胸内正压对正常人左室功能影响及其力学原理

目的：探讨胸内正压对正常人左室射血及充盈的影响及其力学原理。方法：超声心动图观测30例正常人初始时与标准乏氏动作张力期10s时左室舒张末容积（LVEDV）、左室收缩末容积（LVESV）、每搏量（SV）、射血分值（EF）、流入道血流速度（E峰、A峰）、E／A值、二尖瓣环舒张早期运动速度（e）及舒张早期充盈压（E/e）的变化。结果：与初始时比较，标准乏氏动作张力期LVEDV、LVESV及SV减低而心率（陬）增快（P均〈0．001），EF值增加，但无统计学意义（P〉0．05）；E峰与E／A值减低（P均〈O．05）；e没有变化（P〉0．05）．E／e值减低（P〈O．05）。结论：胸内正压对左室游离壁的力学作用促进了左室收缩运动而阻碍了左室舒张运动，会引起EF值增加，E峰及E／A值减低；2，胸内正压降低了肺静脉系统与心脏的跨壁压力，增加了血流阻力也是导致肺静脉系统与左室血液回流减少．E峰减低．E／e值减低的一个原因。

Effectsof Positive Intrathoracic Pressure on Left Ventricular Ejection and Filling in Healthy Subjects and Its Mechanism

Our aim was to explore the mechanical effects of positive intrathoracic pressure on left ventricular （LV） ejection and filling in healthy subjects and its mechanism. Methods： 30 healthy volunteers were recruited to perform Valsalva maneuver （VM） at a load of 40 mm Hg lasted for 10 seconds. Parameters of LV function were determined by echoeardiography at rest and at 10th second during the strain phase of VM. Results： Compared to the rest, at 10th second, LV stroke volume （SV） dramatically decreased （P〈 0.001） while heart rate （HR） dramatically increased （P〈0.001）, and ejection fraction （EF） insignificantly increased （P〉0.05）; early diastolic velocity （E） significantly decreased （P〈0.05）, late diastolic velocity （A） insignificantly decreased （P〉0.05） and E/A ratio significantly decreased （P〈 0.05）; early diastolic velocity （e） of the mitral annulus did not changed （P 〉 0.05） and E/e ratio significantly decreased （P〈0.05）. Conclusions： Mechanical effects of positive intrathoracic pressure on LV free wall assist LV systolic motion while impede LV diastolic motion, which could cause the increase of EF while cause the decrease of E and E/A ratio. Positive intrathoraeic pressure increases the flow resistance of LV and pulmonary vasculature, which may contribute to the decrease of E and E/e ratio.