Sageman W S
Department of Internal Medicine-Pulmonary Division, Naval Medical Center San Diego, CA 92134-5000, USA.
Crit Care Med. 1999 Sep;27(9):1986-90. doi: 10.1097/00003246-199909000-00044.
To evaluate the reliability and precision of measurement in a new thoracic electrical bioimpedance (TEB) monitor.
Prospective clinical trial using healthy volunteers.
Military tertiary care teaching hospital.
Seventy-five healthy adult volunteers taking no medications.
Induction of severe preload reduction using a standardized lower-body negative pressure protocol. Measurement of hemodynamic variables using a TEB monitor before, during, and immediately after application of negative pressure.
Seventy-five subjects were enrolled and completed the study. Pulse, blood pressure, stroke index, cardiac index, systolic time ratios (STR), and index of contractility were obtained on all subjects undergoing monitoring with the lower body negative pressure (LBNP) device. Hemodynamic measurements were recorded at 15-sec intervals during incremental application of 0, -10, -20, -40, and -60 mm Hg pressure for 10 mins at each pressure. Maximal tolerated LBNP produced reductions in cardiac, stroke, and contractility indices of 50%, 65%, and 45%, respectively. Pulse and STRs increased 44% and 113%, respectively. The precision of measurement (mean +/- 2 SD) for TEB-derived cardiac and stroke index was 16% and 10%, respectively. Repeatability of measurement was assessed by measuring hemodynamic changes after the abrupt cessation of maximal LBNP. There were significant increases in stroke index (p < .001) and decreases in STRs (p < .001) and pulse (p < .001) 3 mins after LBNP. There was no significant difference between initial and post-LBNP cardiac index (p > .05). Regression equations were applied to scattergram plots of stroke index vs. STRs and index of contractility vs. body mass. The use of these plots allowed elimination of values that appeared to be spurious (stroke index vs. STRs) and also raised the question whether the Sramek-Bemstein equation (stroke volume = left ventricular ejection time x volume of electrically participating tissue x dZ/dt/Zo) fully explained all the factors affecting the TEB waveform.
This new monitor appears to overcome many of the signal processing problems encountered with previous devices. The results clearly demonstrate that accurate and reliable measurement of bioimpedance waveforms is possible and suggest that the monitor is capable of generating precise hemodynamic data across a wide spectrum of hemodynamic alterations. However, the evidence also indicates that new algorithms may be needed to more fully explain the multiple factors affecting this waveform.
评估一种新型胸段电阻抗（TEB）监测仪测量的可靠性和精确性。
使用健康志愿者的前瞻性临床试验。
军队三级护理教学医院。
75名未服用药物的健康成年志愿者。
采用标准化的下体负压方案诱导严重的前负荷降低。在施加负压前、施加过程中及施加后立即使用TEB监测仪测量血流动力学变量。
75名受试者入选并完成研究。对所有使用下体负压（LBNP）装置进行监测的受试者测量脉搏、血压、每搏指数、心脏指数、收缩期时间比（STR）和收缩性指数。在每次压力下，以0、-10、-20、-40和-60 mmHg压力递增施加10分钟期间，每隔15秒记录一次血流动力学测量值。最大耐受LBNP分别使心脏、每搏和收缩性指数降低50%、65%和45%。脉搏和STR分别增加44%和113%。TEB衍生的心脏和每搏指数测量的精确性（均值±2标准差）分别为16%和10%。通过在最大LBNP突然停止后测量血流动力学变化来评估测量的重复性。LBNP后3分钟，每搏指数显著增加（p < 0.001），STR和脉搏显著降低（p < 0.001）。LBNP前后心脏指数无显著差异（p > 0.05）。将回归方程应用于每搏指数与STR以及收缩性指数与体重的散点图。使用这些图可以排除看似虚假的值（每搏指数与STR），同时也提出了Sramek-Bemstein方程（每搏量 = 左心室射血时间×电参与组织体积×dZ/dt/Zo）是否能完全解释影响TEB波形的所有因素的问题。
这种新型监测仪似乎克服了先前设备遇到的许多信号处理问题。结果清楚地表明，生物阻抗波形的准确可靠测量是可能实现的，这表明该监测仪能够在广泛的血流动力学改变范围内生成精确的血流动力学数据。然而，证据也表明可能需要新的算法来更全面地解释影响该波形的多种因素。
