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，女性在站立时（即站立压力）血压下降幅度更大，从而导致昏厥或头晕眼花的症状。虽然确切的原因尚不清楚，但男性和女性对压力源的不同心血管反应，以及整个月经周期，可能起着作用。重要的是，呼吸、二氧化碳和氧气都可以影响心血管功能，但月经周期或药物雌激素和黄体酮（如口服避孕药（OC））对直立姿势时这些测量的影响从未被研究过。本研究项目的主要目的是确定性别和女性性激素（自然循环雌激素和孕激素或OC）对心血管、呼吸和自主神经对运动、直立姿势、高或低O2或高CO2的反应的影响。将特别强调呼吸、脑血流量和血液激素变化的测量，因为这些之前没有被研究过。这项工作将调查处于月经周期两个阶段的年轻女性，早期卵泡期（即雌激素和黄体酮水平低）和黄体期（即雌激素和黄体酮水平高），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。口服避孕药可以是环状的（即在所有药丸中使用高孕酮替代品，同时增加雌激素替代品的水平）或非环状的（即在整个周期中使用高雌激素替代品的所有药丸中使用高孕酮替代品）。目的1：比较自主神经平衡（即交感神经（战斗或逃跑）和副交感神经（休息和消化）对心血管系统的控制之间的平衡）和在握力锻炼、运动后循环闭塞、被动肢体运动或仰卧和直立姿势的化学感受器刺激/抑制（即高或低的O2或CO2）期间通过身体的血液流动。目的2：通过血流介导扩张（FMD）测量，确定性别和女性性激素对血管内皮功能的作用。口蹄疫将在仰卧位和直立位进行。对于这两个目标，女性将在月经周期的早期卵泡/低激素阶段和黄体/高激素阶段进行研究。本研究将调查自主神经、心血管和呼吸系统对生理应激源的反应，以及这些反应因性别和/或女性性激素而发生的变化。此外，这项工作是研究对这些压力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更高的原因提供以前未知的见解。

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.