Relation of ultrastructure and function. Sarcomere dimensions, pressure-volume curves, and geometry of the intact left ventricle of the immature canine heart.

Publisher Website
Google Scholar
Abstract
In 18 immature dogs (3-4 wk old) anesthetized with chloralose and morphine, the hearts were arrested with KCl and excised. After reproducible curves relating pressure and volume in the left ventricle (LV) were obtained, each LV was fixed by coronary perfusion with glutaraldehyde while pressure was maintained at a predetermined value between 0-30 mm Hg. Midwall sarcomere length in the LV free wall was determined by EM and related to fixation pressure to postfixation volume by silastic casts. Casts were also used to measure ventricular chamber dimensions. Results were compared with results for adult dogs. In the immature canine LV the relation of sarcomere length and pressure is similar to that of the adult dog at physiological pressures. Above 15 mm Hg sarcomeres resist stretch significantly with immature LV fixed between 15-30 mm Hg pressure with an average sarcomere length of 2.21 .+-. 0.05 .mu. in contrast to adult sarcomere length of 2.33 .+-. 0.01 .mu.m (P < 0.05). In the immature heart, EM demonstrated reduced cell size and evidence of assembly of immature sarcomeres from myofilaments. Compliance is reduced in the immature canine LV at pressures greater than 5 mm Hg as demonstrated in pressure-volume curves analyzed by exponential curve fitting. Measurements of silastic casts indicate a close geometric similarity between the immature and adult LV. Apparently the ultrastructural limits on performance are similar in the adult and immature canine LV; the latter LV may be better protected against damage from volume overloads.