passage through capillaries.
• To determine if capillary passage adequately explains microsphere presence in venous blood.
• To assess the utility of microsphere distribution for estimating intestinal capillary diameters.

Main Methods:

• Development of probabilistic models based on microsphere diameter and capillary size independence.
• Injection of 9-micron microspheres and analysis of their presence in venous blood in canine models.
• Injection of a mixture of microspheres (5-20 micron) to observe sieving effects.

Main Results:

• Modeled passage through capillaries accurately predicted observed microsphere presence in canine intestinal circulation.
• Capillary passage (7.38 +/- 1.4 micron) sufficiently explained microsphere presence in venous blood.
• A mixture of microspheres demonstrated a significant sieving effect, validating the models.

Conclusions:

• Passage through intestinal capillaries, not shunts, accounts for 9-micron microspheres in venous blood.
• The frequency distribution of venous microspheres can serve as an in vivo method for estimating intestinal capillary diameter distribution.