Stembridge Mike, Ainslie Philip N, Shave Rob
Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, UK.
Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Okanagan Campus, Kelowna, British Columbia, Canada.
Exp Physiol. 2015 Nov;100(11):1242-6. doi: 10.1113/expphysiol.2014.082503. Epub 2014 Nov 20.
What is the topic of this review? At high altitude, the cardiovascular system must adapt in order to meet the metabolic demand for oxygen. This review summarizes recent findings relating to short-term and life-long cardiac adaptation to high altitude in the context of exercise capacity. What advances does it highlight? Both Sherpa and lowlanders exhibit smaller left ventricular volumes at high altitude; however, myocardial relaxation, as evidenced by diastolic untwist, is reduced only in Sherpa, indicating that short-term hypoxia does not impair diastolic relaxation. Potential remodelling of systolic function, as evidenced by lower left ventricular systolic twist in Sherpa, may facilitate the requisite sea-level mechanical reserve required during exercise, although this remains to be confirmed. Both short-term and life-long high-altitude exposure challenge the cardiovascular system to meet the metabolic demand for O2 in a hypoxic environment. As the demand for O2 delivery increases during exercise, the circulatory component of oxygen transport is placed under additional stress. Acute adaptation and chronic remodelling of cardiac structure and function may occur to facilitate O2 delivery in lowlanders during sojourn to high altitude and in permanent highland residents. However, our understanding of cardiac structural and functional adaption in Sherpa remains confined to a higher maximal heart rate, lower pulmonary vascular resistance and no differences in resting cardiac output. Ventricular form and function are intrinsically linked through the left ventricular (LV) mechanics that facilitate efficient ejection, minimize myofibre stress during contraction and aid diastolic recoil. Recent examination of LV mechanics has allowed detailed insight into fundamental cardiac adaptation in high-altitude Sherpa. In this symposium report, we review recent advances in our understanding of LV function in both lowlanders and Sherpa at rest and discuss the potential consequences for exercise capacity. Collectively, data indicate chronic structural ventricular adaptation, with adult Sherpa having smaller absolute and relative LV size. Consistent with structural remodelling, cardiac mechanics also differ in Sherpa when compared with lowlanders at high altitude. These differences are characterized by a reduction in resting systolic deformation and slower diastolic untwisting, a surrogate of relaxation. These changes may reflect a functional cardiac adaptation that affords Sherpa the same mechanical reserve seen in lowlanders at sea level, which is absent when they ascend to high altitude.
本综述的主题是什么？在高海拔地区，心血管系统必须进行适应性变化，以满足对氧气的代谢需求。本综述总结了近期在运动能力背景下，关于短期和长期心脏对高海拔适应的研究发现。它突出了哪些进展？夏尔巴人和低地居民在高海拔地区的左心室容积都较小；然而，舒张期解旋所证明的心肌舒张功能，仅在夏尔巴人中降低，这表明短期缺氧不会损害舒张期舒张功能。夏尔巴人左心室收缩期扭转较低所证明的收缩功能的潜在重塑，可能有助于运动期间所需的海平面机械储备，尽管这仍有待证实。短期和长期的高海拔暴露都对心血管系统提出挑战，使其在缺氧环境中满足对氧气的代谢需求。随着运动期间对氧气输送需求的增加，氧气运输的循环部分会承受额外压力。在低地居民前往高海拔地区旅居期间以及永久居住在高海拔地区的居民中，心脏结构和功能可能会发生急性适应和慢性重塑，以促进氧气输送。然而，我们对夏尔巴人心脏结构和功能适应的理解仍局限于较高的最大心率、较低的肺血管阻力以及静息心输出量无差异。心室形态和功能通过左心室力学内在地联系在一起，左心室力学有助于有效射血、在收缩期间最小化肌纤维应力并辅助舒张期回弹。最近对左心室力学的研究，使我们能够深入了解高海拔夏尔巴人心脏的基本适应性变化。在本专题研讨会报告中，我们回顾了我们对低地居民和夏尔巴人静息时左心室功能理解的最新进展，并讨论了对运动能力的潜在影响。总体而言，数据表明存在慢性心室结构适应性变化，成年夏尔巴人的左心室绝对和相对大小较小。与结构重塑一致，与高海拔地区的低地居民相比，夏尔巴人的心脏力学也有所不同。这些差异的特征是静息收缩期变形减少和舒张期解旋减慢，舒张期解旋是舒张功能的一个指标。这些变化可能反映了一种功能性心脏适应，使夏尔巴人在海平面时具有与低地居民相同的机械储备，而当他们上升到高海拔时这种储备就不存在了。
