Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, United Kingdom.
Am J Physiol Heart Circ Physiol. 2011 Aug;301(2):H478-87. doi: 10.1152/ajpheart.00314.2011. Epub 2011 May 13.
During incremental exercise, stroke volume (SV) plateaus at 40-50% of maximal exercise capacity. In healthy individuals, left ventricular (LV) twist and untwisting ("LV twist mechanics") contribute to the generation of SV at rest, but whether the plateau in SV during incremental exercise is related to a blunting in LV twist mechanics remains unknown. To test this hypothesis, nine healthy young males performed continuous and discontinuous incremental supine cycling exercise up to 90% peak power in a randomized order. During both exercise protocols, end-diastolic volume (EDV), end-systolic volume (ESV), and SV reached a plateau at submaximal exercise intensities while heart rate increased continuously. Similar to LV volumes, two-dimensional speckle tracking-derived LV twist and untwisting velocity increased gradually from rest (all P < 0.001) and then leveled off at submaximal intensities. During continuous exercise, LV twist mechanics were linearly related to ESV, SV, heart rate, and cardiac output (all P < 0.01) while the relationship with EDV was exponential. In diastole, the increase in apical untwisting was significantly larger than that of basal untwisting (P < 0.01), emphasizing the importance of dynamic apical function. In conclusion, during incremental exercise, the plateau in LV twist mechanics and their close relationship with SV and cardiac output indicate a mechanical limitation in maximizing LV output during high exercise intensities. However, LV twist mechanics do not appear to be the sole factor limiting LV output, since EDV reaches its maximum before the plateau in LV twist mechanics, suggesting additional limitations in diastolic filling to the heart.
在递增运动过程中，每搏量（SV）在最大运动能力的 40-50%处达到平台期。在健康个体中，左心室（LV）扭转和解旋（“LV 扭转力学”）有助于在休息时产生 SV，但在递增运动过程中 SV 的平台期是否与 LV 扭转力学的钝化有关尚不清楚。为了检验这一假设，9 名健康年轻男性以随机顺序连续和不连续地进行仰卧位踏车递增运动，直至达到峰值功率的 90%。在两种运动方案中，舒张末期容积（EDV）、收缩末期容积（ESV）和 SV 在亚最大运动强度时达到平台期，而心率持续增加。与 LV 容积相似，二维斑点追踪衍生的 LV 扭转和解旋速度从休息时逐渐增加（均 P<0.001），然后在亚最大强度时趋于平稳。在连续运动中，LV 扭转力学与 ESV、SV、心率和心输出量呈线性相关（均 P<0.01），而与 EDV 的关系呈指数关系。在舒张期，心尖解旋的增加明显大于基底解旋（P<0.01），强调了动态心尖功能的重要性。总之，在递增运动过程中，LV 扭转力学的平台期及其与 SV 和心输出量的密切关系表明，在高运动强度下最大限度地提高 LV 输出存在机械限制。然而，LV 扭转力学似乎不是限制 LV 输出的唯一因素，因为 EDV 在 LV 扭转力学达到平台期之前达到最大值，这表明舒张期充盈到心脏的限制因素还有其他。
