Wyle Science, Technology and Engineering Group, Houston, Texas, USA.
Am J Physiol Heart Circ Physiol. 2013 Apr 15;304(8):H1114-23. doi: 10.1152/ajpheart.00391.2012. Epub 2013 Feb 8.
Spaceflight-induced orthostatic intolerance has been studied for decades. Although ∼22% of the astronaut corps are women, most mechanistic studies use mostly male subjects, despite known sex differences in autonomic control and postflight orthostatic intolerance. We studied adrenergic, baroreflex, and autonomic indexes during continuous infusions of vasoactive drugs in men and women during a 60-day head-down bed rest. Volunteers were tested before bed rest (20 men and 10 women) and around day 30 (20 men and 10 women) and day 60 (16 men and 8 women) of bed rest. Three increasing doses of phenylephrine (PE) and sodium nitroprusside were infused for 10 min after an infusion of normal saline. A 20-min rest period separated the phenylephrine and sodium nitroprusside infusions. Autonomic activity was approximated by spectral indexes of heart rate and blood pressure variability, and baroreflex sensitivity was measured by the spontaneous baroreflex slope. Parasympathetic modulation and baroreflex sensitivity decreased with bed rest, with women experiencing a larger decrease in baroreflex sensitivity by day 30 than men. The sympathetic activation of men and parasympathetic responsiveness of women in blood pressure control during physiological stress were preserved throughout bed rest. During PE infusions, women experienced saturation of the R-R interval at high frequency, whereas men did not, revealing a sex difference in the parabolic relationship between high-frequency R-R interval, a measurement of respiratory sinus arrhythmia, and R-R interval. These sex differences in blood pressure control during simulated microgravity reveal the need to study sex differences in long-duration spaceflight to ensure the health and safety of the entire astronaut corps.
航天飞行引起的直立不耐受已经研究了几十年。尽管约 22%的宇航员是女性，但大多数机械性研究主要使用男性受试者，尽管自主控制和飞行后直立不耐受方面存在明显的性别差异。我们在 60 天的头低位卧床期间，研究了男女在连续输注血管活性药物期间的肾上腺素能、压力反射和自主神经指数。志愿者在卧床休息前（20 名男性和 10 名女性）和卧床休息第 30 天（20 名男性和 10 名女性）和第 60 天（16 名男性和 8 名女性）进行了测试。在输注生理盐水后，用苯肾上腺素（PE）和硝普钠钠进行 10 分钟的输注。PE 和硝普钠钠输注之间用 20 分钟的休息期隔开。自主神经活动通过心率和血压变异性的谱指数近似，通过自发压力反射斜率测量压力反射敏感性。随着卧床休息，自主神经活动和压力反射敏感性下降，女性在第 30 天的压力反射敏感性下降幅度大于男性。在生理应激期间，男性的交感神经激活和女性的血压控制的副交感神经反应在整个卧床休息期间都得到了保留。在 PE 输注期间，女性在高频时出现 RR 间隔饱和，而男性则没有，这揭示了高频 RR 间隔与 RR 间隔之间的抛物线关系（一种呼吸窦性心律失常的测量）存在性别差异。在模拟微重力期间，血压控制方面的这些性别差异揭示了需要研究长期太空飞行中的性别差异，以确保整个宇航员队伍的健康和安全。
