GENDER & AGE EFFECTS ON ORTHOSTATIC TOLERANCE AFTER SHORT TERM BED REST

以前的研究表明，卧床休息或太空飞行会改变血管张力的调节。有证据表明，在卧床休息的同时解除心血管疾病会导致直立性低血压，而卧床休息4-6小时后就会出现这种情况。本研究的主要目的是确定短期(6小时)头低位倾斜床休息对立位时心血管功能的影响，并研究年龄(20-40岁和40-60岁)和性别对这些观察的影响。我们正在监测血压、心电图、多普勒(用于测量主动脉每搏出血量、脑血流量和股动脉血流量)、小腿围、呼吸频率。二氧化碳含量和腓肠肌交感神经(显微神经学检查)。受试者首先将头部向上倾斜70度，持续20分钟，然后头部向下倾斜6度，持续6个小时，最后进行第二次头部向上倾斜测试。

Previous studies have shown that regulation of blood vessel tone is altered by bed rest or following space flight. Evidence suggests that cardiovascular deconditioning with bed rest results in orthostatic hypotension and that this can develop after only 4-6 hours of bed rest. The key objectives of this study are to determine the effect of short term (6 hour) head down tilt bed rest on cardiovascular function during orthostasis and to study the effect of age (20-40 and 40-60 years) and gender on these observations. We are monitoring blood pressure, ECG, Doppler (for measurement of aortic stroke volume, cerebral blood flow and femoral artery blood flow), calf circumference, respiratory rate. CO2 content and peroneal nerve muscle sympathetic tome (microneurography). The subject will be initially tilted 70 degrees head-up for 20 minutes followed by a 6 degree head down tilt for 6 hours and finally a second head-up tilt test.