MacGowan G A, Burkhoff D, Rogers W J, Salvador D, Azhari H, Hees P S, Zweier J L, Halperin H R, Siu C O, Lima J A, Weiss J L, Shapiro E P
Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA.
Cardiovasc Res. 1996 Jun;31(6):917-25.
To determine if left ventricular torsion, as measured by magnetic resonance tissue tagging, is afterload dependent in a canine isolated heart model in which neurohumoral responses are absent, and preload is constant.
In ten isolated, blood perfused, ejecting, canine hearts, three afterloads were studied, while keeping preload constant: low afterload, high afterload (stroke volume reduced by approx. 50% of low afterload), and isovolumic loading (infinite afterload).
There were significant effects of afterload on both torsion (P < 0.05) and circumferential shortening (P < 0.0005). Between low and high afterloads, at the anterior region of the endocardium only, where torsion was maximal, there was a significant reduction in torsion (15.1 +/- 2.2 degrees to 7.8 +/- 1.8 degrees, P < 0.05). Between high afterload and isovolumic loading there was no significant change in torsion (7.8 +/- 1.8 degrees to 6.2 +/- 1.5 degrees, P = NS). Circumferential shortening at the anterior endocardium was significantly reduced both between low and high afterload (-0.19 +/- 0.02 to -0.11 +/- 0.02, P < 0.0005), and also between high afterload and isovolumic loading (-0.11 +/- 0.02 to 0.00 +/- 0.02, P < 0.05). Plots of strains with respect to end-systolic volume demonstrated a reduction in both torsion and shortening with afterload-induced increases in end-systolic volume. Torsion, but not circumferential shortening, persisted at isovolumic loading.
Maximal regional torsion of the left ventricle is afterload dependent. The afterload response of torsion appears related to the effects of afterload on end-systolic volume.
在无神经体液反应且前负荷恒定的犬离体心脏模型中，通过磁共振组织标记测量左心室扭转，确定其是否依赖于后负荷。
在10个离体、血液灌注、有射血功能的犬心脏中，研究了三种后负荷情况，同时保持前负荷恒定：低后负荷、高后负荷（每搏量减少约低后负荷的50%）和等容负荷（无限后负荷）。
后负荷对扭转（P < 0.05）和圆周缩短（P < 0.0005）均有显著影响。在低后负荷和高后负荷之间，仅在心内膜的前部区域（此处扭转最大），扭转有显著降低（从15.1±2.2度降至7.8±1.8度，P < 0.05）。在高后负荷和等容负荷之间，扭转无显著变化（从7.8±1.8度至6.2±1.5度，P =无显著性差异）。在心内膜前部，低后负荷和高后负荷之间圆周缩短显著减少（从-0.19±0.02降至-0.11±0.02，P < 0.0005），高后负荷和等容负荷之间也显著减少（从-0.11±0.02至0.00±0.02，P < 0.05）。关于收缩末期容积的应变图显示，随着后负荷诱导的收缩末期容积增加，扭转和缩短均减少。在等容负荷时扭转持续存在，但圆周缩短不存在。
左心室最大区域扭转依赖于后负荷。扭转的后负荷反应似乎与后负荷对收缩末期容积的影响有关。
