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EIT based intrathoracic pulsatile impedance measurements during apnea: a case study

EIT based intrathoracic pulsatile impedance measurements during apnea: a case study DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203014 Sabine Krueger-Ziolek*, András Lovas, Fatime Hawchar, Bernhard Laufer and Knut Moeller for the Digital Clones in Personalized Medicine (DCPM) study team EIT based intrathoracic pulsatile impedance measurements during apnea: a case study Abstract: Intrathoracic ventilation related and pulsatile Keywords: Electrical impedance tomography, pulsatile (perfusion) impedance changes can be measured by the non- impedance changes, apnea, blood gas analysis invasive and radiation-free imaging method Electrical https://doi.org/10.1515/cdbme-2020-3014 Impedance Tomography (EIT). Ventilation monitoring is still the key research area in EIT, whereby perfusion monitoring gain more and more in interest. However, there are still many 1 Introduction unknown influencing factors concerning pulsatile impedance measurements which have to be investigated. Hence, in this Respiratory failure is the third most common cause of death observational case study the impact of prolonged apnea worldwide clarifying the necessity of innovative methods of periods on pulsatile impedance changes was examined in a lung function monitoring. Electrical impedance tomography patient with suspected brain death undergoing several apnea (EIT), a still relatively unknown imaging technique, which is tests. In addition, the correlation between changes in pulsatile characterized by non-invasiveness, no radiation exposure, impedance and certain blood gas parameters (carbon dioxide bedside application and a high temporal resolution (up to 50 partial pressure, pCO ; oxygen partial pressure, pO ; pH; 2 2 - Hz), depicts such a novel lung function monitoring tool [1]. bicarbonate, HCO ) were explored. Results show that the In EIT, intrathoracic impedance changes, resulting from pulsatile impedance signal changes over time during apnea. air and blood volume variations, can be determined by An increase in the area under the curve (Mean AuC) and the circumferentially attaching surface electrodes on the thorax, maximum amplitude (Mean Max) of heart beat associated applying small alternating currents and measuring differences impedance signals was observed (Mean AuC: up to 65 %; in surface potentials. These potential differences are used to Mean Max: up to 57 %). Furthermore, a positive correlation - reconstruct impedance images which can be employed to between the increase in impedance and pCO and HCO was 2 3 assess ventilation and perfusion distribution [2]. assessed (both: up to 0.99), whereas pO and pH show a The main research area of EIT is ventilation monitoring negative correlation (both: up to -0.99). These preliminary during mechanical ventilation. However, since EIT is capable results indicate that pulsatile EIT monitoring may be applied of measuring ventilation based as well as cardiovascular to get additional information regarding cardio-pulmonary related (pulsatile) impedance changes, perfusion monitoring interactions sustaining diagnosis or treatment of lung comes more and more into research focus. Several previous diseases. studies introduced different ways of measuring and separating ventilation associated and pulsatile impedance ______ signals, for instance by injecting saline solution, applying *Corresponding author: Sabine Krueger-Ziolek: Institute of frequency filtering or principal component analysis [3]. Technical Medicine, Furtwangen University, Jakob-Kienzle-Straße Despite all this, the easiest way to measure pulsatile 17, Villingen-Schwenningen, Germany, krue@hs-furtwangen.de impedance changes is holding the breath, which is of course András Lovas, Fatime Hawchar: Department of Anaesthesiology not always feasible depending on the clinical situation (e.g. and Intensive Therapy, University of Szeged, Szeged, Hungary Bernhard Laufer, Knut Moeller: Institute of Technical Medicine, artificial respiration or spontaneous breathing). Furtwangen University, Villingen-Schwenningen, Germany In a previous study, we assessed changes in the pulsatile 1 2 DCPM study team: Balázs Benyó , Geoff Chase , Thomas impedance signal depending on lung volume during breath 3 4 Desaive , Knut Moeller 1 holding (approx. 10 seconds) in a spontaneously breathing Department of Control Engineering and Information, Budapest subject [4]. It was indicated that shape and amplitude of the University of Technology and Economics, Budapest, Hungary. Centre for Bioengineering, University of Canterbury, Christchurch, pulsatile impedance signal varied based on changes in lung New Zealand. volume. However, there are still a lot of unknown influencing GIGA Cardiovascular Science, University of Liege, Liege, Belgium. Open Access. © 2020 Sabine Krueger-Ziolek et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 1 Figure 1: Schematic illustration of the measurement procedure. Ventilation related and pulsatile impedance changes within the observational period (blue). Apnea test 1 to 3 (green) and concurrent blood gas analyses (BGA, red). factors which need to be explored. Thus, in this present case Hz to measure intrathoracic pulsatile impedance changes study, we evaluate changes in the pulsatile impedance signal (PulmoVista®500, Dräger Lübeck, Germany). Figure 1 in dependency on the duration of apnea and on variations in shows a schematic illustration of the measurement procedure. blood gas parameters in a mechanically ventilated patient with suspected brain death undergoing several apnea tests. 2.2 EIT Data processing The acquired EIT data were reconstructed into images of 2 Methods intrathoracic impedance changes (32 × 32 pixels) applying the manufacturer’s software (EIT Analysis Tool 6.3, Dräger, Germany) which employs a FEM-based linearized Newton- 2.1 Study protocol and data collection Raphson algorithm. Further calculations were conducted with MATLAB (R2017a, The Mathworks® Inc., Natick, USA). A female patient (51 years, 60 kg, 157 cm) with suspected To preclude image artefacts and impedance changes brain death was observed over a period of 12 hours from one based on other tissue than lung tissue as well as the and at the final apnea test from three independent doctors at ventricular region, a region of interest (ROI) was defined by the university hospital of Szeged (Hungary) to determine a using a linear regression fit [6]. Hence, linear regression was potential brain death. The patient suffered a subarachnoid applied between the signal of each pixel (regional signal) and haemorrhage, which is assigned to primary brain damages. the signal of the sum of all pixels (global signal). Afterwards, All three doctors exhibited the required licence to do this a functional EIT (fEIT) image was generated in which each examination and followed the standard procedure, which is pixel represents the slope of the individual linear regression strictly prescribed by the Hungarian law [5]. This standard fit. Pixels values of the fEIT image higher than 15 % of the procedure contains various required examinations, such as an maximum value of the fEIT image were included in the ROI. apnea test, which has to be repeated every 4 hours during the observation period. During these apnea tests, the patient was disconnected from the ventilator (after approx. 10 minutes of 1.0 FiO preoxygenation, pCO of 38-42 mmHg) and the doctors were looking for any respiratory movement as well as taking regularly arterial blood samples for blood gas analyses (every 2 to 3 minutes) until the patient reached a pCO level of 60 mmHg. According to the Hungarian law, the patient must be oxygenated during this time span, which was done by administering 6 L/min O into the endotracheal tube via a cannula. Figure 2: Schematic presentation of a mean impedance signal EIT measurements were conducted simultaneously at the th segment corresponding to one heart beat during apnea 5 intercostal space (8.4 mA, 93 kHz) with a frame rate of 50 (blue). Exemplarily, five individual impedance signal segments are shown (colored dashed lines). Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 1 2 and 3 HCO values showed a slightly ascending trend 2.3 EIT and blood gas analysis 3 - - (HCO3 : up to 6 %), whereas within apnea period 1 HCO3 values remained almost constant. Table 1 shows the accompanying correlation coefficients 2.3.1 EIT data analysis of the EIT based parameters (Mean AuC and Mean Max) and the corresponding average blood gas values (pH, pCO , pO The intrathoracic pulsatile EIT signal measured during an 2 2 and HCO ). apnea test was divided into signal sections of 2 to 3 minutes depending on the time points of the arterial blood sampling (Figure 1). Additionally, each EIT signal section was Table 1: Correlation coefficients of EIT (Mean AuC, Mean Max) separated into smaller signal segments corresponding to one and blood gas (pH, pCO , pO , BE, HCO ) parameters for all 2 2 3 three apnea periods. heart beat (Figure 2). A linear trend between the start and end point of each signal segment was removed as well as an interpolation of Mean AuC Mean Max each signal segment to the mean length of all signal segments Apnea 1 pH -0.9183 -0.9209 was conducted (refer to [4]). Subsequently, for each 2 to 3 pCO 0.8884 0.8912 minutes section, the mean signal of all signal segments was pO --- --- calculated (Figure 2). The area under the curve and the HCO -0.1037 -0.1007 maximum of the mean signal (Mean AuC and Mean Max) 3 were calculated for each interval, respectively. Apnea 2 pH -0.7582 -0.9775 pCO 0.7601 0.9743 pO -0.8426 -0.9833 2.3.2 Blood gas analysis HCO 0.7991 0.9651 During an apnea test, arterial blood samples were taken every Apnea 3 pH -0.9905 -0.9893 2 to 3 minutes to e.g. observe the carbon dioxide partial pCO 0.9916 0.9900 pressure (pCO ) concentration (refer to 2.1). However, pO -0.9971 -0.9983 several other blood components were determined such as pH, 2 oxygen partial pressure (pO ) or minerals like sodium (Na ). HCO 0.9939 0.9915 In this observational study the following analysis was restricted to pH, pCO2, pO2 and bicarbonate (HCO3 ). Since the mean EIT signal between two time points of 4 Discussion subsequent blood samplings was studied, the average of pH, pCO2, pO2 and HCO3 of the corresponding two time points were calculated. Additionally, the correlation between the Results of this observational case study demonstrate that the EIT based parameters (Mean AuC and Mean Max) and the EIT based parameters Mean AuC and Mean Max show a averaged blood gas parameters was examined. positive or negative correlation with certain blood gas parameters. During the apnea phases a clear increase in the area under the curve (Mean AuC) and the amplitude of the pulsatile impedance signal (Mean Max) was observed, which 3 Results was accompanied with a decline in pO and pH as well as with a rise in pCO . Figure 3 presents the Mean AuC and Mean Max values as Since the patient was disconnected from the ventilator well as the corresponding averaged pH, pCO , pO and 2 2 for several minutes and no gas exchange was taking place, O HCO values of all predefined time sections within the three was used up and CO was enriched within the body, which on apnea periods. An increase of Mean AuC, Mean Max and the other hand could result in respiratory acidosis (pH<7.35). pCO could be observed within all three apnea phases (Mean Furthermore, no gas exchange might have provoked to AuC: up to 65 %; Mean Max: up to 57 %; pCO : up to 24 %). less blood volume within the lung tissue which might have On the other hand, a decrease over the course of all apnea led to a decrease in conductivity, and thus to an increase in periods could be seen for pO and pH (pO : up to 9 %; pH: 2 2 impedance (implied by higher Mean AuC and Mean Max). up to 0.9 %). The averaged HCO values were inconsistent within the three different apnea periods. During apnea phases Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 2 Figure 3: EIT based measures (blue) and blood gas parameters (red) of the predefine time sections of all three apnea periods. HCO showed an inconsistent behaviour during the Acknowledgement three apnea tests. No removal of CO during apnea leads to This work was partially supported by the German Federal an accumulation of bicarbonate within the body, which Ministry of Education and Research (MOVE, Grant corroborates with the slightly increase in HCO3- in apnea 13FH628IX6) and has received funding from EU H2020 R&I period 2 and 3. During apnea period 1 HCO remained programme (MSCA-RISE-2019 call) under grant agreement almost the same which might be based on the flatter increase #872488 — DCPM. of pCO in comparison to apnea phase 2 and 3. However, these first results indicate that the pulsatile Author Statement EIT signal might change in amplitude and shape over time Conflict of interest: Authors state no conflict of interest. during apnea. Furthermore, results suggest that changes in Informed consent: Informed consent has been obtained from the pulsatile EIT signal correlate with certain blood gas all individuals included in this study. Ethical approval: The parameters, such as pO or pCO , which might provide research related to human use complies with all the relevant 2 2 additional information in EIT lung monitoring. national regulations, institutional policies and was performed Nevertheless, this observational case study represents in accordance with the tenets of the Helsinki Declaration, and only one patient. To confirm these observations, additional has been approved by the authors' institutional review board studies including more patients need to be undertaking. In or equivalent committee. addition, other influencing factors of pulsatile EIT monitoring, such as changes in cardiac activity (e.g. changes in heart beat volume), have to be considered and investigated. References [1] Gong B, Krueger-Ziolek S, Moeller K, Schullcke B, Zhao Z. Electrical impedance tomography: functional lung imaging on its way to clinical practice? Expert Rev Respir Med 2015; 9 5 Conclusion (6): 721-37. [2] Bodenstein M, David M, Markstaller K. Principles of electrical This observational case study shows that the pulsatile EIT impedance tomography and its clinical application. Crit Care Med 2009; 37 (2): 713-24. signal changes in height during a longer period of apnea. [3] Nguyen DT, Jin C, Thiagalingam A, McEwan AL. A review on Furthermore, it was observed that EIT pulsatile changes electrical impedance tomography for pulmonary perfusion correlate with blood gas parameters pCO , pO , pH and 2 2 imaging. Physiol Meas 2012; 33 (5): 695-706. HCO . Hence, pulsatile EIT monitoring might be used to 3 [4] Krueger-Ziolek S, Gong B, Laufer B, Moeller K. Impact of lung volume changes on perfusion estimates derived by gain further information concerning cardio-pulmonary Electrical Impedance Tomography. Current Directions in interactions supporting the diagnosis or treatment of lung Biomedical Engineering 2019; 5 (1): 199-202. diseases. [5] 1. melléklet a 12/2012. (VIII. 6.) EMMI rendelethez. Magyar Közlöny 2012;(105): 17688-89. [6] Frerichs I, Pulletz S, Elke G, Reifferscheid F, Schadler D, Scholz J, Weiler N. Assessment of changes in distribution of lung perfusion by electrical impedance tomography. Respiration 2009; 77 (3): 282-91. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Directions in Biomedical Engineering de Gruyter

EIT based intrathoracic pulsatile impedance measurements during apnea: a case study

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de Gruyter
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© 2020 by Walter de Gruyter Berlin/Boston
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2364-5504
DOI
10.1515/cdbme-2020-3014
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Abstract

DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203014 Sabine Krueger-Ziolek*, András Lovas, Fatime Hawchar, Bernhard Laufer and Knut Moeller for the Digital Clones in Personalized Medicine (DCPM) study team EIT based intrathoracic pulsatile impedance measurements during apnea: a case study Abstract: Intrathoracic ventilation related and pulsatile Keywords: Electrical impedance tomography, pulsatile (perfusion) impedance changes can be measured by the non- impedance changes, apnea, blood gas analysis invasive and radiation-free imaging method Electrical https://doi.org/10.1515/cdbme-2020-3014 Impedance Tomography (EIT). Ventilation monitoring is still the key research area in EIT, whereby perfusion monitoring gain more and more in interest. However, there are still many 1 Introduction unknown influencing factors concerning pulsatile impedance measurements which have to be investigated. Hence, in this Respiratory failure is the third most common cause of death observational case study the impact of prolonged apnea worldwide clarifying the necessity of innovative methods of periods on pulsatile impedance changes was examined in a lung function monitoring. Electrical impedance tomography patient with suspected brain death undergoing several apnea (EIT), a still relatively unknown imaging technique, which is tests. In addition, the correlation between changes in pulsatile characterized by non-invasiveness, no radiation exposure, impedance and certain blood gas parameters (carbon dioxide bedside application and a high temporal resolution (up to 50 partial pressure, pCO ; oxygen partial pressure, pO ; pH; 2 2 - Hz), depicts such a novel lung function monitoring tool [1]. bicarbonate, HCO ) were explored. Results show that the In EIT, intrathoracic impedance changes, resulting from pulsatile impedance signal changes over time during apnea. air and blood volume variations, can be determined by An increase in the area under the curve (Mean AuC) and the circumferentially attaching surface electrodes on the thorax, maximum amplitude (Mean Max) of heart beat associated applying small alternating currents and measuring differences impedance signals was observed (Mean AuC: up to 65 %; in surface potentials. These potential differences are used to Mean Max: up to 57 %). Furthermore, a positive correlation - reconstruct impedance images which can be employed to between the increase in impedance and pCO and HCO was 2 3 assess ventilation and perfusion distribution [2]. assessed (both: up to 0.99), whereas pO and pH show a The main research area of EIT is ventilation monitoring negative correlation (both: up to -0.99). These preliminary during mechanical ventilation. However, since EIT is capable results indicate that pulsatile EIT monitoring may be applied of measuring ventilation based as well as cardiovascular to get additional information regarding cardio-pulmonary related (pulsatile) impedance changes, perfusion monitoring interactions sustaining diagnosis or treatment of lung comes more and more into research focus. Several previous diseases. studies introduced different ways of measuring and separating ventilation associated and pulsatile impedance ______ signals, for instance by injecting saline solution, applying *Corresponding author: Sabine Krueger-Ziolek: Institute of frequency filtering or principal component analysis [3]. Technical Medicine, Furtwangen University, Jakob-Kienzle-Straße Despite all this, the easiest way to measure pulsatile 17, Villingen-Schwenningen, Germany, krue@hs-furtwangen.de impedance changes is holding the breath, which is of course András Lovas, Fatime Hawchar: Department of Anaesthesiology not always feasible depending on the clinical situation (e.g. and Intensive Therapy, University of Szeged, Szeged, Hungary Bernhard Laufer, Knut Moeller: Institute of Technical Medicine, artificial respiration or spontaneous breathing). Furtwangen University, Villingen-Schwenningen, Germany In a previous study, we assessed changes in the pulsatile 1 2 DCPM study team: Balázs Benyó , Geoff Chase , Thomas impedance signal depending on lung volume during breath 3 4 Desaive , Knut Moeller 1 holding (approx. 10 seconds) in a spontaneously breathing Department of Control Engineering and Information, Budapest subject [4]. It was indicated that shape and amplitude of the University of Technology and Economics, Budapest, Hungary. Centre for Bioengineering, University of Canterbury, Christchurch, pulsatile impedance signal varied based on changes in lung New Zealand. volume. However, there are still a lot of unknown influencing GIGA Cardiovascular Science, University of Liege, Liege, Belgium. Open Access. © 2020 Sabine Krueger-Ziolek et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 1 Figure 1: Schematic illustration of the measurement procedure. Ventilation related and pulsatile impedance changes within the observational period (blue). Apnea test 1 to 3 (green) and concurrent blood gas analyses (BGA, red). factors which need to be explored. Thus, in this present case Hz to measure intrathoracic pulsatile impedance changes study, we evaluate changes in the pulsatile impedance signal (PulmoVista®500, Dräger Lübeck, Germany). Figure 1 in dependency on the duration of apnea and on variations in shows a schematic illustration of the measurement procedure. blood gas parameters in a mechanically ventilated patient with suspected brain death undergoing several apnea tests. 2.2 EIT Data processing The acquired EIT data were reconstructed into images of 2 Methods intrathoracic impedance changes (32 × 32 pixels) applying the manufacturer’s software (EIT Analysis Tool 6.3, Dräger, Germany) which employs a FEM-based linearized Newton- 2.1 Study protocol and data collection Raphson algorithm. Further calculations were conducted with MATLAB (R2017a, The Mathworks® Inc., Natick, USA). A female patient (51 years, 60 kg, 157 cm) with suspected To preclude image artefacts and impedance changes brain death was observed over a period of 12 hours from one based on other tissue than lung tissue as well as the and at the final apnea test from three independent doctors at ventricular region, a region of interest (ROI) was defined by the university hospital of Szeged (Hungary) to determine a using a linear regression fit [6]. Hence, linear regression was potential brain death. The patient suffered a subarachnoid applied between the signal of each pixel (regional signal) and haemorrhage, which is assigned to primary brain damages. the signal of the sum of all pixels (global signal). Afterwards, All three doctors exhibited the required licence to do this a functional EIT (fEIT) image was generated in which each examination and followed the standard procedure, which is pixel represents the slope of the individual linear regression strictly prescribed by the Hungarian law [5]. This standard fit. Pixels values of the fEIT image higher than 15 % of the procedure contains various required examinations, such as an maximum value of the fEIT image were included in the ROI. apnea test, which has to be repeated every 4 hours during the observation period. During these apnea tests, the patient was disconnected from the ventilator (after approx. 10 minutes of 1.0 FiO preoxygenation, pCO of 38-42 mmHg) and the doctors were looking for any respiratory movement as well as taking regularly arterial blood samples for blood gas analyses (every 2 to 3 minutes) until the patient reached a pCO level of 60 mmHg. According to the Hungarian law, the patient must be oxygenated during this time span, which was done by administering 6 L/min O into the endotracheal tube via a cannula. Figure 2: Schematic presentation of a mean impedance signal EIT measurements were conducted simultaneously at the th segment corresponding to one heart beat during apnea 5 intercostal space (8.4 mA, 93 kHz) with a frame rate of 50 (blue). Exemplarily, five individual impedance signal segments are shown (colored dashed lines). Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 1 2 and 3 HCO values showed a slightly ascending trend 2.3 EIT and blood gas analysis 3 - - (HCO3 : up to 6 %), whereas within apnea period 1 HCO3 values remained almost constant. Table 1 shows the accompanying correlation coefficients 2.3.1 EIT data analysis of the EIT based parameters (Mean AuC and Mean Max) and the corresponding average blood gas values (pH, pCO , pO The intrathoracic pulsatile EIT signal measured during an 2 2 and HCO ). apnea test was divided into signal sections of 2 to 3 minutes depending on the time points of the arterial blood sampling (Figure 1). Additionally, each EIT signal section was Table 1: Correlation coefficients of EIT (Mean AuC, Mean Max) separated into smaller signal segments corresponding to one and blood gas (pH, pCO , pO , BE, HCO ) parameters for all 2 2 3 three apnea periods. heart beat (Figure 2). A linear trend between the start and end point of each signal segment was removed as well as an interpolation of Mean AuC Mean Max each signal segment to the mean length of all signal segments Apnea 1 pH -0.9183 -0.9209 was conducted (refer to [4]). Subsequently, for each 2 to 3 pCO 0.8884 0.8912 minutes section, the mean signal of all signal segments was pO --- --- calculated (Figure 2). The area under the curve and the HCO -0.1037 -0.1007 maximum of the mean signal (Mean AuC and Mean Max) 3 were calculated for each interval, respectively. Apnea 2 pH -0.7582 -0.9775 pCO 0.7601 0.9743 pO -0.8426 -0.9833 2.3.2 Blood gas analysis HCO 0.7991 0.9651 During an apnea test, arterial blood samples were taken every Apnea 3 pH -0.9905 -0.9893 2 to 3 minutes to e.g. observe the carbon dioxide partial pCO 0.9916 0.9900 pressure (pCO ) concentration (refer to 2.1). However, pO -0.9971 -0.9983 several other blood components were determined such as pH, 2 oxygen partial pressure (pO ) or minerals like sodium (Na ). HCO 0.9939 0.9915 In this observational study the following analysis was restricted to pH, pCO2, pO2 and bicarbonate (HCO3 ). Since the mean EIT signal between two time points of 4 Discussion subsequent blood samplings was studied, the average of pH, pCO2, pO2 and HCO3 of the corresponding two time points were calculated. Additionally, the correlation between the Results of this observational case study demonstrate that the EIT based parameters (Mean AuC and Mean Max) and the EIT based parameters Mean AuC and Mean Max show a averaged blood gas parameters was examined. positive or negative correlation with certain blood gas parameters. During the apnea phases a clear increase in the area under the curve (Mean AuC) and the amplitude of the pulsatile impedance signal (Mean Max) was observed, which 3 Results was accompanied with a decline in pO and pH as well as with a rise in pCO . Figure 3 presents the Mean AuC and Mean Max values as Since the patient was disconnected from the ventilator well as the corresponding averaged pH, pCO , pO and 2 2 for several minutes and no gas exchange was taking place, O HCO values of all predefined time sections within the three was used up and CO was enriched within the body, which on apnea periods. An increase of Mean AuC, Mean Max and the other hand could result in respiratory acidosis (pH<7.35). pCO could be observed within all three apnea phases (Mean Furthermore, no gas exchange might have provoked to AuC: up to 65 %; Mean Max: up to 57 %; pCO : up to 24 %). less blood volume within the lung tissue which might have On the other hand, a decrease over the course of all apnea led to a decrease in conductivity, and thus to an increase in periods could be seen for pO and pH (pO : up to 9 %; pH: 2 2 impedance (implied by higher Mean AuC and Mean Max). up to 0.9 %). The averaged HCO values were inconsistent within the three different apnea periods. During apnea phases Sabine Krueger-Ziolek et al., EIT based intrathoracic pulsatile impedance measurements during apnea: a case study — 2 Figure 3: EIT based measures (blue) and blood gas parameters (red) of the predefine time sections of all three apnea periods. HCO showed an inconsistent behaviour during the Acknowledgement three apnea tests. No removal of CO during apnea leads to This work was partially supported by the German Federal an accumulation of bicarbonate within the body, which Ministry of Education and Research (MOVE, Grant corroborates with the slightly increase in HCO3- in apnea 13FH628IX6) and has received funding from EU H2020 R&I period 2 and 3. During apnea period 1 HCO remained programme (MSCA-RISE-2019 call) under grant agreement almost the same which might be based on the flatter increase #872488 — DCPM. of pCO in comparison to apnea phase 2 and 3. However, these first results indicate that the pulsatile Author Statement EIT signal might change in amplitude and shape over time Conflict of interest: Authors state no conflict of interest. during apnea. Furthermore, results suggest that changes in Informed consent: Informed consent has been obtained from the pulsatile EIT signal correlate with certain blood gas all individuals included in this study. Ethical approval: The parameters, such as pO or pCO , which might provide research related to human use complies with all the relevant 2 2 additional information in EIT lung monitoring. national regulations, institutional policies and was performed Nevertheless, this observational case study represents in accordance with the tenets of the Helsinki Declaration, and only one patient. To confirm these observations, additional has been approved by the authors' institutional review board studies including more patients need to be undertaking. In or equivalent committee. addition, other influencing factors of pulsatile EIT monitoring, such as changes in cardiac activity (e.g. changes in heart beat volume), have to be considered and investigated. References [1] Gong B, Krueger-Ziolek S, Moeller K, Schullcke B, Zhao Z. Electrical impedance tomography: functional lung imaging on its way to clinical practice? Expert Rev Respir Med 2015; 9 5 Conclusion (6): 721-37. [2] Bodenstein M, David M, Markstaller K. Principles of electrical This observational case study shows that the pulsatile EIT impedance tomography and its clinical application. Crit Care Med 2009; 37 (2): 713-24. signal changes in height during a longer period of apnea. [3] Nguyen DT, Jin C, Thiagalingam A, McEwan AL. A review on Furthermore, it was observed that EIT pulsatile changes electrical impedance tomography for pulmonary perfusion correlate with blood gas parameters pCO , pO , pH and 2 2 imaging. Physiol Meas 2012; 33 (5): 695-706. HCO . Hence, pulsatile EIT monitoring might be used to 3 [4] Krueger-Ziolek S, Gong B, Laufer B, Moeller K. Impact of lung volume changes on perfusion estimates derived by gain further information concerning cardio-pulmonary Electrical Impedance Tomography. Current Directions in interactions supporting the diagnosis or treatment of lung Biomedical Engineering 2019; 5 (1): 199-202. diseases. [5] 1. melléklet a 12/2012. (VIII. 6.) EMMI rendelethez. Magyar Közlöny 2012;(105): 17688-89. [6] Frerichs I, Pulletz S, Elke G, Reifferscheid F, Schadler D, Scholz J, Weiler N. Assessment of changes in distribution of lung perfusion by electrical impedance tomography. Respiration 2009; 77 (3): 282-91.

Journal

Current Directions in Biomedical Engineeringde Gruyter

Published: Sep 1, 2020

Keywords: Electrical impedance tomography; pulsatile impedance changes; apnea; blood gas analysis

There are no references for this article.