Monga Manoj, Macias Brandon, Groppo Eli, Kostelec Monica, Hargens Alan
Department of Urologic Surgery, University of Minnesota, 1420 Delaware Street, Minneapolis, MN 55455, USA.
J Urol. 2006 Jul;176(1):127-31. doi: 10.1016/S0022-5347(06)00572-6.
Prolonged exposure to microgravity during spaceflight causes metabolic changes that increase the risk of renal stone formation. Studies during the Gemini, Apollo, Skylab and Shuttle missions demonstrated alterations in renal function, fluid homeostasis and bone resorption that result in increased urinary supersaturation of calcium oxalate, brushite, sodium urate and uric acid. Developing countermeasures to increased urinary supersaturation is an important priority as the duration of space missions increases.
A total of 11 sets of identical twins remained on 6-degree head down, tilt bed rest for 30 days to simulate prolonged microgravity. One twin per pair was randomly selected to exercise while supine in a lower body negative pressure chamber 6 days weekly for 40 minutes, followed by 5 minutes of resting lower body negative pressure at 50 mm Hg. The other twin served as a nonexercise control. Pressure in the exercise lower body negative pressure chamber (52 to 63 mm Hg) was adjusted to produce footward forces equivalent to those for upright running on Earth at 1.0 to 1.2 x body weight. Pre-bed rest urinary stone risk profiles were done elsewhere after 5 days of a standardized diet, consisting of 170 mEq sodium, 1,000 mg calcium, 0.8 gm/kg animal protein and 2,500 kcal, and then throughout the bed rest and recovery phases of the protocol.
A significant increase in urinary calcium after just 1 week of bed rest was noted in the nonexercise control group (p = 0.001). However, no such increase was noted in the exercise group. Brushite supersaturation increased significantly from bed rest in each group, although the increase was significantly higher in the nonexercise control group than in the exercise group (p = 0.006). Calcium oxalate supersaturation increased during bed rest in the exercise group (p = 0.004). It trended toward a higher level in the nonexercise control group, although this did not achieve significance (p = 0.055) Mean urine volume +/- SD was significantly higher in the nonexercise control group than in the exercise group at bed rest week 2 and at week 3 (2.01 +/- 0.21 vs 1.63 0.18 l and 2.03 +/- 0.22 vs 1.81 +/- 0.20, respectively). Urinary pH was significantly higher in the nonexercise control group than in the exercise group at week 1 and week 3 (6.62 +/- 0.7 vs 6.49 +/- 0.5 and 6.58 +/- 0.6 vs 6.49 +/- 0.8, respectively, p = 0.01).
Bed rest significantly alters the urinary environment to favor calculous formation. Lower body negative pressure chamber treadmill exercise offers some protection against increases in stone risk during simulated microgravity, particularly with regard to the risks of hypercalciuria and brushite stone formation. The use of lower body negative pressure to augment aerobic exercise in space may decrease the risk of stone formation in astronauts. Adjunct measures, including aggressive hydration and alkalinization therapy, should be considered.
太空飞行期间长时间暴露于微重力环境会导致代谢变化，增加肾结石形成的风险。在双子座、阿波罗、天空实验室和航天飞机任务期间的研究表明，肾功能、体液平衡和骨吸收发生改变，导致草酸钙、透钙磷石、尿酸钠和尿酸的尿过饱和度增加。随着太空任务持续时间的增加，制定应对尿过饱和度增加的对策是一项重要的优先事项。
总共11对同卵双胞胎保持6度头低位，倾斜卧床休息30天以模拟长时间微重力环境。每对双胞胎中随机选择一人在每周6天的时间里，于下体负压舱内仰卧锻炼40分钟，随后在50毫米汞柱的下体负压下休息5分钟。另一对双胞胎作为非锻炼对照组。锻炼下体负压舱内的压力（52至63毫米汞柱）进行调整，以产生相当于在地球上以1.0至1.2倍体重进行直立跑步时的向足部力。在标准化饮食（包括170毫当量钠、1000毫克钙、0.8克/千克动物蛋白和2500千卡热量）5天后，在其他地方进行卧床休息前的尿结石风险评估，然后在整个卧床休息和方案的恢复阶段进行评估。
非锻炼对照组在卧床休息仅1周后尿钙显著增加（p = 0.001）。然而，锻炼组未观察到此类增加。每组透钙磷石过饱和度从卧床休息开始均显著增加，尽管非锻炼对照组的增加显著高于锻炼组（p = 0.006）。锻炼组在卧床休息期间草酸钙过饱和度增加（p = 0.004）。非锻炼对照组有升高趋势，尽管未达到显著水平（p = 0.055）。在卧床休息第2周和第3周时，非锻炼对照组的平均尿量+/-标准差显著高于锻炼组（分别为2.01 +/- 0.21对1.63 +/- 0.18升和2.03 +/- 0.22对1.81 +/- 0.20）。在第1周和第3周时，非锻炼对照组的尿pH值显著高于锻炼组（分别为6.62 +/- 0.7对6.49 +/- 0.5和6.58 +/- 0.6对6.49 +/- 0.8，p = 0.01）。
卧床休息显著改变尿液环境，有利于结石形成。下体负压舱跑步机锻炼对模拟微重力期间结石风险增加提供了一定保护，特别是在高钙尿症和透钙磷石结石形成风险方面。在太空中使用下体负压来增强有氧运动可能会降低宇航员结石形成的风险。应考虑采取辅助措施，包括积极的水化和碱化治疗。
