Cheng C P, Igarashi Y, Little W C
Section of Cardiology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, N.C. 27103.
Circ Res. 1992 Jan;70(1):9-19. doi: 10.1161/01.res.70.1.9.
At rest, most of left ventricular (LV) filling occurs early in diastole. This LV filling occurs in response to the pressure gradient produced as LV pressure falls below left atrial (LA) pressure. Because mitral valve flow occurs in response to an LA to LV pressure gradient, augmented diastolic mitral valve flow during exercise may be due to an increased mitral valve pressure gradient resulting from a rise in LA pressure and/or a fall in LV early diastolic pressure. Accordingly, we studied 13 conscious dogs, instrumented to measure micromanometer LV and LA pressures, and determined LV volume from three ultrasonic dimensions during exercise. The animals ran on a treadmill for 8-15 minutes at 5-8 miles/hr. With reflexes intact, during exercise, the heart rate increased from 116 +/- 20 to 189 +/- 24 beats per minute (mean +/- SD, p less than 0.01), the maximum rate of change of LV volume (dV/dtmax) increased from 185 +/- 44 to 282 +/- 76 ml/sec (p less than 0.01), the ejection fraction and cardiac output increased, and the duration of diastole decreased from 296 +/- 83 to 162 +/- 71 msec (p less than 0.01). Mitral valve opening pressure, mean LA pressure (10.9 +/- 4.4 versus 10.2 +/- 3.9 mm Hg, p = NS), and LV end-diastolic pressure (12.8 +/- 4.8 versus 13.1 +/- 3.3 mm Hg, p = NS) were all relatively unchanged. The time constant of the fall of isovolumic LV pressure decreased from 28 +/- 3.3 to 21 +/- 4.4 msec (p less than 0.05). The early diastolic portion of the LV pressure-volume loop was shifted downward during exercise, with the minimum LV pressure decreasing from 3.3 +/- 2.8 to -2.8 +/- 3.4 mm Hg (p less than 0.05) and the maximum mitral valve pressure gradient increasing from 5.5 +/- 1.7 to 11.8 +/- 3.5 mm Hg (p less than 0.01). A similar downward shift of the early diastolic portion of the LV pressure-volume loop was produced by infusion of dobutamine (6 micrograms/kg/min i.v.) at rest, as well as by exercise when the heart rate was held constant by right ventricular pacing at 190-210 beats per minute. The downward shift during exercise was prevented by beta-blockade (metoprolol, 0.5 mg/kg i.v.). We conclude that during exercise, sympathetic stimulation and tachycardia produce a downward shift of the early diastolic portion of the LV pressure-volume loop.(ABSTRACT TRUNCATED AT 400 WORDS)
静息时，左心室（LV）的大部分充盈发生在舒张早期。这种左心室充盈是对左心室压力低于左心房（LA）压力时产生的压力梯度的反应。由于二尖瓣血流是对左心房到左心室的压力梯度的反应，运动期间舒张期二尖瓣血流增加可能是由于左心房压力升高和/或左心室舒张早期压力下降导致二尖瓣压力梯度增加。因此，我们研究了13只清醒犬，通过仪器测量微测压计的左心室和左心房压力，并在运动期间根据三个超声维度确定左心室容积。这些动物在跑步机上以5-8英里/小时的速度跑8-15分钟。在反射完整的情况下，运动期间，心率从每分钟116±20次增加到189±24次（平均值±标准差，p<0.01），左心室容积的最大变化率（dV/dtmax）从185±44增加到282±76毫升/秒（p<0.01），射血分数和心输出量增加，舒张期持续时间从296±83毫秒减少到162±71毫秒（p<0.01）。二尖瓣开放压力、平均左心房压力（10.9±4.4对10.2±3.9毫米汞柱，p=无显著性差异）和左心室舒张末期压力（12.8±4.8对13.1±3.3毫米汞柱，p=无显著性差异）均相对未改变。等容左心室压力下降的时间常数从28±3.3毫秒减少到21±4.4毫秒（p<0.05）。运动期间，左心室压力-容积环的舒张早期部分向下移位，左心室最小压力从3.3±2.8毫米汞柱降至-2.8±3.4毫米汞柱（p<0.05），最大二尖瓣压力梯度从5.5±1.7毫米汞柱增加到11.8±3.5毫米汞柱（p<0.01）。静息时静脉注射多巴酚丁胺（6微克/千克/分钟）以及通过右心室起搏将心率维持在每分钟190-210次时运动，均可产生左心室压力-容积环舒张早期部分类似的向下移位。运动期间的向下移位可通过β受体阻滞剂（美托洛尔，0.5毫克/千克静脉注射）预防。我们得出结论，运动期间，交感神经刺激和心动过速会使左心室压力-容积环舒张早期部分向下移位。（摘要截短至400字）
