Pawelczyk J A, Zuckerman J H, Blomqvist C G, Levine B D
Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Am J Physiol Heart Circ Physiol. 2001 May;280(5):H2230-9. doi: 10.1152/ajpheart.2001.280.5.H2230.
Cardiovascular deconditioning reduces orthostatic tolerance. To determine whether changes in autonomic function might produce this effect, we developed stimulus-response curves relating limb vascular resistance, muscle sympathetic nerve activity (MSNA), and pulmonary capillary wedge pressure (PCWP) with seven subjects before and after 18 days of -6 degrees head-down bed rest. Both lower body negative pressure (LBNP; -15 and -30 mmHg) and rapid saline infusion (15 and 30 ml/kg body wt) were used to produce a wide variation in PCWP. Orthostatic tolerance was assessed with graded LBNP to presyncope. Bed rest reduced LBNP tolerance from 23.9 +/- 2.1 to 21.2 +/- 1.5 min, respectively (means +/- SE, P = 0.02). The MSNA-PCWP relationship was unchanged after bed rest, though at any stage of the LBNP protocol PCWP was lower, and MSNA was greater. Thus bed rest deconditioning produced hypovolemia, causing a shift in operating point on the stimulus-response curve. The relationship between limb vascular resistance and MSNA was not significantly altered after bed rest. We conclude that bed rest deconditioning does not alter reflex control of MSNA, but may produce orthostatic intolerance through a combination of hypovolemia and cardiac atrophy.
心血管失适应会降低直立耐力。为了确定自主神经功能的变化是否可能产生这种影响，我们绘制了7名受试者在 -6度头低位卧床休息18天前后，肢体血管阻力、肌肉交感神经活动（MSNA）和肺毛细血管楔压（PCWP）之间的刺激-反应曲线。使用下体负压（LBNP；-15和-30 mmHg）和快速输注生理盐水（15和30 ml/kg体重）来使PCWP产生广泛变化。通过分级LBNP至接近晕厥来评估直立耐力。卧床休息分别将LBNP耐力从23.9±2.1分钟降低至21.2±1.5分钟（平均值±标准误，P = 0.02）。卧床休息后，MSNA-PCWP关系未改变，尽管在LBNP方案的任何阶段，PCWP较低，而MSNA较高。因此，卧床休息失适应导致血容量不足，使刺激-反应曲线上的工作点发生偏移。卧床休息后，肢体血管阻力与MSNA之间的关系未显著改变。我们得出结论，卧床休息失适应不会改变MSNA的反射控制，但可能通过血容量不足和心脏萎缩共同作用导致直立不耐受。
