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Electrical admittance for filling of the heart during lower body negative pressure in humans

2000; American Physiological Society; Volume: 89; Issue: 4 Linguagem: Inglês

10.1152/jappl.2000.89.4.1569

8750-7587

Yan Cai, Søren Holm, M. Jenstrup, M. Strømstad, Annika Eigtved, Jørgen Warberg, Liselotte Højgaard, Lars Friberg, Niels H. Secher,

Electrical and Bioimpedance Tomography

To evaluate whether electrical admittance of intracellular water is applicable for monitoring filling of the heart, we determined the difference in intracellular water in the thorax (Thorax ICW ), measured as the reciprocal value of the electrical impedance for the thorax at 1.5 and 100 kHz during lower body negative pressure (LBNP) in humans. Changes in Thorax ICW were compared with positron emission tomography-determined C 15 O-labeled erythrocytes over the heart. During −40 mmHg LBNP, the blood volume of the heart decreased by 21 ± 3% as the erythrocyte volume was reduced by 20 ± 2% and the plasma volume declined by 26 ± 2% ( P< 0.01; n = 8). Over the heart region, LBNP was also associated with a decrease in the technetium-labeled erythrocyte activity by 26 ± 4% and, conversely, an increase over the lower leg by 92 ± 5% ( P < 0.01; n = 6). For 15 subjects, LBNP increased thoracic impedance by 3.3 ± 0.3 Ω (1.5 kHz) and 3.0 ± 0.4 Ω (100 kHz), whereas leg impedance decreased by 9.0 ± 3.3 Ω (1.5 kHz) and 6.1 ± 3 Ω (100 kHz; P < 0.01). Thorax ICW was reduced by 7.1 ± 1.9 S · 10 −4 ( P < 0.01) and intracellular water in the leg tended to increase (from 37.8 ± 4.6 to 40.9 ± 5.0 S · 10 −4 ; P = 0.08). The correlation between Thorax ICW and heart erythrocyte volume was 0.84 ( P < 0.05). The results suggest that thoracic electrical admittance of intracellular water can be applied to evaluate changes in blood volume of the heart during LBNP in humans.