Bielefeld M R, Cabreriza S E, Spotnitz H M
Department of Surgery, Columbia University, College of Physicians and Surgeons, New York, NY 10032.
Ann Thorac Surg. 1993 Jun;55(6):1534-9. doi: 10.1016/0003-4975(93)91105-v.
The impedance catheter allows continuous measurement of ventricular volume. External influences have been described as causing parallel shifts in impedance-measured volumes; however, factors affecting impedance measurements in a nonparallel manner have not been fully characterized. Accordingly, an impedance catheter was placed inside a latex balloon into which known volumes of normal saline solution were injected. Conductive and nonconductive materials were individually placed within the balloon. Impedance was measured with materials touching (T) or not touching (NT) the catheter. Impedance-measured volumes were plotted versus actual volumes. Compared with the line of identity (LID), a statistical difference (p < 0.05) was found in the slopes in the presence of metallic objects only. These included a pacing lead (T, NT) (mT = 1.32m mNT = 1.29 versus mLID = 1.00), titanium (T) (mT = 1.68 versus mLID = 1.00), and aluminum (NT) (mNT = 0.72 versus mLID = 1.00). These changes in slope indicate nonparallel effects on impedance that confound the ability of the impedance catheter to determine volumes in vitro. These observations imply that serial calibration of both the slope constant (alpha) and the intercept (parallel conductance) of impedance may be necessary for in vivo measurements of ventricular volume based on impedance in the presence of metallic objects.
阻抗导管可连续测量心室容积。外部影响已被描述为会导致阻抗测量容积出现平行偏移；然而，以非平行方式影响阻抗测量的因素尚未得到充分表征。因此，将一根阻抗导管置于一个乳胶气球内，向其中注入已知体积的生理盐水溶液。将导电材料和非导电材料分别置于气球内。在材料接触（T）或不接触（NT）导管的情况下测量阻抗。将阻抗测量的容积与实际容积绘制成图。与恒等线（LID）相比，仅在存在金属物体时斜率存在统计学差异（p < 0.05）。这些金属物体包括一根起搏导线（T，NT）（mT = 1.32，mNT = 1.29，而mLID = 1.00）、钛（T）（mT = 1.68，而mLID = 1.00）和铝（NT）（mNT = 0.72，而mLID = 1.00）。斜率的这些变化表明对阻抗存在非平行影响，这会混淆阻抗导管在体外确定容积的能力。这些观察结果意味着，在存在金属物体的情况下，基于阻抗进行体内心室容积测量时，可能需要对阻抗的斜率常数（α）和截距（平行电导）进行连续校准。
