Christ F, Gamble J, Baranov V, Kotov A, Gartside I, Nehring I, Messmer K
Institute of Anaesthesiology, Ludwig Maximilians University Munich, D-81366 Munich, Germany.
Eur J Med Res. 1999 Jul 28;4(7):264-70.
Orthostatic dysregulation is a frequent phenomenon in pilots experiencing extreme G forces and after prolonged exposures to microgravity in cosmonauts. We used non-invasive venous congestion plethysmography (VCP) to study microcirculatory changes and the ability to activate peripheral and centrally mediated protective mechanisms during various degrees of tilt, which we used as an orthostatic challenge.
The study, which was approved by the local ethical committee of the Institute of Biomedical Problems, was performed on six healthy 20 - 26 years old male volunteers. We applied 6 - 8 cumulative small venous congestion pressure steps (8 mmHg) to the thigh and determined the fluid filtration capacity (Kf), the linear relationship between cuff pressure (Pcuff) and measured fluid filtration (Jv). We then measured the fluid filtration (Jv) response to varying cumulative degrees of tilt, starting at 0 degrees followed by head down -8 degrees -15 degrees, -30 degrees -15 degrees, -8 degrees, 0 degrees, and then head up 15 degrees, 30 degrees, 70 degrees, 30 degrees, 15 degrees and 0 degrees. Each tilt stage was sustained for 15 minutes. The change in hydrostatic load, at the level of the strain gauge, was determined by measuring the difference in vertical height between the right atrium and mid calf at the level of the gauge. Limb arterial blood flow was measured and lung function tests were performed before and after the small cumulative pressure step protocol, as well as at the end of each tilt step.
No significant changes in blood pressure (BP) and heart rate (HR) occurred during the cumulative pressure step protocol. However, an increase in HR was observed during the tilt, but only reached significance at 30 degrees and 70 degrees. The mean Kf value measured with small cumulative pressure steps was 3.25 +/- 0.5 (10(-3) ml.100 ml tissue(-1) mmHg(-1) = KfU), which was significantly (p < 0.005) higher than the value obtained using tilt to increase the hydrostatic load (0.98 +/- 0.2 KfU). One subject had an unchanged Kf value and experienced vaso - vagal syncope following the imposition of 70 degrees tilt, with a heart rate < 35 / min and a systolic blood pressure of 60 mmHg. The measurement of blood flow in the limb showed no significant change during the tilt procedure. The lung function measurements revealed, that only expiratory reserve volume (ERV) did significantly increase during 35 degrees and 70 degrees head up tilt. All other parameters were unchanged. We suggest that the differences in these Kf values can be explained by the activation of both central and peripheral mediated changes in pre- capillary resistance in response to the tilt. We suspect, that the vaso - vagal syncope, experienced by one subject, reflected his inability to activate these protective reflex mechanisms, a situation that could be exacerbated by sub-clinical venous insufficiency. We believe that these results show that VCP is a useful tool for the determination of intolerance to orthostatic stress.
体位性调节障碍是飞行员在经历极端重力加速度以及宇航员长期暴露于微重力环境后常见的现象。我们使用无创静脉充血体积描记法（VCP）来研究微循环变化以及在不同程度倾斜过程中激活外周和中枢介导的保护机制的能力，我们将这种倾斜用作体位性应激试验。
本研究经生物医学问题研究所当地伦理委员会批准，对6名年龄在20 - 26岁的健康男性志愿者进行。我们对大腿施加6 - 8个累积的小静脉充血压力步骤（8 mmHg），并测定液体滤过能力（Kf）、袖带压力（Pcuff）与测得的液体滤过（Jv）之间的线性关系。然后我们测量了在不同累积倾斜度下的液体滤过（Jv）反应，起始倾斜度为0度，随后依次为头向下 -8度、-15度、-30度、-15度、-8度、0度，然后头向上15度、30度、70度、30度、15度和0度。每个倾斜阶段持续15分钟。通过测量应变计水平处右心房与小腿中部之间的垂直高度差，确定应变计水平处的静水压负荷变化。在累积小压力步骤方案前后以及每个倾斜步骤结束时，测量肢体动脉血流量并进行肺功能测试。
在累积压力步骤方案期间，血压（BP）和心率（HR）无显著变化。然而，在倾斜过程中观察到心率增加，但仅在30度和70度时达到显著水平。用累积小压力步骤测得的平均Kf值为3.25 +/- 0.5（10⁻³ ml·100 ml组织⁻¹ mmHg⁻¹ = KfU），显著高于（p < 0.005）通过倾斜增加静水压负荷获得的值（0.98 +/- 0.2 KfU）。一名受试者的Kf值未改变，在施加70度倾斜后发生血管迷走性晕厥，心率 < 35次/分钟，收缩压为60 mmHg。倾斜过程中肢体血流量测量无显著变化。肺功能测量显示，仅在头向上倾斜35度和70度时呼气储备量（ERV）显著增加。所有其他参数均未改变。我们认为这些Kf值的差异可以通过倾斜引起的前毛细血管阻力的中枢和外周介导变化的激活来解释。我们怀疑一名受试者经历的血管迷走性晕厥反映了他无法激活这些保护反射机制，这种情况可能因亚临床静脉功能不全而加剧。我们相信这些结果表明VCP是确定对体位性应激不耐受的有用工具。
