Tethering resulted in vertebral wedging while maintaining spinal flexibility. Although changes in proteoglycan synthesis, collagen type distribution, and disc thickness were observed, the tethered discs had similar water content to control discs and did not demonstrate gross morphologic signs of degeneration. Growth modulation is an attractive treatment option for growing patients with scoliosis, avoiding multilevel fusions or brace wear. Strategies for fusionless scoliosis correction should preserve disc health, as adolescent patients will rely on these discs for decades after treatment.
The effects of exercise conditioning on the myocardium were studied in seven instrumented pigs strenuously exercised for 12 wk by treadmill running. Data were compared with eight instrumented untrained pigs. O2 consumption measured during maximum exercise effort was significantly elevated in the trained pigs (71.7 +/- 4.0 vs. 56.3 +/- 3.0 ml X ml-1 X kg-1). Absolute right and left ventricular mass increased by 20 and 13%, respectively, in response to exercise. Myocyte cross-sectional area increased by 21% in the trained hearts compared with the untrained hearts. Transmural left ventricular myocardial blood flow (ml X min-1 X g-1) was not significantly different at rest, during maximum exercise, or during exercise with adenosine infusion. However, training caused an elevation of the regional epicardial blood flow noted during exercise and exercise with adenosine. In the trained pigs mean aortic pressure during maximum exercise with adenosine infusion was not significantly different compared with untrained pigs. Coronary resistance during exercise with adenosine infusion was the same in both animal groups. In the trained group capillary numerical (no./mm2) and length (mm/mm3) densities were reduced, whereas arteriolar numerical and length densities were significantly increased compared with the untrained group. Measurements of capillary luminal surface density (mm2/mm3) in the trained group were unchanged compared with the untrained group. These results suggest that strenuous exercise does not stimulate the production of new capillaries, but this is modified by the ability of existing capillaries to increase their luminal surface area to parallel increases in myocyte growth. The arteriolar data suggest that exercise promotes the formation of new arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of chronic pressure overload hypertrophy on myocardial blood flow and capillary density was measured in the feline left ventricle. Myocardial hypertrophy was produced by and 84% banding constriction of the ascending aorta 2.8 +/- 1.2 months before the experiments. In seven cats with aortic constriction, cardiac hypertrophy produced a 40% increase in left ventricular mass. Seven cats served as normals. Our findings show that, in chronic pressure overload hypertrophy, coronary blood flow at control (resting) levels is increased compared with normals. In both normal and hypertrophy cats endocardial/epicardial flow ratios were equal at the control level. In the hypertrophied hearts, coronary reserve, measured as the percentage increase in myocardial blood flow from control to near maximal flow during adenosine infusion, was reduced. In the hypertrophy group a shift in the transmural distribution of blood flow in the left ventricle was noticed, as indicated by a reduced endo/epi flow ratio, during adenosine infusion. A decreased capillary density in hypertrophy, most marked in endocardial tissue regions, was demonstrated by this study. These findings indicate that capillary growth does not parallel myofibre growth in the endocardium of pressure overload hypertrophied left ventricles. The resultant anatomical imbalance causes a compromise of flow reserve in the endocardium, making this region vulnerable to ischaemia.
The effects of thyroxine-stimulated hypertrophy (TSH) were studied in the porcine left ventricular myocardium. Hypertrophy was produced in six adult pigs by administration of triiodothyronine (1 mg/kg; i.v.) for eight days. Six pigs served as controls. The degree of hypertrophy, determined by left ventricular-to-body weight ratio, was 47%. With hypertrophy there was a significant increase in heart rate, blood pressure and myocardial blood flows. Minimal coronary resistance measured during adenosine infusion was lower in the TSH group compared with the control group. Anatomic studies revealed a balanced proliferative response of mitochondria, myofibrils and the t-tubular system during TSH. Analysis of the microvasculature indicated that the capillary and arteriolar beds both experienced growth which paralleled myocyte growth during TSH. These results suggest that thyroxine administration promotes angiogenesis in the microvascular bed which provides a partial anatomic rationale for the lowered minimal coronary resistance.
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