Davy K P, Seals D R, Tanaka H
Center for Physical Activity, Disease Prevention, and Aging, Department of Kinesiology, University of Colorado at Boulder, USA.
Hypertension. 1998 Aug;32(2):298-304. doi: 10.1161/01.hyp.32.2.298.
Based on observations of smaller increases in limb vascular resistance during acute incremental hypovolemia in older adults, cardiopulmonary and integrative (combined cardiopulmonary and arterial) baroreflex control of sympatho-circulatory function is thought to be impaired with aging in humans. We tested this hypothesis directly by making intraneural measurements of skeletal muscle sympathetic nerve activity (MSNA; peroneal microneurography) in groups of young (23+/-1 years; n=11) and older (64+/-1 years; n=12) healthy adult men during progressive hypovolemia produced by graded (-5 to -40 mm Hg) lower body negative pressure (LBNP). Baseline levels of MSNA and arterial blood pressure were higher and heart rate was lower in the older subjects (P<0.05). Lower levels of LBNP (-5 to -20 mm Hg) did not affect arterial blood pressure or heart rate in either group; systolic and pulse pressures declined during higher levels of LBNP (-30 and -40 mm Hg) but only in the young subjects (P<0.05). Graded LBNP evoked progressive, linear reductions in peripheral venous pressure (PVP) and increases in MSNA, plasma norepinephrine concentration (PNE), and forearm vascular resistance (FVR) in both groups (all P<0.05). DeltaMSNA/ deltaPVP was approximately 150% greater in the older versus young men during both lower and higher levels of hypovolemia (P<0.01); however, deltaFVR/deltaPVP was approximately 50% smaller in the older men (P<0.05). There was no difference in the MSNA-PNE relation with age, but deltaFVR/deltaMSNA was approximately 65% to 70% smaller in the older subjects (P<0.05). Our findings indicate that cardiopulmonary and integrative baroreflex control of central sympathetic outflow during hypovolemia is augmented, not impaired, with age in healthy humans. However, the reflex-mediated increases in limb vascular resistance during hypovolemia are smaller in older adults because of attenuated vasoconstrictor responsiveness to sympathetic stimulation.
基于对老年人急性渐进性血容量减少期间肢体血管阻力较小增加的观察，人们认为心肺和综合（心肺和动脉联合）压力反射对交感循环功能的控制在人类衰老过程中会受损。我们通过在年轻（23±1岁；n = 11）和老年（64±1岁；n = 12）健康成年男性组中，在分级（-5至-40 mmHg）下体负压（LBNP）导致的渐进性血容量减少期间，对骨骼肌交感神经活动（MSNA；腓骨微神经ography）进行神经内测量，直接检验了这一假设。老年受试者的MSNA和动脉血压基线水平较高，心率较低（P<0.05）。较低水平的LBNP（-5至-20 mmHg）对两组的动脉血压或心率均无影响；较高水平的LBNP（-30和-40 mmHg）期间收缩压和脉压下降，但仅在年轻受试者中出现（P<0.05）。分级LBNP在两组中均引起外周静脉压（PVP）逐渐线性降低，以及MSNA、血浆去甲肾上腺素浓度（PNE）和前臂血管阻力（FVR）增加（所有P<0.05）。在较低和较高水平血容量减少期间，老年男性与年轻男性相比，DeltaMSNA/DeltaPVP大约高150%（P<0.01）；然而，老年男性的DeltaFVR/DeltaPVP大约低50%（P<0.05）。MSNA与PNE的关系在年龄上没有差异，但老年受试者的DeltaFVR/DeltaMSNA大约低65%至70%（P<0.05）。我们的研究结果表明，在健康人类中，随着年龄增长，血容量减少期间心肺和综合压力反射对中枢交感神经流出的控制增强而非受损。然而，由于对交感神经刺激的血管收缩反应减弱，老年人在血容量减少期间反射介导的肢体血管阻力增加较小。
