Dong S J, Hees P S, Huang W M, Buffer S A, Weiss J L, Shapiro E P
Division of Cardiology, Johns Hopkins University School of Medicine, Johns Hopkins Bayview Medical Center, Baltimore, Maryland 21224, USA.
Am J Physiol. 1999 Sep;277(3):H1053-60. doi: 10.1152/ajpheart.1999.277.3.H1053.
Shortening of oblique left ventricular (LV) fibers results in torsion. A unique relationship between volume and torsion is therefore expected, and the effects of load and contractility on torsion should be predictable. However, volume-independent behavior of torsion has been observed, and the effects of load on this deformation remain controversial. We used magnetic resonance imaging (MRI) with tagging to study the relationships between load and contractility, and torsion. In ten isolated, blood-perfused canine hearts, ejection was controlled by a servopump: end-diastolic volume (EDV) was controlled by manipulating preload parameters and end-systolic volume (ESV) by manipulating afterload using a three-element windkessel model. MRI was obtained at baseline, two levels of preload alteration, two levels of afterload alteration, and dobutamine infusion. An increase in EDV resulted in an increase in torsion at constant ESV (preload effect), whereas an increase in ESV resulted in a decrease in torsion at constant EDV (afterload effect). Dobutamine infusion increased torsion in association with an increase in LV peak-systolic pressure (PSP), even at identical EDV and ESV. Multiple regression showed correlation of torsion with preload (EDV), afterload (ESV), and contractility (PSP; r = 0.67). Furthermore, there was a close linear relationship between torsion and stroke volume (SV) and ejection fraction (EF) during load alteration, but torsion during dobutamine infusion was greater than expected for the extent of ejection. Preload and afterload influence torsion through their effects on SV and EF, and there is an additional direct inotropic effect on torsion that is independent of changes in volume but rather is force dependent. There is therefore potential for the torsion-volume relation to provide a load-independent measure of contractility that could be measured noninvasively.
左心室（LV）斜纤维缩短导致扭转。因此，预计容积与扭转之间存在独特关系，负荷和收缩性对扭转的影响应该是可预测的。然而，已经观察到扭转存在与容积无关的行为，负荷对这种变形的影响仍存在争议。我们使用标记磁共振成像（MRI）来研究负荷、收缩性与扭转之间的关系。在10个离体、血液灌注的犬心脏中，射血由伺服泵控制：通过操纵前负荷参数控制舒张末期容积（EDV），使用三元风箱模型通过操纵后负荷控制收缩末期容积（ESV）。在基线、两个前负荷改变水平、两个后负荷改变水平以及多巴酚丁胺输注时获取MRI。在恒定ESV时，EDV增加导致扭转增加（前负荷效应），而在恒定EDV时，ESV增加导致扭转减少（后负荷效应）。即使在相同的EDV和ESV下，多巴酚丁胺输注也会随着左心室峰值收缩压（PSP）增加而增加扭转。多元回归显示扭转与前负荷（EDV）、后负荷（ESV）和收缩性（PSP；r = 0.67）相关。此外，在负荷改变期间，扭转与每搏输出量（SV）和射血分数（EF）之间存在密切的线性关系，但多巴酚丁胺输注期间的扭转大于根据射血程度预期的值。前负荷和后负荷通过对SV和EF的影响来影响扭转，并且存在对扭转的额外直接变力效应，该效应与容积变化无关，而是与力相关。因此，扭转 - 容积关系有可能提供一种与负荷无关的收缩性测量方法，这种方法可以无创测量。
