Cerebrovascular and ventilatory responses to autonomic reflex stimulation in supine and upright postures in women throughout the menstrual cycle and men

众所周知，与男性相比，女性站立时的血压下降幅度更大(即立位压力)，从而导致晕厥或头晕和头晕的症状。尽管确切的原因尚不清楚，但男性和女性之间以及整个月经周期对应激源的不同心血管反应可能起到了作用。重要的是，呼吸、二氧化碳和氧气都可以影响心血管功能，但在直立姿势时，月经周期或药物雌激素和孕酮(如口服避孕药(OC))对这些测量的影响从未被研究过。本研究计划的主要目的是确定性激素和女性性激素(自然循环雌激素和孕激素或OC)对锻炼、直立姿势、高或低O2或高二氧化碳时心血管、呼吸和自主神经反应的影响。将特别强调对呼吸、脑血流量和血液激素变化的测量，因为这些以前从未被研究过。这项工作将调查处于月经周期两个阶段的年轻女性，即早期卵泡阶段(即雌激素和黄体酮水平较低)和黄体期(即雌激素和黄体酮水平都较高)，以及年龄匹配的男性。不同类型的OC也将被调查，服用OC的妇女将在安慰剂周和最大剂量周进行测试。OC既可以是周期性的(即在所有雌激素替代品水平增加的药丸中替代高孕酮)，也可以是非周期性的(即在整个周期中，所有替代雌激素水平较高的药丸都是高孕酮替代品)。目的1：比较手握力运动、运动后循环闭塞、被动肢体运动或化学感受器刺激/抑制(高或低O2或CO2)时的自主神经平衡(即交感神经(战斗或逃跑)和副交感神经(休息和消化)对心血管系统控制的平衡)和通过身体的血流量。目的2：通过血流介导的扩张法(FMD)确定性别和女性性激素对血管内皮功能的作用。FMD将在仰卧位和直立位进行。出于这两个目的，我们将研究处于月经周期的早期卵泡/低激素阶段和黄体/高激素阶段的女性。这项研究将调查自主神经、心血管和呼吸对生理应激源的反应，以及这些反应由于性和/或女性性激素的变化。此外，这项工作是研究对这些应激源反应背后的血管机制的重要一步，并将为女性站立时低血压发生率较高的原因提供以前不为人知的见解。

Women are known to have a greater drop in blood pressure upon standing (i.e. orthostatic stress) compared to men leading to fainting or symptoms of lightheadedness and dizziness. Although the exact reasons for this are unclear, different cardiovascular responses to stressors between men and women, and throughout the menstrual cycle, likely play a role. Importantly, breathing, CO2, and O2 each can impact cardiovascular function yet the influence of the menstrual cycle or pharmaceutical estrogen and progesterone (such as oral contraceptives (OC)) on these measurements during upright posture has never been investigated.The main objective of this research program is to determine the effects of sex and female sex hormones (natural cycling estrogen and progesterone or OC) on the cardiovascular, respiratory and autonomic nervous responses to exercise, upright posture, high or low O2, or high CO2. There will be a specific emphasis on measurements of breathing, brain blood flow, and changes in blood hormones as these have not previously been investigated. This work will investigate young women in two phases of the menstrual cycle, the early follicular phase (i.e. estrogen and progesterone are low) and the luteal phase (i.e. both estrogen and progesterone are high), and age-matched men. Different types of OC will also be investigated and women taking OC will be tested during the placebo week and the maximal dose week. OC can be either cyclic (i.e. high progesterone substitute in all pills with increasing levels of estrogen substitute) or non-cyclic (i.e. high progesterone substitute in all pills with high estrogen substitute throughout the cycle). Aim #1: To compare autonomic balance (i.e. balance between sympathetic (fight or flight') and parasympathetic (rest and digest') control of the cardiovascular system) and blood flow through the body during handgrip exercise, post-exercise circulatory occlusion, passive limb movement, or chemoreceptor stimulation/inhibition (i.e. high or low O2 or CO2) in the supine and upright postures.Aim #2: To determine the role of sex and female sex hormones on vascular endothelial function via flow-mediated dilation (FMD) measurements between all groups of men and women. FMD will be conducted in the supine and upright positions. For both Aims, women will be studied in the early follicular/low hormone phase and the luteal/high hormone phase of the menstrual cycle.This research will investigate autonomic, cardiovascular, and respiratory responses to physiological stressors and the changes in those responses due to sex and/or female sex hormones. Further, this work is an essential step to investigating the vascular mechanisms behind the responses to these stressors, and will provide previously unknown insight into the reasons for greater incidence of low blood pressure during standing in women.