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Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography

Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography Current Directions in Biomedical Engineering 2019;5(1):199-202 Sabine Krueger-Ziolek*, Bo Gong, Bernhard Laufer and Knut Moeller Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography Abstract: Electrical Impedance Tomography (EIT), an 1 Introduction imaging technique which operates non-invasively and without radiation exposure, provides information about Due to the continuously rising number of patients with ventilation- and cardiac-synchronous (pulsatile) changes in pulmonary diseases, the demand of new technologies for lung the lung. It is well known, that perfusion within the thorax is function monitoring increased. influenced by lung volume or intrathoracic pressure. In this Non-invasiveness, no radiation and a high temporal observational study, it shall be investigated if this resolution are just a few advantages characterizing Electrical phenomenon can be monitored by EIT. Therefore, the impact Impedance Tomography (EIT), a still relatively new of the amount of air within the lung on the pulsatile EIT functional imaging modality. Changes in impedance of the signal was evaluated by carrying out EIT measurements with lung tissue, induced by variations in air and blood volume a spontaneously breathing lung healthy subject holding the during respiration, can be reconstructed on the basis of breath at three different inspiratory and three various potentials measured at the surface of the thorax [1,2]. expiratory volume levels during normal tidal breathing. For Depending on the applied EIT system, surface potentials are EIT data analysis, a region of interest was defined by measured with 16 to 32 electrodes which are attached at the including lung tissue and excluding the heart region. The EIT thorax in the same distance to each other in a transversal data revealed, that the shape and the amplitude of the plane. For the measurements, the injection of a small pulsatile EIT signal (evaluated per heartbeat) during the alternating current (for example 5 mA, 50 kHz) is necessary, phases of breath holding were dependent on the enclosed which is harmless for the patient. The reconstructed lung volume. For lung volumes > 4 L, the amplitude of the impedance images can be used by clinicians to assess pulsatile EIT signal increased with rising inspiratory level changes in regional ventilation distribution within the lung. and the shape remained almost unchanged. For lung volumes So far, EIT is mainly employed for ventilation distribution < 4 L, a change in shape was visible but the amplitude monitoring in mechanically ventilated patients at the remained more or less the same with decreasing expiratory intensive care unit (ventilation therapy) [3,4], or for regional level. Since the results of this observational study show that lung function monitoring in spontaneously breathing patients the pulsatile EIT signal is influenced by the lung volume, it with obstructive lung diseases (diagnosis, follow-up and might be used in future to draw conclusions of cardiac- therapy response) [5-7]. pulmonary interactions or intrathoracic pressure states, Besides ventilation monitoring, EIT can be utilized to benefitting the treatment of intensive care patients. determine cardiac-synchronous (pulsatile) relative impedance Keywords: Electrical Impedance Tomography, perfusion, changes within the thorax. Impedance changes within the ventilation, pulmonary pressure, spontaneous breathing lung induced by blood volume changes can provide additional information on lung function (perfusion estimates), https://doi.org/10.1515/cdbme-2019-0051 benefitting treatment and therapy. Although, several EIT studies dealing with lung perfusion have already been conducted, there are still many unanswered questions in this ______ area of application. Most of the recent published studies were *Corresponding author: Sabine Krueger-Ziolek: Institute of animal experiments or addressed the application during Technical Medicine, Furtwangen University, Jakob-Kienzle-Straße mechanical ventilation [8,9]. 17, Villingen-Schwenningen, Germany, krue@hs-furtwangen.de However, this observational study was carried out during Bo Gong, Bernhard Laufer, Knut Moeller: Institute of Technical spontaneous breathing to investigate the impact of lung Medicine, Furtwangen University, Villingen-Schwenningen, Germany Open Access. © 2019 Sabine Krueger-Ziolek et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography — 200 Figure 1: Relative impedance changes measured during normal tidal breathing as well as during breath holding phases at various inspiratory and expiratory volume levels. volume on the pulsatile EIT signal. Since changes in lung 2.2 EIT data processing volume induce changes in pulmonary pressure, and thus A FEM based linearized Newton-Raphson algorithm was changes in perfusion, it was hypothesized that the pulsatile applied to reconstruct EIT images with a resolution of 32 × EIT signal may provide information on cardiac-pulmonary 32 pixels (EIT Analysis Tool 6.1, Dräger, Germany), interactions, which may support the treatment of intensive representing intrathoracic impedance changes. The following care patients. steps of the EIT data processing were implemented in MATLAB (R2017a, The Mathworks® Inc., Natick, USA). Since the body plethysmographic flow was measured with a 2 Methods sample rate of 200 Hz, the EIT data were interpolated to the same sample rate for further analysis. To confine the evaluation of the pulsatile impedance changes 2.1 Study protocol to the lung, a region of interest was defined by including lung tissue and excluding the heart region. Therefore, one EIT One lung healthy volunteer (male, 29 years, 184 cm, 77 kg) image at the highest inspiratory volume level (shortly before was performing normal tidal breathing in a body breath holding started) was selected and the maximum value plethysmograph (PowerCube®Body+, Ganshorn Medizin of this image was determined. 20% of this maximum value Electronic, Germany) and after approx. 7 tidal breaths, the was set as a threshold, meaning that all pixel values of the subject increased the inhaled breathing volume, held the selected image smaller than this threshold were not included breath at this inspiratory level for 10 to 12 seconds and to the lung region. The resulting lung contour was applied for returned to normal breathing afterwards. This scenario was all EIT images. done three times with various inspiratory volume levels. The heart region estimation was performed in the phase of Subsequently, this procedure was carried out with three breath holding at the lowest expiratory level. Since there is a different expiratory levels. th phase shift between impedance changes of the lung tissue and In parallel, EIT data were collected at the 5 intercostal space the heart region during one heartbeat (based on changes in (frame rate 50 Hz, 8 mA, 89 kHz) with a 16-electrode-system blood volume), it was possible to distinguish between lung (PulmoVista®500, Dräger, Germany) (Figure 1). tissue and the heart region. Pixels belonging to the heart For the sake of reproducibility, this measurement was region were specified during diastole to capture changes in executed two times as well as in reverse order, starting with heart position and size. The final ROI, which was applied to various expiratory volume levels followed by different all EIT images, was defined by subtracting the heart region inspiratory volume levels. from the lung contour. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomograph y— 201 Figure 2: Pulsatile EIT signal sections (thin, colored lines) determined during the phase of breath holding at three different inspiratory volume levels (IN-1: 5.03 L, IN-2: 5.55 L and IN-3: 6.66 L) and three various expiratory volume levels (EX- 1: 4.35 L, EX-2: 3.82 L and EX-3: 2.68 L) as well as the calculated mean signal (bold, red lines). increase in amplitude with rising lung volume is visible (EX- 2.3 Data analysis 1: 430, IN-1: 487, IN-2: 533 and IN-3: 550). A distinct The pulsatile EIT signal measured during the phase of breath change in the shape of the mean signal can be seen for holding was subdivided in signal sections corresponding to smaller lung volumes (< 4 L). Here, the amplitude remains the period of one heartbeat. A linear trend, obtained by the almost the same with decreasing expiratory level (EX-2: 341 linear fit based on the start point and end point of each signal and EX-3: 355), although the area under the curve decreases section, was removed from all signal sections respectively. (EX-2: 211, EX-3: 168). These observations (changes in Since the length of time of the signal sections slightly varied, shape and amplitude of the mean signal) could be made for the time span of each signal section has been rescaled to the all conducted measurements. mean time span of all signal sections. Afterwards, the mean signal of all sections was calculated (Figure 2). This procedure was applied for all the six phases of breath holding 4 Discussion (three inspiratory levels and three expiratory levels). The results of this observational study show that the enclosed air volume within the lung at breath holding influenced the 3 Results measured pulsatile EIT signal in shape and amplitude. So far, the results are not clearly interpretable. EIT reveals a relation Figure 2 exemplarily shows the individual pulsatile signal between lung volume and perfusion related signals. In sections as well as the mean signal of all sections of the three principle, it is assumed that the pulsatile signals show a larger various inspiratory levels (IN-1, IN-2 and IN-3) and of the amplitude with decreasing pressure and vice versa. During three different expiratory levels (EX-1, EX-2 and EX-3) of inspiration, a larger blood volume is reaching the heart one of the conducted measurements. (increase in preload) which might lead to the increase in Using the body plethysmograph, it was possible to assess the amplitude (IN-1, IN-2 and IN-3). In expiration, the opposite lung volume at the time of breath holding. The following happens which in turn may lead to the smaller amplitudes as lung volumes were determined at the various inspiratory and well as areas under the curve of the pulsatile signals (EX-1, expiratory volume levels: IN-1: 5.03 L, IN-2: 5.55 L, IN-3: EX-2 and EX-3). Other effects may be possible but further 6.66 L, EX-1: 4.35 L, EX-2: 3.82 L and EX-3: 2.68 L. speculations e.g. about muscle activities, elastic recoil or According to Figure 2, the shape of the mean signal remains cardiogenic oscillations during breath holding need to be almost the same for lung volumes > 4 L. In this case, an investigated in further experiments. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomograph y— 202 However, results of this preliminary study demonstrate that References the pulsatile EIT signal measured during breath holding is [1] Gong B, Krueger-Ziolek S, Moeller K, Schullcke B, Zhao Z. systematically affected by the size of lung volume implying Electrical impedance tomography: functional lung imaging on cardiac-pulmonary interactions. Multiple measurements and its way to clinical practice? Expert Rev Respir Med 2015; changing breathing order confirmed intra-subject 9(6):721-37. [2] Lundin S and Stenqvist O. Electrical impedance tomography: reproducibility of the results. Nonetheless, additional potentials and pitfalls. Curr Opin Crit Care 2012; 18(1):35-41. measurements with a higher number of subjects have to be [3] Costa EL, Borges JB, Melo A, Suarez-Sipmann F, Toufen C, undertaken to evaluate the inter-subject reproducibility of the Bohm SH, Amato MB. Bedside estimation of recruitable results. alveolar collapse and hyperdistension by electrical impedance tomography. Applied Physiology in Intensive Care Medicine 1: Springer 2012:165-170. [4] Karsten J, Grusnick C, Paarmann H, Heringlake M, Heinze 5 Conclusion H. Positive end‐expiratory pressure titration at bedside using electrical impedance tomography in post‐operative cardiac surgery patients. Acta Anaesthesiol Scand 2015; 59(6):723- This observational study shows that the shape and the 732. amplitude of the pulsatile EIT signal obtained during breath [5] Vogt B, Pulletz S, Elke G, Zhao Z, Zabel P, Weiler N, Frerichs I. Spatial and temporal heterogeneity of regional holding depend on the amount of air within the lung. It is lung ventilation determined by electrical impedance suspected that changes in the pulsatile signal were mainly tomography during pulmonary function testing. J Appl Physiol based on variations in pulmonary pressure inducing blood 2012; 113(7):1154-61. volume changes. Thus, EIT might be utilized in the future to [6] Frerichs I, Zhao Z, Becher T, Zabel P, Weiler N, Vogt B. non-invasively gain information about cardiac-pulmonary Regional lung function determined by electrical impedance interactions, benefitting clinical sectors like intensive care. tomography during bronchodilator reversibility testing in patients with asthma. Physiol Meas 2016; 37(6):698-712. [7] Krueger-Ziolek S, Schullcke B, Zhao Z, Gong B, Naehrig S, Acknowledgement Muller-Lisse U, Moeller K. Multi-layer ventilation inhomogeneity in cystic fibrosis. Respir Physiol Neurobiol 2016; 233:25-32. This work was partially supported by the German Federal [8] Borges JB, Suarez-Sipmann F, Bohm SH, Tusman G, Melo Ministry of Education and Research (MOVE, Grant A, Maripuu E, Sandstrom M, Park M, Costa EL, et al. 13FH628IX6). Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse. J Appl Physiol (1985) 2012; 112(1):225-36. Author Statement [9] Nguyen D, Bhaskaran A, Chik W, Barry M, Pouliopoulos J, Research funding: The author state no funding involved. Kosobrodov R, Jin C, Oh T, Thiagalingam A, et al. Perfusion Conflict of interest: Authors state no conflict of interest. redistribution after a pulmonary-embolism-like event with Informed consent: Informed consent has been obtained from contrast enhanced EIT. Physiol Meas 2015; 36(6):1297. all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors' institutional review board or equivalent committee. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Directions in Biomedical Engineering de Gruyter

Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography

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© 2019 by Walter de Gruyter Berlin/Boston
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Abstract

Current Directions in Biomedical Engineering 2019;5(1):199-202 Sabine Krueger-Ziolek*, Bo Gong, Bernhard Laufer and Knut Moeller Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography Abstract: Electrical Impedance Tomography (EIT), an 1 Introduction imaging technique which operates non-invasively and without radiation exposure, provides information about Due to the continuously rising number of patients with ventilation- and cardiac-synchronous (pulsatile) changes in pulmonary diseases, the demand of new technologies for lung the lung. It is well known, that perfusion within the thorax is function monitoring increased. influenced by lung volume or intrathoracic pressure. In this Non-invasiveness, no radiation and a high temporal observational study, it shall be investigated if this resolution are just a few advantages characterizing Electrical phenomenon can be monitored by EIT. Therefore, the impact Impedance Tomography (EIT), a still relatively new of the amount of air within the lung on the pulsatile EIT functional imaging modality. Changes in impedance of the signal was evaluated by carrying out EIT measurements with lung tissue, induced by variations in air and blood volume a spontaneously breathing lung healthy subject holding the during respiration, can be reconstructed on the basis of breath at three different inspiratory and three various potentials measured at the surface of the thorax [1,2]. expiratory volume levels during normal tidal breathing. For Depending on the applied EIT system, surface potentials are EIT data analysis, a region of interest was defined by measured with 16 to 32 electrodes which are attached at the including lung tissue and excluding the heart region. The EIT thorax in the same distance to each other in a transversal data revealed, that the shape and the amplitude of the plane. For the measurements, the injection of a small pulsatile EIT signal (evaluated per heartbeat) during the alternating current (for example 5 mA, 50 kHz) is necessary, phases of breath holding were dependent on the enclosed which is harmless for the patient. The reconstructed lung volume. For lung volumes > 4 L, the amplitude of the impedance images can be used by clinicians to assess pulsatile EIT signal increased with rising inspiratory level changes in regional ventilation distribution within the lung. and the shape remained almost unchanged. For lung volumes So far, EIT is mainly employed for ventilation distribution < 4 L, a change in shape was visible but the amplitude monitoring in mechanically ventilated patients at the remained more or less the same with decreasing expiratory intensive care unit (ventilation therapy) [3,4], or for regional level. Since the results of this observational study show that lung function monitoring in spontaneously breathing patients the pulsatile EIT signal is influenced by the lung volume, it with obstructive lung diseases (diagnosis, follow-up and might be used in future to draw conclusions of cardiac- therapy response) [5-7]. pulmonary interactions or intrathoracic pressure states, Besides ventilation monitoring, EIT can be utilized to benefitting the treatment of intensive care patients. determine cardiac-synchronous (pulsatile) relative impedance Keywords: Electrical Impedance Tomography, perfusion, changes within the thorax. Impedance changes within the ventilation, pulmonary pressure, spontaneous breathing lung induced by blood volume changes can provide additional information on lung function (perfusion estimates), https://doi.org/10.1515/cdbme-2019-0051 benefitting treatment and therapy. Although, several EIT studies dealing with lung perfusion have already been conducted, there are still many unanswered questions in this ______ area of application. Most of the recent published studies were *Corresponding author: Sabine Krueger-Ziolek: Institute of animal experiments or addressed the application during Technical Medicine, Furtwangen University, Jakob-Kienzle-Straße mechanical ventilation [8,9]. 17, Villingen-Schwenningen, Germany, krue@hs-furtwangen.de However, this observational study was carried out during Bo Gong, Bernhard Laufer, Knut Moeller: Institute of Technical spontaneous breathing to investigate the impact of lung Medicine, Furtwangen University, Villingen-Schwenningen, Germany Open Access. © 2019 Sabine Krueger-Ziolek et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography — 200 Figure 1: Relative impedance changes measured during normal tidal breathing as well as during breath holding phases at various inspiratory and expiratory volume levels. volume on the pulsatile EIT signal. Since changes in lung 2.2 EIT data processing volume induce changes in pulmonary pressure, and thus A FEM based linearized Newton-Raphson algorithm was changes in perfusion, it was hypothesized that the pulsatile applied to reconstruct EIT images with a resolution of 32 × EIT signal may provide information on cardiac-pulmonary 32 pixels (EIT Analysis Tool 6.1, Dräger, Germany), interactions, which may support the treatment of intensive representing intrathoracic impedance changes. The following care patients. steps of the EIT data processing were implemented in MATLAB (R2017a, The Mathworks® Inc., Natick, USA). Since the body plethysmographic flow was measured with a 2 Methods sample rate of 200 Hz, the EIT data were interpolated to the same sample rate for further analysis. To confine the evaluation of the pulsatile impedance changes 2.1 Study protocol to the lung, a region of interest was defined by including lung tissue and excluding the heart region. Therefore, one EIT One lung healthy volunteer (male, 29 years, 184 cm, 77 kg) image at the highest inspiratory volume level (shortly before was performing normal tidal breathing in a body breath holding started) was selected and the maximum value plethysmograph (PowerCube®Body+, Ganshorn Medizin of this image was determined. 20% of this maximum value Electronic, Germany) and after approx. 7 tidal breaths, the was set as a threshold, meaning that all pixel values of the subject increased the inhaled breathing volume, held the selected image smaller than this threshold were not included breath at this inspiratory level for 10 to 12 seconds and to the lung region. The resulting lung contour was applied for returned to normal breathing afterwards. This scenario was all EIT images. done three times with various inspiratory volume levels. The heart region estimation was performed in the phase of Subsequently, this procedure was carried out with three breath holding at the lowest expiratory level. Since there is a different expiratory levels. th phase shift between impedance changes of the lung tissue and In parallel, EIT data were collected at the 5 intercostal space the heart region during one heartbeat (based on changes in (frame rate 50 Hz, 8 mA, 89 kHz) with a 16-electrode-system blood volume), it was possible to distinguish between lung (PulmoVista®500, Dräger, Germany) (Figure 1). tissue and the heart region. Pixels belonging to the heart For the sake of reproducibility, this measurement was region were specified during diastole to capture changes in executed two times as well as in reverse order, starting with heart position and size. The final ROI, which was applied to various expiratory volume levels followed by different all EIT images, was defined by subtracting the heart region inspiratory volume levels. from the lung contour. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomograph y— 201 Figure 2: Pulsatile EIT signal sections (thin, colored lines) determined during the phase of breath holding at three different inspiratory volume levels (IN-1: 5.03 L, IN-2: 5.55 L and IN-3: 6.66 L) and three various expiratory volume levels (EX- 1: 4.35 L, EX-2: 3.82 L and EX-3: 2.68 L) as well as the calculated mean signal (bold, red lines). increase in amplitude with rising lung volume is visible (EX- 2.3 Data analysis 1: 430, IN-1: 487, IN-2: 533 and IN-3: 550). A distinct The pulsatile EIT signal measured during the phase of breath change in the shape of the mean signal can be seen for holding was subdivided in signal sections corresponding to smaller lung volumes (< 4 L). Here, the amplitude remains the period of one heartbeat. A linear trend, obtained by the almost the same with decreasing expiratory level (EX-2: 341 linear fit based on the start point and end point of each signal and EX-3: 355), although the area under the curve decreases section, was removed from all signal sections respectively. (EX-2: 211, EX-3: 168). These observations (changes in Since the length of time of the signal sections slightly varied, shape and amplitude of the mean signal) could be made for the time span of each signal section has been rescaled to the all conducted measurements. mean time span of all signal sections. Afterwards, the mean signal of all sections was calculated (Figure 2). This procedure was applied for all the six phases of breath holding 4 Discussion (three inspiratory levels and three expiratory levels). The results of this observational study show that the enclosed air volume within the lung at breath holding influenced the 3 Results measured pulsatile EIT signal in shape and amplitude. So far, the results are not clearly interpretable. EIT reveals a relation Figure 2 exemplarily shows the individual pulsatile signal between lung volume and perfusion related signals. In sections as well as the mean signal of all sections of the three principle, it is assumed that the pulsatile signals show a larger various inspiratory levels (IN-1, IN-2 and IN-3) and of the amplitude with decreasing pressure and vice versa. During three different expiratory levels (EX-1, EX-2 and EX-3) of inspiration, a larger blood volume is reaching the heart one of the conducted measurements. (increase in preload) which might lead to the increase in Using the body plethysmograph, it was possible to assess the amplitude (IN-1, IN-2 and IN-3). In expiration, the opposite lung volume at the time of breath holding. The following happens which in turn may lead to the smaller amplitudes as lung volumes were determined at the various inspiratory and well as areas under the curve of the pulsatile signals (EX-1, expiratory volume levels: IN-1: 5.03 L, IN-2: 5.55 L, IN-3: EX-2 and EX-3). Other effects may be possible but further 6.66 L, EX-1: 4.35 L, EX-2: 3.82 L and EX-3: 2.68 L. speculations e.g. about muscle activities, elastic recoil or According to Figure 2, the shape of the mean signal remains cardiogenic oscillations during breath holding need to be almost the same for lung volumes > 4 L. In this case, an investigated in further experiments. S. Krueger-Ziolek et al., Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomograph y— 202 However, results of this preliminary study demonstrate that References the pulsatile EIT signal measured during breath holding is [1] Gong B, Krueger-Ziolek S, Moeller K, Schullcke B, Zhao Z. systematically affected by the size of lung volume implying Electrical impedance tomography: functional lung imaging on cardiac-pulmonary interactions. Multiple measurements and its way to clinical practice? Expert Rev Respir Med 2015; changing breathing order confirmed intra-subject 9(6):721-37. [2] Lundin S and Stenqvist O. Electrical impedance tomography: reproducibility of the results. Nonetheless, additional potentials and pitfalls. Curr Opin Crit Care 2012; 18(1):35-41. measurements with a higher number of subjects have to be [3] Costa EL, Borges JB, Melo A, Suarez-Sipmann F, Toufen C, undertaken to evaluate the inter-subject reproducibility of the Bohm SH, Amato MB. Bedside estimation of recruitable results. alveolar collapse and hyperdistension by electrical impedance tomography. Applied Physiology in Intensive Care Medicine 1: Springer 2012:165-170. [4] Karsten J, Grusnick C, Paarmann H, Heringlake M, Heinze 5 Conclusion H. Positive end‐expiratory pressure titration at bedside using electrical impedance tomography in post‐operative cardiac surgery patients. Acta Anaesthesiol Scand 2015; 59(6):723- This observational study shows that the shape and the 732. amplitude of the pulsatile EIT signal obtained during breath [5] Vogt B, Pulletz S, Elke G, Zhao Z, Zabel P, Weiler N, Frerichs I. Spatial and temporal heterogeneity of regional holding depend on the amount of air within the lung. It is lung ventilation determined by electrical impedance suspected that changes in the pulsatile signal were mainly tomography during pulmonary function testing. J Appl Physiol based on variations in pulmonary pressure inducing blood 2012; 113(7):1154-61. volume changes. Thus, EIT might be utilized in the future to [6] Frerichs I, Zhao Z, Becher T, Zabel P, Weiler N, Vogt B. non-invasively gain information about cardiac-pulmonary Regional lung function determined by electrical impedance interactions, benefitting clinical sectors like intensive care. tomography during bronchodilator reversibility testing in patients with asthma. Physiol Meas 2016; 37(6):698-712. [7] Krueger-Ziolek S, Schullcke B, Zhao Z, Gong B, Naehrig S, Acknowledgement Muller-Lisse U, Moeller K. Multi-layer ventilation inhomogeneity in cystic fibrosis. Respir Physiol Neurobiol 2016; 233:25-32. This work was partially supported by the German Federal [8] Borges JB, Suarez-Sipmann F, Bohm SH, Tusman G, Melo Ministry of Education and Research (MOVE, Grant A, Maripuu E, Sandstrom M, Park M, Costa EL, et al. 13FH628IX6). Regional lung perfusion estimated by electrical impedance tomography in a piglet model of lung collapse. J Appl Physiol (1985) 2012; 112(1):225-36. Author Statement [9] Nguyen D, Bhaskaran A, Chik W, Barry M, Pouliopoulos J, Research funding: The author state no funding involved. Kosobrodov R, Jin C, Oh T, Thiagalingam A, et al. Perfusion Conflict of interest: Authors state no conflict of interest. redistribution after a pulmonary-embolism-like event with Informed consent: Informed consent has been obtained from contrast enhanced EIT. Physiol Meas 2015; 36(6):1297. all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors' institutional review board or equivalent committee.

Journal

Current Directions in Biomedical Engineering – de Gruyter

Published: Sep 1, 2019

Keywords: Electrical Impedance Tomography; perfusion; ventilation; pulmonary pressure; spontaneous breathing

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