Arbeille P, Sigaudo D, Pavy Le Traon A, Herault S, Porcher M, Gharib C
Unité de Médecine et Physiologie Spatiales, Faculté de Médecine, Centre Hospitalier Universitaire CHU Trousseau, Tours, France.
Eur J Appl Physiol Occup Physiol. 1998 Aug;78(3):208-18. doi: 10.1007/s004210050409.
The first objective of this study was to confirm that 4 days of head-down tilt (HDT) were sufficient to induce orthostatic intolerance, and to check if 4 days of physical confinement may also induce orthostatic intolerance. Evidence of orthostatic intolerance during tilt-up tests was obtained from blood pressure and clinical criteria. The second objective was to quantify the arterial and venous changes associated with orthostatic intolerance and to check whether abnormal responses to the tilt test and lower body negative pressure (LBNP) may occur in the absence of blood pressure or clinical signs of orthostatic intolerance. The cerebral and lower limb arterial blood flow and vascular resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during tilt-up and LBNP by ultrasound. Eight subjects were given 4 days of HDT and, 1 month later, 4 days of physical confinement. Tilt and LBNP test were performed pre- and post-HDT and confinement. Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%, P < 0.001). Cerebral haemodynamic responses to tilt-up and LBNP tests were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP tests the femoral vascular resistances increased less (P < 0.002), and the femoral blood flow reduced less (P < 0.001) after HDT than before HDT or after confinement. The cerebral to femoral blood flow ratio increased less after HDT than before (P < 0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed in the subjects who did not complete the tilt test. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (P < 0.01). In conclusion, 4 days of HDT were enough to alter the lower limb arterial vasoconstriction and venous distensibility during tilt-up and LBNP, which reduced the flow redistribution in favour of the brain in all HDT subjects. Confinement did not alter significantly the haemodynamic responses to orthostatic tests. The cerebral to femoral blood flow ratio measured during LBNP was the best predictor of orthostatic intolerance.
本研究的首要目标是确认4天的头低位倾斜（HDT）足以诱发直立不耐受，并检查4天的身体限制是否也会诱发直立不耐受。通过血压和临床标准获取倾斜试验期间直立不耐受的证据。第二个目标是量化与直立不耐受相关的动脉和静脉变化，并检查在没有血压或直立不耐受临床体征的情况下，倾斜试验和下体负压（LBNP）是否会出现异常反应。在倾斜试验和LBNP期间，通过超声评估脑和下肢动脉血流量、血管阻力、这两个区域之间的血流重新分布以及股静脉扩张情况。8名受试者接受了4天的HDT，1个月后又接受了4天的身体限制。在HDT和身体限制前后进行倾斜试验和LBNP试验。HDT后直立不耐受的发生率（63%）显著高于身体限制后（25%，P<0.001）。HDT前后或身体限制前后，脑血流动力学对倾斜试验和LBNP试验的反应相似。相反，在倾斜试验和LBNP试验期间，HDT后股血管阻力增加较少（P<0.002），股血流量减少较少（P<0.001），而HDT前或身体限制后则不然。HDT后脑与股血流量之比的增加幅度小于HDT前（P<0.002），但在身体限制前后保持不变。在未完成倾斜试验的受试者中，该比值受到的干扰明显更大。HDT后LBNP期间股浅静脉比HDT前或身体限制后更扩张（P<0.01）。总之，4天的HDT足以改变倾斜试验和LBNP期间下肢动脉血管收缩和静脉扩张能力，这减少了所有HDT受试者中有利于大脑的血流重新分布。身体限制并未显著改变对直立试验的血流动力学反应。LBNP期间测量的脑与股血流量之比是直立不耐受的最佳预测指标。
