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• W4251941303 abstract "Extract: This report describes the in vitro analysis of the series elasticity of ventricular myocardium isolated from five fetal lambs and six adult sheep. Active compliance measurements were obtained by quick releases utilizing a closed loop servosystem and electromagnetic positioning device to control cardiac muscle length or tension. Right ventricular moderator bands were obtained from five fetuses (average 139 days of gestation, term = 147 days), and compared with two adult moderator bands and four adult right ventricular trabeculae carneae. After correction for equipment coupling, the experimental load extension data were fit to an exponential expression by a least squares technique: strain = l/b ln (l + stress/a). When fetal and adult data were compared, no age-related differences in the constants were observed (a = 0.185 ± 0.062 SE (fetal) and 0.159 ± 0.03g/mm2 (adult); b = 40.4 ± 5.2 (fetal) and 43.1 ± 5.2 (adult); and ab = 7.39 ± 2.34 (fetal) and 5.27 ± .99 (adult). However, significant variation existed in the histologically determined amount of contractile tissue present in muscle samples from both fetus (57-85%, average = 74.0 ± 4.9) and adult (64-94%, average = 82.3 ± 5.3). Without regard to age, a significant correlation was found between the b stiffness constant and the amount of contractile mass present in cardiac muscle. Thus, it is concluded that there is no age-related difference in the stiffness of fetal and adult ventricular muscle. However, there is a significant relationship between active compliance and true muscle mass. Speculation: There is now substantial evidence that isometric force generation in fetal ventricular myocardium is significantly depressed when compared with the adult (3). Moreover, this reduction in the strength of cardiac contraction is not accompanied by a comparable depression in the extrapolated or unloaded velocity of shortening when fetal and adult hearts are compared (3). Several hypotheses have been advanced to explain the depression of force generation in fetal tissue. First, it is clear that there is less contractile tissue per unit volume in fetal myocardium (3, 13); second, a depression of contractile state may exist in fetal cardiac muscle (3). Although the additional contractile tissue present in the adult heart could explain the lesser force generation of fetal myocardium, it is also possible that a more compliant “series elasticity” in fetal muscle could be responsible for an attenuation of force generation, particularly since the unloaded velocities are similar in the two groups of muscle. Indeed, the resting length-tension relationship of fetal muscle (3) and the non-normalized pressure-volume relationship of the whole heart (7, 13) have been shown to be significantly “stiffer” than in adult preparations, although the resting stiffness per unit mass of tissue may not be altered (7). Accordingly, the present study was designed to examine the active compliance of fetal and adult sheep myocardium in order to determine whether age-related differences exist in “series elasticity” or active stiffness." @default.
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• W4251941303 date "1976-07-01" @default.
• W4251941303 modified "2023-09-26" @default.
• W4251941303 title "A Comparison of the Active Stiffness of Fetal and Adult Cardiac Muscle" @default.
• W4251941303 doi "https://doi.org/10.1203/00006450-197610070-00006" @default.
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