Pepi M, Guazzi M, Maltagliati A, Berna G, Tamborini G
Istituto di Cardiologia dell'Università degli Studi, Fondazione I. Monzino, IRCCS, Milan, Italy.
Clin Cardiol. 2000 Sep;23(9):665-72. doi: 10.1002/clc.4960230907.
The normal human heart behaves as a single functional unit during preload reduction; adaptations of the left ventricle to head-up tilting is mediated through ventricular interdependence and biventricular-lung interaction.
We hypothesized that reduction of venous return in dilated cardiomyopathy is likely to have a great effect on ventricular chamber geometry and filling. The aim of this study was to evaluate the effects of gradual head-up tilting in normal subjects and in patients with dilated cardiomyopathy, addressing special attention to right (RV) and left ventricular (LV) dimensions, geometry, and filling, and to biventricular-lung interaction.
Twenty normal subjects and 23 patients with moderate heart failure due to dilated cardiomyopathy were studied with two-dimensional and Doppler echocardiography in supine position and after 20 degrees, 40 degrees, and 60 degrees tilting. Right ventricular and LV dimensions, LV geometry, and tricuspid, mitral, and pulmonary venous flow patterns were recorded at each step of the study. Geometric changes of the LV were evaluated by measurements of volumes and diameters in the apical four-chamber view (which identifies the interventricular septum and lateral wall) and apical two-chamber view (which identifies the inferior and anterior wall of the LV).
In the two groups, tilting was associated with reduction of RV area and LV diameter and volumes; percent variations in LV diameter and volumes recorded in four-chamber view were lower at each step of tilting than with those derived from the two-chamber view in controls and in patients. In normal subjects, mitral and tricuspid peak early flow velocities were decreased at any tilting level; peak late velocities were unchanged; peak velocity of systolic forward flow of the pulmonary vein was reduced, diastolic forward flow was unchanged, and the difference in duration between reverse pulmonary flow and forward mitral A wave was reduced. Doppler findings were qualitatively similar in patients, but tilting induced a more marked redistribution of LV filling to late diastole because of a significant increase in atrial contribution.
Preload reduction by tilting induces profound effects on left and right dimensions, geometry, and filling in normal and dilated heart; reduction or RV dimensions are associated with changes in LV ventricular geometry (minimal reduction in septal-lateral diameter, marked reduction in anterior-posterior diameter), redistribution of right and left diastolic filling to late diastole, and redistribution of pulmonary venous flow to early diastole. These mechanisms are probably due to a favorable interaction between heart and lungs, which increases compliance within the pericardial space and facilitates redistribution of flow from the lungs. Even a minimal amount of preload reduction causes more marked effects in LV filling patterns in dilated cardiomyopathy than in normal hearts, confirming that ventricular interaction and pericardial constraint are increased when heart volume enlarges.
在减少前负荷期间，正常人体心脏作为一个单一的功能单元发挥作用；左心室对头高位倾斜的适应是通过心室相互依赖和双心室-肺相互作用介导的。
我们假设扩张型心肌病患者静脉回流减少可能对心室腔几何形状和充盈有很大影响。本研究的目的是评估正常受试者和扩张型心肌病患者逐渐头高位倾斜的影响，特别关注右心室（RV）和左心室（LV）的尺寸、几何形状和充盈情况，以及双心室-肺相互作用。
对20名正常受试者和23名因扩张型心肌病导致中度心力衰竭的患者进行了二维和多普勒超声心动图检查，检查在仰卧位以及倾斜20度、40度和60度后进行。在研究的每个阶段记录右心室和左心室尺寸、左心室几何形状以及三尖瓣、二尖瓣和肺静脉血流模式。通过在心尖四腔心切面（可识别室间隔和侧壁）和心尖两腔心切面（可识别左心室下壁和前壁）测量容积和直径来评估左心室的几何变化。
在两组中，倾斜与右心室面积、左心室直径和容积的减少有关；在每个倾斜阶段，四腔心切面记录的左心室直径和容积的百分比变化均低于对照组和患者组两腔心切面得出的变化。在正常受试者中，任何倾斜水平下二尖瓣和三尖瓣的早期血流峰值速度均降低；晚期峰值速度不变；肺静脉收缩期正向血流峰值速度降低，舒张期正向血流不变，肺静脉反向血流与二尖瓣A波正向血流持续时间的差异减小。患者的多普勒检查结果在性质上相似，但由于心房贡献显著增加，倾斜导致左心室充盈更明显地重新分布到晚舒张期。
通过倾斜减少前负荷对正常心脏和扩张型心脏的左右尺寸、几何形状和充盈有深远影响；右心室尺寸减小与左心室几何形状变化（室间隔-侧壁直径最小减小，前后直径显著减小）、左右舒张期充盈重新分布到晚舒张期以及肺静脉血流重新分布到舒张早期有关。这些机制可能是由于心脏与肺之间的有利相互作用，增加了心包腔内的顺应性并促进了肺内血流的重新分布。即使是最小量的前负荷减少，在扩张型心肌病中对左心室充盈模式的影响也比正常心脏更明显，证实当心脏容积增大时心室相互作用和心包约束增加。
