An "on-line" colorimetric method for repeated, rapid determinations of capillary diffusion capacity

Area of Science:

• Physiology
• Pharmacology

Background:

• The estimation of capillary diffusion capacity is crucial for understanding microvascular function.
• Existing methods like fractional venous sampling have limitations in reproducibility and frequency of measurement.

Purpose of the Study:

• To develop and validate a novel single injection indicator diffusion method for directly visualizing and continuously recording venous time-concentration curves.
• To enable frequent, controlled, and reproducible determinations of capillary diffusion capacity.

Main Methods:

• Utilized a two-colour densitometer system for continuous colorimetric recordings.
• Employed Cardio-Green (non-permeant tracer) and Cr-EDTA (permeant tracer) in an artificially perfused rat hindquarter muscle model.
• Obtained highly reproducible recordings every fourth minute.

Main Results:

• The developed method provides directly visualized, continuous colorimetric recordings of venous time-concentration curves.
• Highly reproducible curve recordings were achieved, with disturbances readily detected.
• The technique allows for immediate control and frequent repetition of capillary diffusion capacity determinations.

Conclusions:

• The single injection indicator diffusion method offers significant advantages over fractional venous sampling for assessing capillary diffusion capacity.
• This technique facilitates quantitative comparisons of capillary diffusion and filtration capacities under various physiological conditions.
• A key limitation is the requirement for erythrocyte-free perfusates due to the chosen permeant tracer.