Brown Clive M, Dütsch Matthias, Hecht Martin J, Neundörfer Bernhard, Hilz Max J
Autonomic Laboratory, Department of Neurology, University of Erlangen-Nuremberg, Schwabachanlage 6, Germany.
J Neurol Sci. 2003 Apr 15;208(1-2):71-8. doi: 10.1016/s0022-510x(02)00438-0.
The aim of this study was to determine whether lower body negative pressure (LBNP), combined with noninvasive methods of assessing changes in systemic and cerebral vascular resistance, is suitable as a method for assessing cerebral autoregulation. In 13 subjects we continuously assessed heart rate, blood pressure, cerebral blood flow velocity (CBFV) and cardiac output during graded levels of LBNP from 0 to -50 mm Hg. With increasing levels of LBNP, cardiac output declined significantly (to 55.8+/-4.5% of baseline value) but there was no overall change in mean arterial pressure. CBFV also fell at higher levels of LBNP (to 81.4+/-3.2% of baseline) but the percentage CBFV change was significantly less than that in cardiac output (P<0.01). The maximum increase in cerebrovascular resistance (pulsatility ratio) was significantly less than that in total peripheral resistance (17+/-6% vs. 105+/-16%, P<0.01). Spectral analysis showed that the power of low-frequency oscillations in mean arterial pressure, but not CBFV, increased significantly at the -50 mm Hg level of LBNP. These results show that, even during high levels of orthostatic stress, cerebral autoregulation is preserved and continues to protect the cerebral circulation from changes in the systemic circulation. Furthermore, assessment of cardiovascular and cerebrovascular parameters during LBNP may provide a useful clinical test of cerebral autoregulation.
本研究的目的是确定下体负压（LBNP）结合评估全身和脑血管阻力变化的非侵入性方法，是否适合作为评估脑自动调节的一种方法。在13名受试者中，我们在LBNP从0至-50 mmHg分级水平期间持续评估心率、血压、脑血流速度（CBFV）和心输出量。随着LBNP水平的升高，心输出量显著下降（降至基线值的55.8±4.5%），但平均动脉压无总体变化。在较高的LBNP水平时CBFV也下降（降至基线的81.4±3.2%），但CBFV的变化百分比显著小于心输出量的变化百分比（P<0.01）。脑血管阻力（搏动指数）的最大增加显著小于总外周阻力的增加（17±6%对105±16%，P<0.01）。频谱分析表明，在LBNP为-50 mmHg水平时，平均动脉压而非CBFV的低频振荡功率显著增加。这些结果表明，即使在高水平的直立位应激期间，脑自动调节仍得以保留，并继续保护脑循环免受体循环变化的影响。此外，在LBNP期间评估心血管和脑血管参数可能为脑自动调节提供一种有用的临床测试。
