Use of electrical impedance tomography (EIT) for the assessment of unilateral pulmonary function

Abstract

We describe a fully automatable quantification process for the assessment of unilateral pulmonary function (UPF) by means of EIT and propose a measurement protocol for its clinical implementation. Measurements were performed at the fourth and sixth intercostal levels on a first group of ten healthy subjects (5M, 5F, ages 26-48 years) to define the proper protocol by evaluating the most common postures and ventilation modes. Several off-line processing tools were also evaluated, including the use of digital filters to extract the respiratory components from EIT time series. Comparative measures were then carried out on a second group consisting of five preoperatory patients with lung cancer (4M, IF, ages 25-77 years) scheduled for radionuclide scanning. Results show that measurements were best performed with the subject sitting down, holding his arms up and breathing spontaneously. As regards data processing, it is best to extract Fourier respiratory components. The mean of the healthy subject group leads to a left-right division of lung ventilation consistent with literature values (47% left lung, 53% right lung). The comparative study indicates a good correlation (r = 0.96) between the two techniques, with a mean difference of (-0.4+/-5.4)%, suggesting that the elimination of cardiac components from the thoracic transimpedance signal leads to a better estimation of UPF.

Tidal volume monitoring by electrical impedance tomography (EIT) using different regions of interest (ROI): Calibration equations

“…This algorithm is aimed to optimize computing time. The software uses a weight matrix that takes into account the spatial sensitivity of each image's pixel [35]. Once about 30 s of tidal breathing are recorded and images are reconstructed, a signal that depicts the changes in impedance for every pixel in image over time is constructed.…”

Principles of electrical impedance tomography and its clinical application

“…Baisch (69) reported on experiences with EIT on board a space mission in 1993. The influence of gravity on regional lung function was also examined by EIT under different body positions on earth (70,71).…”

Tidal volume (TV) post-process obtained with electrical impedance tomography on a group of chronic obstructive pulmonary disease (COPD) patients. Use of adjust equations

“…It uses 16 electrodes and can obtain up to 17 frames/second. The electrodes (Red Dot 2560 -3M, London; Ontario, Canada) were placed around the thoracic box on the sixth intercostals space following the protocol described in [3]. This device was programmed to apply an electrical current of 1 mA RMS at 48 kHz.…”

“…On the other hand, there is another monitoring device based on the transmission of respiratory vibrations which is not yet tested enough for this application [2]. Suitability of Electrical Impedance Tomography (EIT) applied to ventilation measurement has been demonstrated for the Unilateral Pulmonary function (UPF) [3][4] and more recently for ventilatory pattern monitoring in healthy people [5]. The EIT procedure was validated for the estimation of tidal volume (TV) magnitudes in healthy people.…”