Merits and pitfalls in morphological assessment of cardiac growth.

The basic principles of quantitative morphological analysis of myocardial tissue are presented. Particular attention is paid to the effects of stimulated cardiac growth on the relationship between cell size and various indices of myocardial capillary supply in pressure-overloaded rat hearts. The importance of adequate sampling and of the number of measurements is stressed with respect to reliable estimation of the mean values but even more for assessment of variability of the measured data. When estimating myocardial capillary supply by average values of capillary density and/or of areas supplied by a single capillary, this crucial information is missing. Therefore the merits of more advanced techniques allowing for the estimation of variability of capillary spacing are critically examined and the significance of their application to myocardial tissue is outlined (method of concentric circles and method of triangular nets). Finally, the importance of variability of capillary spacing on oxygen supply is demonstrated. The variability of capillary spacing alone may affect oxygen supply independently of the average values of intercapillary distance.