ten Harkel A D, Baisch F, Karemaker J M
Department of Medicine, Univ. of Amsterdam Academic Medical Centre, Netherlands.
Acta Physiol Scand Suppl. 1992;604:89-99.
The effect of simulated weightlessness on orthostatic blood pressure regulation was evaluated with passive 70 degrees head-up tilt (HUT) after 10 days 6 degrees head-down tilt (HDT). Six healthy male volunteers were studied. Continuous recording of finger blood pressure (BP) was obtained non-invasively with a FinapresTM device. Instantaneous heart rate (HR) was derived from the electrocardiogram. To quantify orthostatic BP variability, a fast fourier transform (FFT) of the beat-by-beat BP- and RR-interval values was performed. Control HR before HUT after the 10-day HDT period was increased, probably due to an arousal state of the test subjects. The change in BP induced by HUT was not influenced by 10 days' HDT, in contrast to the HR rise which increased from 24 +/- 2 beats/min to 41 +/- 7 beats/min (P less than 0.05). After HDT the total variance in orthostatic BP almost doubled. FFT indicated that this increase in variance can be ascribed to BP oscillations with a frequency of around 0.1 Hz. In three subjects transient HR decelerations during HUT after HDT were observed. Analysis of the relationship between BP and HR in the transients showed that each HR decrease was preceded by a BP increase above normal. These HR decelerations seemed, therefore, to be an effect of the vagal part of the arterial baroreflex and did not necessary signal an impending vasovagal syncope. The present study indicates that although 10 days' HDT do not influence absolute BP responses to 70 degrees HUT BP was maintained by an increased sympathetic activity, reflected by an increased HR response and an augmented variance in BP around 0.1 Hz.
在6°头低位倾斜（HDT）10天后，通过被动70°头高位倾斜（HUT）评估模拟失重对直立性血压调节的影响。研究了6名健康男性志愿者。使用FinapresTM设备以非侵入性方式连续记录手指血压（BP）。瞬时心率（HR）由心电图得出。为了量化直立性血压变异性，对逐搏血压和RR间期值进行快速傅里叶变换（FFT）。10天HDT期后HUT前的对照心率增加，可能是由于受试对象的觉醒状态。与心率从24±2次/分钟增加到41±7次/分钟（P<0.05）相反，HUT引起的血压变化不受10天HDT的影响。HDT后直立性血压的总方差几乎增加了一倍。FFT表明，这种方差增加可归因于频率约为0.1Hz的血压振荡。在三名受试者中，观察到HDT后HUT期间的瞬时心率减速。对这些瞬态中血压与心率之间关系的分析表明，每次心率下降之前血压都会高于正常水平升高。因此，这些心率减速似乎是动脉压力感受器反射迷走神经部分的作用，并不一定预示即将发生血管迷走性晕厥。本研究表明，尽管10天的HDT不影响对70°HUT的绝对血压反应，但血压通过增加的交感神经活动得以维持，这表现为心率反应增加和0.1Hz左右的血压方差增大。
