Richardson Russell S, Secher Niels H, Tschakovsky Michael E, Proctor David N, Wray D Walter
Department of Medicine, University of California San Diego, La Jolla, CA 92009, USA.
Med Sci Sports Exerc. 2006 Oct;38(10):1792-6. doi: 10.1249/01.mss.0000229568.17284.ab.
Unlike quadrupeds, human limbs are exposed to differing homeostatic challenges and uses. The arms are not exposed to a large hydrostatic pressure and contain a relatively small muscle mass that is not typically engaged in heavy work. In contrast, the legs have a large blood volume, experience significant hydrostatic pressures, and contain the majority of the body's muscle mass, which is used regularly to perform the significant work of locomotion. This raises the question of whether skeletal muscle blood flow and metabolism differ between limbs and whether these responses may be altered during exercise as a consequence of aging and disease. Initially, we examine the long standing question of how the body copes with the involvement of both sets of limbs and the large muscle mass that this entails, restrained by a finite cardiac output and a need to defend arterial blood pressure. We therefore evaluate the similarities and differences in exercising muscle blood-flow control in the upper and lower limbs, with respect to exercise onset kinetics, intrinsic vasoreactivity of the resistance vessels at rest and during exercise, and the role of gender and the aging process in limb-specific responses. It is concluded that blood flow and pressure when multiple limbs are simultaneously recruited is facilitated by sympathetically mediated vasoconstriction. Inherent limb differences, in terms of skeletal muscle metabolism and blood flow, do exist, and elucidating the mechanisms underlying limb-specific adaptations will be important for interpreting abnormal vascular function attributable to healthy aging and disease.
与四足动物不同，人类的四肢面临着不同的稳态挑战和用途。手臂不会承受较大的静水压力，且肌肉量相对较少，通常不从事繁重工作。相比之下，腿部血容量大，承受显著的静水压力，且包含身体大部分肌肉，这些肌肉经常用于进行重要的运动工作。这就引出了一个问题，即骨骼肌的血流和代谢在四肢之间是否存在差异，以及在运动过程中，这些反应是否会因衰老和疾病而改变。首先，我们研究一个长期存在的问题：身体如何应对两组肢体及其所包含的大量肌肉的参与，同时还要受限于有限的心输出量以及维持动脉血压的需求。因此，我们评估上肢和下肢在运动肌肉血流控制方面的异同，包括运动起始动力学、静息和运动时阻力血管的内在血管反应性，以及性别和衰老过程在肢体特异性反应中的作用。得出的结论是，当多个肢体同时参与运动时，交感神经介导的血管收缩有助于增加血流和血压。骨骼肌代谢和血流方面确实存在肢体固有差异，阐明肢体特异性适应的潜在机制对于解释健康衰老和疾病导致的异常血管功能至关重要。
