Michael M. Laks

Volumes and Compliances Measured Simultaneously in the Right and Left Ventricles of the Dog

In 10 normal dogs, the right and left ventricular volumes and compliances were determined in the fresh post-mortem heart. With the use of a Sigma Motor pump, Ringers solution at 23°C was simultaneously infused into both ventricles within an hour after death. When the ventricles were full but open to atmospheric pressure, the mean volumes were 35.8 ml/m2 for the right and 23.1 ml/m2 for the left ventricle; when the transmural pressure was increased by 10 mm Hg, the mean volumes were 56.9 ml/m2 for the right and 41.9 ml/m2 for the left ventricle; at 20 mm Hg, the values were 60.8 and 48.5 ml/m2, respectively. The initial volumes and the increases in volume produced by increase in transmural pressure were affected by the position of the ventricular septum and by the presence of rigor mortis. With infusions into only one ventricle, right and left ventricular volumes were 20 to 74% greater at 10 mm Hg than the values when both ventricles were filled simultaneously. Compliance began to decrease 40 to 60 min after death; at 130 min after death (23°C), the change in volume when the transmural pressure was increased to 10 mm Hg was only about 1/5 of that immediately after death.

Canine Right and Left Ventricular Cell and Sarcomere Lengths after Banding the Pulmonary Artery

Canine hearts were fixed with glutaraldehyde at zero transmural pressure 17 to 48 weeks after main pulmonary arterial banding. Tissues were taken from the trabeculae carneae at the ventricular right base, right apex, left base, and left apex. They were placed in osmium tetroxide, embedded in Epon 812, stained with Azure II methylene blue, and sectioned at ½ μ. The mean cell lengths of the hearts with main pulmonary arterial banding were greatest at the right base, 105±5 μ and left base, 103±5.7 μ. (The means ± SE are given.) The mean cell length at the left apex was 95±4 μ and that at the right apex was 92±5 μ. All were greater (P <0.001) than the cell lengths of normal hearts, 71±1.5 μ. The mean sarcomere lengths of the right ventricle with main pulmonary arterial banding (right base, 2.04±0.006 μ right apex, 2.18±0.004 μ) were less than those of normal hearts (right base, 2.41±0.006 μ right apex, 2.46±0.003 μ). The mean sarcomere length of the left base with main pulmonary arterial banding (2.10±0.01 μ) was less than the normal (2.16±0.002 μ); however, the mean sarcomere length of the left apex with main pulmonary arterial banding (2.28±0.005 μ) was the same as the normal. With main pulmonary arterial banding, both the right and left ventricular cell lengths increased more at the bases than at the apexes, and the sarcomere lengths decreased in the right base, right apex, and left base.

Presence of Widened and Multiple Intercalated Discs in the Hypertrophied Canine Heart

Fresh tissues were taken for light microscopy from the trabeculae carneae at the right ventricular base, apex, left ventricular base, and apex of four normal canine hearts and nine whose pulmonary artery had been banded for 7 to 48 weeks. After banding, the width of the intercalated disc at the right base, 1.34 ± 0.10 μ (mean ± SE), was greater than at the right apex, 1.02 ± 0.09 μ (P<0.002); both were greater than the normals (P<0.005 and P<0.001). The intercalated discs were wider than corresponding normals in only three hearts at the left base and six at the left apex. The mean widths of the discs correlated positively with both ventricular wall thickness and weight in the right ventricle but not in the left. Structures characterized by two, three, or four transverse segments of discs lying along the same myofibrils, each two of which are separated by 1 to 10 sarcomeres, have been named multiple intercalated discs. In six of the nine hearts whose pulmonary artery was banded, there were more multiple discs per mm2 at the right base and right apex than in the corresponding normals (P<0.02). In five of these, the number of multiple discs per mm2 was greater at the right base than in the corresponding apex (P<0.001). There was no significant increase in the number of multiple discs per mm2 in either the left base or left apex of the experimental animals compared to controls. After banding the pulmonary artery, tension increases in the right ventricle and this stimulates a broadening of the folds of the discs and then triggers a mechanism for the formation of new sarcomeres, perhaps involving multiple intercalated discs.

Time course of changes in the mechanical properties of the canine right and left ventricles during hypertrophy caused by pressure overload.

We developed a mathematical model of the right and left ventricles to determine whether there is a change in the mechanical properties of muscle during the hypertrophy process resulting from pulmonary arterial banding. Pressure-volume data were obtained from 10 normal dog hearts and 8 dog hearts in which the pulmonary artery was banded for periods of 2-40 weeks. These data were applied to the model, and the time course of wall stress and muscle stiffness was quantified for both ventricles. The results demonstrate that (1) myocardial stiffness is increased in pressure-overload hypertrophy (2) normal right and left ventricular muscle exhibits similar mechanical properties and(3) the relationships between wall stresses and the volume/mass ratios to the period of banding are biphasic. We concluded that (1) increase in muscle stiffness is due to several factors. In the early stages of hypertrophy, it may be predominantly due to fibrosis and, in the later stages, to substantial increases in muscle mass. (2) The progressive increase in muscle stiffness concomitant with the increase in muscle mass may be due to the presence of myocardial cellular projections and fibrosis. (3) The appropriate timing for surgical/medical intervention should take place before low volume: mass ratios and, hence, low wall stresses are attained. Circ Res 46: 530-542, 1980

Myocardial Cell and Sarcomere Lengths in the Normal Dog Heart

The purpose of this study was to measure myocardial cell and sarcomere lengths at the bases and apices of the right (RV) and left ventricle (LV) of 4 normal canine hearts. The RV and LV were simultaneously fixed with glutaraldehyde at zero transmural pressure. Sections of trabeculae carneae were taken from the 1 cm cut at the bases (free wall) of the RV and LV. They were further fixed with osmium tetroxide, embedded in Epon 812, sectioned at ½ to 1 μ and stained with azure II and methylene blue. Measured from photomicrographs (X 1,000) taken with the phase microscope, mean cell length was 70.9 μ±1.49 (SEM); no statistical difference existed between the cell lengths at the bases and apices of the RV and LV. From adjacent tissue, the measurements of sarcomere lengths made from photomicrographs (phase microscope, oil immersion lens, enlarged to X 4,000) were not statistically different from those made with the electron microscope (P>0.9). The sarcomere lengths at the LV base were the shortest−2.16 μ±0.002 (SEM), followed by the LV apex, 2.28 μ±0.005 (SEM); RV base, 2.41 μ±0.006 (SEM); and RV apex, 2.46 μ±0.003 (SEM). These variations in sarcomere length show the importance of specifying the site of sampling of myocardial tissue. The sarcomere lengths were related inversely to the thickness of the ventricular wall. This observation may be considered the structural reflection of the lesser distensibility of the left base as compared with the right apex, and may be simply the manifestation of the fact that the left base contains more muscle fibers.

Hyperpotassemia and Hypercalcemia

T HIS 74-YEAR-OLD W H I T E MAN HAD carcinoma of the bladder for four years. A few days prior to this electrocardiogram, he showed signs further substantiated by laboratory determinations consistent with urinary tract obstnrction. On the day this electrocardiogram was taken, the following laboratory findings were reported: potassium 7.4 mEq/L.; calcium 12 mg. per cent; CO, 23 mEq/L.; albumin 2.2 gm. per cent; globulin 3.8 gm. per cent; creatinine 6.5 mg. per cent; phasphorus 7 mg. per cent; pH 7.46; magnesium 2.95 mg. per cent; (1.7 to 2.7 mg. per cent). The patient expired two days later. Necropsy rwealed a normal heart.