Yin F C, Weisfeldt M L, Milnor W R
J Clin Invest. 1981 Jul;68(1):28-38. doi: 10.1172/jci110245.
The diminished cardiac output response to exercise with advancing age may be attributable to intrinsic inability of the old ventricle to respond appropriately and/or to an additional loading imposed upon the ventricle by the aged vascular system. The steady (resistance) and pulsatile (characteristic impedance) load components together comprise the vascular load faced by the ejecting ventricle. To study the effect of exercise on both vascular components of load, the aortic input impedance was measured in chronically instrumented young and old beagle dogs during graded treadmill exercise before and after beta blockade. Ascending aortic flow was measured by a cuff electromagnetic flow probe, and pressure was measured by a high-fidelity semiconductor transducer. At low levels of exercise the old animals demonstrated a striking 20% increase in characteristic impedance and a 28% decrease in peripheral resistance with no increase in stroke volume. This vascular loading and limitation in stroke volume persisted across the higher exercise levels. In contrast, the young group demonstrated no increase in characteristic impedence, a progressive decrease in peripheral resistance, and a progressive increase in stroke volume across the same exercise levels. These age differences in vascular response and ventricular output were abolished by beta blockade. The groups did not demonstrate a difference in heart rate response, but the young had a greater increase in external left ventricular power than the old across exercise. These data demonstrated a profound difference in the response of young and old vasculature to exercise. At low and intermediate exercise levels the pulsatile vascular load appeared to be a major factor in the limitation of stroke volume in old dogs. At high levels of exercise, the limited exercise response in the old dog may be caused in part by a diminished inotropic responsiveness as well as by the vascular loading.
随着年龄增长，心脏对运动的输出反应减弱，这可能归因于老年心室自身无法做出适当反应和/或老年血管系统给心室增加的负荷。稳定（阻力）和搏动（特征阻抗）负荷成分共同构成了射血心室所面临的血管负荷。为了研究运动对负荷的两个血管成分的影响，在分级跑步机运动前后，对长期植入仪器的年轻和老年比格犬在β受体阻滞剂给药前后测量主动脉输入阻抗。升主动脉血流通过袖带电磁流量探头测量，压力通过高保真半导体换能器测量。在低运动水平时，老年动物的特征阻抗显著增加20%，外周阻力降低28%，而每搏量没有增加。这种血管负荷和每搏量的限制在较高运动水平时持续存在。相比之下，年轻组在相同运动水平下特征阻抗没有增加，外周阻力逐渐降低，每搏量逐渐增加。β受体阻滞剂消除了这些血管反应和心室输出方面的年龄差异。两组在心率反应上没有差异，但在整个运动过程中，年轻组左心室外部功率的增加幅度大于老年组。这些数据表明年轻和老年血管系统对运动的反应存在深刻差异。在低和中等运动水平时，搏动性血管负荷似乎是老年犬每搏量受限的主要因素。在高运动水平时，老年犬有限的运动反应可能部分是由于心肌收缩反应性降低以及血管负荷所致。
