Cai Y, Boesen M, Strømstad M, Secher N H
Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Denmark.
Eur J Appl Physiol. 2000 Nov;83(4 -5):356-62. doi: 10.1007/s004210000296.
During 50 degrees head-up tilt (HUT), the number of erythrocytes within the thorax has been shown to be reduced by approximately 25% and this level is retained during a maintained tilt, whilst that in the thigh increases by approximately 70%. To evaluate whether the electrical admittance of intracellular water (ICW) may be used to monitor this redistribution of red cells in humans, we determined the regional difference in the reciprocal value of the impedance at 1.5 and 100 kHz for the thorax (thoraxICW) and for the leg (legICW). In ten subjects all variables remained unchanged during head-down tilt but during HUT, presyncopal symptoms were induced in eight subjects after a mean of 27 (SEM 7) min as mean heart rate dropped from 85 (SEM 4) to 66 (SEM 3) beats x min(-1), mean arterial blood pressure from 80 (SEM 3) to 60 (SEM 5) mmHg, and mean oxygen saturation of venous blood from 76 (SEM 2)% to 73 (SEM 3)% (P < 0.05). The mean haematocrit increased from 50 (SEM 5)% to 52.5 (SEM 3.5)% (P < 0.01) and mean central venous pressure decreased during tilting (from a mean of 1 (SEM 1) to a mean of -1 (SEM 1) mmHg; P < 0.05) and returned to value at rest during the maintained tilt. Mean thoracic impedances increased by 7.0 (SEM 1.0) ohms (1.5 kHz) and 5.4 (SEM 1.2) ohms (100 kHz), and mean leg impedances decreased by 9.3 (SEM 1.2) ohms (1.5 kHz) and 3.1 (SEM 1.0) ohms (100 kHz) (P < 0.01). Mean thoraxICW decreased at 40 degrees HUT and remained reduced by 11 (SEM 2) S x 10(-4) (P < 0.05) until the presyncopal symptoms developed, at which time it was lower by 16 (SEM 2) S x 10(-4) (P < 0.01). Mean legICW increased from 97 (SEM 15) to 99 (SEM 15) S x 10(-4) (P = 0.08) during HUT but decreased during maintained tilt (to 94 (SEM 15) S x 10(-4); P < 0.05). The results suggested that during HUT, the difference in electrical admittance at a high and a low frequency current reflects the reduced number of red cells within the thorax.
在50度头高位倾斜（HUT）期间，已表明胸腔内的红细胞数量减少了约25%，并且在持续倾斜期间这一水平保持不变，而大腿中的红细胞数量增加了约70%。为了评估细胞内水（ICW）的电阻抗是否可用于监测人体红细胞的这种重新分布，我们测定了胸部（thoraxICW）和腿部（legICW）在1.5 kHz和100 kHz时阻抗倒数的区域差异。在10名受试者中，头低位倾斜期间所有变量均保持不变，但在HUT期间，平均心率从85（标准误4）次/分钟降至66（标准误3）次/分钟，平均动脉血压从80（标准误3）mmHg降至60（标准误5）mmHg，静脉血平均氧饱和度从76（标准误2）%降至73（标准误3）%（P<0.05），8名受试者在平均27（标准误7）分钟后出现前驱晕厥症状。平均血细胞比容从50（标准误5）%增加到52.5（标准误3.5）%（P<0.01），倾斜期间平均中心静脉压降低（从平均1（标准误1）mmHg降至平均 -1（标准误1）mmHg；P<0.05），并在持续倾斜期间恢复到静息值。平均胸部阻抗在1.5 kHz时增加了7.0（标准误1.0）欧姆，在100 kHz时增加了5.4（标准误1.2）欧姆，平均腿部阻抗在1.5 kHz时降低了9.3（标准误1.2）欧姆，在100 kHz时降低了3.1（标准误1.0）欧姆（P<0.01）。在40度HUT时，平均thoraxICW降低，并在出现前驱晕厥症状之前一直降低11（标准误2）S×10⁻⁴（P<0.05），此时其降低了16（标准误2）S×10⁻⁴（P<0.01）。在HUT期间，平均legICW从97（标准误15）增加到99（标准误15）S×10⁻⁴（P = 0.08），但在持续倾斜期间降低（至94（标准误15）S×10⁻⁴；P<0.05）。结果表明，在HUT期间，高频和低频电流下电阻抗的差异反映了胸腔内红细胞数量的减少。
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