The Validity of the Indicator Dilution Method for Measuring the Capillary Diffusion Capacity for 51Cr‐EDTA in Hyperaemic Skeletal Muscle

Muscle capillary permeability to 51Cr‐EDTA was studied in the exercising forearm of 17 normal human adults. — The permeability data were obtained by means of the indicator dilution technique and the fractional unidirectional transcapillary loss or extraction, E, of 51Cr‐EDTA was calculated using five conceptually different equations. They all yielded practically the same E value. This supports the contention that the indicator dilution technique can give a valid measure of the permeability characteristics of the skeletal muscle capillary wall. These permeability characteristics are expressed as the capillary diffusion capacity, CDC, which is defined as the maximal unidirectional transcapillary flux of a permeable tracer per unit concentration difference per 100 g skeletal muscle. In normal man CDCCr‐EDTA reaches its maximum value of 3.95, SD ± 0.50 moles/100 g·min per mole/ml at plasma flow levels exceeding 15 ml/100g·min.