Nebuya S, Noshiro M, Yonemoto A, Tateno S, Brown B H, Smallwood R H, Milnes P
Department of Clinical Engineering, Kitasato University, Sagamihara 228-8555, Japan.
Physiol Meas. 2006 May;27(5):S129-37. doi: 10.1088/0967-3334/27/5/S11. Epub 2006 Apr 20.
Inter-subject variability has caused the majority of previous electrical impedance tomography (EIT) techniques to focus on the derivation of relative or difference measures of in vivo tissue resistivity. Implicit in these techniques is the requirement for a reference or previously defined data set. This study assesses the accuracy and optimum electrode placement strategy for a recently developed method which estimates an absolute value of organ resistivity without recourse to a reference data set. Since this measurement of tissue resistivity is absolute, in Ohm metres, it should be possible to use EIT measurements for the objective diagnosis of lung diseases such as pulmonary oedema and emphysema. However, the stability and reproducibility of the method have not yet been investigated fully. To investigate these problems, this study used a Sheffield Mk3.5 system which was configured to operate with eight measurement electrodes. As a result of this study, the absolute resistivity measurement was found to be insensitive to the electrode level between 4 and 5 cm above the xiphoid process. The level of the electrode plane was varied between 2 cm and 7 cm above the xiphoid process. Absolute lung resistivity in 18 normal subjects (age 22.6 +/- 4.9, height 169.1 +/- 5.7 cm, weight 60.6 +/- 4.5 kg, body mass index 21.2 +/- 1.6: mean +/- standard deviation) was measured during both normal and deep breathing for 1 min. Three sets of measurements were made over a period of several days on each of nine of the normal male subjects. No significant differences in absolute lung resistivity were found, either during normal tidal breathing between the electrode levels of 4 and 5 cm (9.3 +/- 2.4 Omega m, 9.6 +/- 1.9 Omega m at 4 and 5 cm, respectively: mean +/- standard deviation) or during deep breathing between the electrode levels of 4 and 5 cm (10.9 +/- 2.9 Omega m and 11.1 +/- 2.3 Omega m, respectively: mean +/- standard deviation). However, the differences in absolute lung resistivity between normal and deep tidal breathing at the same electrode level are significant. No significant difference was found in the coefficient of variation between the electrode levels of 4 and 5 cm (9.5 +/- 3.6%, 8.5 +/- 3.2% at 4 and 5 cm, respectively: mean +/- standard deviation in individual subjects). Therefore, the electrode levels of 4 and 5 cm above the xiphoid process showed reasonable reliability in the measurement of absolute lung resistivity both among individuals and over time.
受试者间的变异性导致了大多数先前的电阻抗断层成像（EIT）技术专注于体内组织电阻率相对或差值测量的推导。这些技术隐含的要求是要有一个参考或先前定义的数据集。本研究评估了一种最近开发的方法的准确性和最佳电极放置策略，该方法无需参考数据集即可估计器官电阻率的绝对值。由于这种组织电阻率的测量是绝对的，单位为欧姆米，因此应该可以使用EIT测量来客观诊断诸如肺水肿和肺气肿等肺部疾病。然而，该方法的稳定性和可重复性尚未得到充分研究。为了研究这些问题，本研究使用了配置为使用八个测量电极运行的谢菲尔德Mk3.5系统。作为本研究的结果，发现绝对电阻率测量对剑突上方4至5厘米之间的电极水平不敏感。电极平面的水平在剑突上方2厘米至7厘米之间变化。在18名正常受试者（年龄22.6±4.9岁，身高169.1±5.7厘米，体重60.6±4.5千克，体重指数21.2±1.6：平均值±标准差）中，在正常呼吸和深呼吸1分钟期间测量了绝对肺电阻率。在几天的时间内，对9名正常男性受试者中的每一位进行了三组测量。发现在电极水平为4厘米和5厘米时的正常潮气呼吸期间（分别为9.3±2.4Ωm和9.6±1.9Ωm：平均值±标准差）或在电极水平为4厘米和5厘米时的深呼吸期间（分别为10.9±2.9Ωm和11.1±2.3Ωm：平均值±标准差），绝对肺电阻率没有显著差异。然而，在相同电极水平下正常潮气呼吸和深呼吸之间的绝对肺电阻率差异是显著的。在电极水平为4厘米和5厘米时的变异系数之间没有发现显著差异（分别为9.5±3.6%和8.5±3.2%：个体受试者的平均值±标准差）。因此，剑突上方4厘米和5厘米的电极水平在个体间和随时间测量绝对肺电阻率方面显示出合理的可靠性。
