The aortic roots of 3 heparinized mongrel dog hearts were cannulated and connected to a perfusion system. Tyrode's solution was infused to remove intracoronary blood and was followed by 3% cacodylate-buffered glutaraldehyde with added adenosine for 15 minutes. The entire procedure was performed at a perfusion pressure of 90 mm Hg with ventricular fibrillation, a vented left ventricle, and maximal coronary vasodilatation produced by adenosine. These conditions result in a reproducible, minimal level of extravascular and intravascular coronary resistance. Full wall-thickness tissue samples were taken from the regions of the anterior (APM) and posterior (PPM) papillary muscles. These samples were divided into 3 transmural layers, termed subendocardial (ENDO), intermediate (INT), and subepicardial (EPI). Electron microscopy was employed for capillary quantitation due to the high resolution requirements. All morphometric data were corrected for fixation shrinkage. 6 tissue blocks (2 mm3) were randomly selected from each of the 6 primary sample sites in each heart. Half of the blocks were cut perpendicular to the myofiber direction, with the remainder cut at a 90° angle to the first cut. 4 randomly selected fields were evaluated per section, with sampling sufficient to give a 95% confidence interval of ≤±10% of the mean. Data comparison between ENDO and EPI layers suggest that capillaries in the ENDO layer are less numerous, have a greater diameter, and are separated by a greater distance. ENDO layer capillaries appear to have a slightly larger volumetric density but a smaller surface density than the EPI layer. Measurements of arithmetic mean wall thickness show a thicker capillary wall in the ENDO layer compared to EPI. These preliminary data imply a transmural gradient in maximal oxygen diffusion capacity, with the ENDO layer at a disadvantage compared to the EPI layer. These structural features are consistent with the clinically noted predilection of the ENDO layer to ischemia and infarction.
|Original language||English (US)|
|Number of pages||2|
|State||Published - 1980|
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