Myocardial transcapillary exchange in the hypertrophied heart of the dog.

Myocardial transcapillary exchange was investigated in control hearts and in two types of hypertrophied hearts: exercise hypertrophy and pathological hypertrophy due to tricuspid insufficiency. Using the single-injection indicator diffusion method (6, 28), myocardial extractions (E), capillary clearances (C), and permeability surface area products (PS) of urea, sucrose, and inulin were measured in intact, pump-perfused, working hearts of anesthetized dogs. Both types of cardiac hypertrophy were associated with a decreased coronary vascular resistance. Myocardial E, C, and PS values from the exercised group were not significantly different from control. Dogs with pathological hypertrophy exhibited increased central venous pressures, RVEDP's, and heart rates which were greater than control values. The E, C, and PS values from the pathologically hypertrophied hearts were significantly greater than control. These increases in myocardial transcapillary exchange can be explained either by increasing the equivalent pore radius of myocardial capillary membranes from a control value of 70 to 100 A or by assuming that pathologically hypertrophied hearts have a myocardial capillary surface area available for exchange which is twice that of control hearts.