A simple cutter for fresh tissue to facilitate the investigation of intramyocardial blood flow with tracer microspheres in cats and rabbits.

Tracer microspheres (TM) allow the measurement of regional tissue blood flow. For this purpose the tissue must be cut into the regions selected for measurements. We describe a simple tissue cutter, that greatly facilitates accurate and reproducible cutting of fresh tissue. We have demonstrated its usefulness for obtaining measurements of myocardial blood flow in different layers of the left ventricular free wall of hearts of anesthetized cats and conscious rabbits. Since complete trapping of the TM is essential for blood flow measurements by this method, we investigated the minimal TM size needed by comparing results obtained with different size microspheres. 25 and 15 micrometer TM were trapped equally well by all layers of the left ventricle, but TM smaller than 15 micrometers were not trapped completely. From the size distribution of the 7-10 micrometer TM, we estimated that the functional diameter of the largest capillaries was somewhat smaller (about 7.6 micrometer) in the subepicardial (epi) than in the subendocardial (endo) layer (7.9 micrometer) in both species. When measured with 15 micrometer TM, intramyocardial distribution of blood flow was comparable to that reported for dogs and sheep. In open chest cats, the endo/epi ratio was 1.25 and 1.28, and in conscious rabbits it was 1.35. We conclude that TM with diameters between 10 and 15 micrometers are suitable for measuring intramyocardial blood flow in cats' and rabbits' hearts, and that unlike in dogs and sheep, 7-10 micrometer TM cannot be used.