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# Three tests of the spirometry-EIT experiment.

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Article
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Electrical impedance tomography (EIT) provides global and regional information about ventilation by means of relative changes in electrical impedance measured with electrodes placed around the thorax. In combination with lung function tests, e.g. spirometry and body plethysmography, regional information about lung ventilation can be achieved. Imped...

## Contexts in source publication

Context 1
... study was designed as a self-study of the above mentioned authors. All of those lung-healthy subjects (1 female, 6 male, aged from 21 to 55 years) were asked to follow three breathing sequences illustrated in Figure 1. Each sequence consisted of an apnea, a synchronizing phase with spontaneous breathing and a test phase. ...
Context 2
... the test phase, subjects were asked to follow different tests. These tests are illustrated in Figure 1 and include different breathing patterns: ...
Context 3
... study was designed as a self-study of the above mentioned authors. All of those lung-healthy subjects (1 female, 6 male, aged from 21 to 55 years) were asked to follow three breathing sequences illustrated in Figure 1. Each sequence consisted of an apnea, a synchronizing phase with spontaneous breathing and a test ...
Context 4
... the apnea phase, subjects were asked to hold their breath after an inspiration for about 10 s, which was required for further time synchronization between the EIT and spirometry signal. During the synchronizing phase, subjects performed spontaneous breathing for five breaths. These measurements were used for the synchronisation of spirometry and EIT. In the test phase, subjects were asked to follow different tests. These tests are illustrated in Figure 1 and include different breathing ...

## Citations

... Electrical impedance tomography (EIT), as a noninvasive, nonradiological medical imaging method , can be used for bedside monitoring of the lung, both globally and regionally, even under dynamic lung ventilation. Lung impedance changes are highly correlated to the global volume changes measured at the airway opening (Ngo et al 2017, Zhao et al 2017. Recent clinical studies (Zhao et al 2019, Lumb et al 2020, Zhang et al 2020, Bayford et al 2022 imply the potential of EIT to assess the heterogeneous behavior of regional lung tissue from various conditions, including mask ventilation (Lumb et al 2020). ...
Article
Full-text available
... It has been shown that the impedance signal summed over the whole thoracic cross section correlates well with the inspired volume so long as the electrode plane is placed correctly [7]. A number of more sophisticated approaches have been applied that make use of the high frame rate to describe the breath-wise time dependence of aeration of different areas of the lung with exponential or polynomial fits. ...
... The results concerning spirometry (Tasks 1-3) are remarkable considering the fact that there are to-date no methods in the literature that are able to perform these tasks and generalize across patients. In fact, the only observable for which there is a contender for the presented approach is the linear sum model [7] for the reconstruction of volume from the EIT signal, which essentially applies a linear regression to the frame-wise sum of the EIT signal. However, the regression coefficients have to be adapted for each patient using a measurement of the actual tidal volume. ...
Article
Full-text available
Electrical impedance tomography (EIT) is a non-invasive imaging modality that allows a continuous assessment of changes in regional bioimpedance of different organs. One of its most common biomedical applications is monitoring regional ventilation distribution in critically ill patients treated in intensive care units. In this work, we put forward a proof-of-principle study that demonstrates how one can reconstruct synchronously measured respiratory or circulatory parameters from the EIT image sequence using a deep learning model trained in an end-to-end fashion. For this purpose, we devise an architecture with a convolutional feature extractor whose output is processed by a recurrent neural network. We demonstrate that one can accurately infer absolute volume, absolute flow, normalized airway pressure and within certain limitations even the normalized arterial blood pressure from the EIT signal alone, in a way that generalizes to unseen patients without prior calibration. As an outlook with direct clinical relevance, we furthermore demonstrate the feasibility of reconstructing the absolute transpulmonary pressure from a combination of EIT and absolute airway pressure, as a way to potentially replace the invasive measurement of esophageal pressure. With these results, we hope to stimulate further studies building on the framework put forward in this work.
... This study is in agreement with previous work showing a linear relationship in several species exists between VT EIT and VT Spiro using no PEEP [3,8,10] and indirectly PEEP [11,27,28]. Linearity was stable when breathing amplitude, extremes in lung volume and anthropometric characteristics varied [27,29]. However when PEEP was used to compare impedance change and volume change using nitrogen washout technique linearity was poor in critically ill patients [30]. ...
Article
Full-text available
Electrical impedance tomography (EIT) is used in lung physiology monitoring. There is evidence that EIT is linearly associated with global tidal volume (VT) in clinically healthy patients where no positive end-expiratory pressure (PEEP) is applied. This linearity has not been challenged by altering lung conditions. The aim of this study was to determine the effect of PEEP on VT estimation, using EIT technology and spirometry, and observe the stability of the relationship under changing lung conditions. Twelve male castrated cattle (Steer), mean age 7.8 months (SD ± 1.7) were premedicated with xylazine followed by anaesthesia induction with ketamine and maintenance with halothane in oxygen via an endotracheal tube. An EIT belt was applied around the thorax at the level of the fifth intercostal space. Volume controlled ventilation was used. PEEP was increased in a stepwise manner from 0 to 5, 10 and 15 cmH2O. At each PEEP, the VT was increased stepwise from 5 to 10 and 15 mL kg−1. After a minute of stabilisation, total impedance change (VTEIT), using EIT and VT measured by a spirometer connected to a flow-partitioning device (VTSpiro) was recorded for the following minute before changing ventilator settings. Data was analysed using linear regression and multi variable analysis. There was a linear relationship between VTEIT and VTSpiro at all levels of PEEP with an R2 of 0.71, 0.68, 0.63 and 0.63 at 0, 5, 10 and 15 cmH2O, respectively. The variance in VTEIT was best described by peak inspiratory pressure (PIP) and PEEP (adjusted R2 0.82) while variance in VTSpiro was best described by PIP and airway deadspace (adjusted R2 0.76). The relationship between VTEIT and VTSpiro remains linear with changes in tidal volume, and stable across altered lung conditions. This may have application for monitoring and assessment in vivo.
... Previous studies confirmed the excellent correlation of EIT with spirometry (Ngo et al 2017) and whole body plethysmography (Krueger-Ziolek et al 2015) under the conditions of tidal breathing and also during both types of full ventilation manoeuvres that were examined in our study. In contrast to the conventional pulmonary function testing methods, EIT enables the assessment of regional lung function. ...
Article
Objective: Current standards for conducting spirometry examinations recommend that the ventilation manoeuvres needed in pulmonary function testing are carried out repeatedly during the sessions. Chest electrical impedance tomography (EIT) can determine the presence of ventilation heterogeneity during such manoeuvres which increases the information content derived from such examinations. The aim of this study was to characterise regional lung function in patients with chronic obstructive pulmonary disease (COPD) during repetitive forced full ventilation manoeuvres. Regional lung function measures derived from these manoeuvres were compared with quiet tidal breathing. Approach: 60 hospitalised patients were examined during up to three repeated ventilation manoeuvres. 53 patients (12 women, 41 men; age: 68±17 years (mean±SD)) exhibited acceptable spirometry manoeuvres and EIT recordings suitable for analysis. Pixel values of tidal volume, forced full inspiratory and expiratory volume in 1s, forced inspiratory and expiratory vital capacity were calculated from the EIT data. Spatial ventilation heterogeneity was assessed using the coefficient of variation, global inhomogeneity index, centres and regional fractions of ventilation. Temporal inhomogeneity was examined by pixel expiration times needed to exhale 50% and 75% of regional forced vital capacity. Main results: All EIT-derived measures of regional lung function showed reproducible results during repetitive examinations. Parameters of spatial heterogeneity obtained from quiet tidal breathing were comparable with the measures derived from the forced manoeuvres. Significance: Measures of spatial and temporal ventilation heterogeneity obtained in COPD patients by EIT provide comparable findings during repeated examinations within one testing session. Quiet tidal breathing generates similar information on ventilation heterogeneity as forced manoeuvres that require high patient effort.
... Different numerical parameters have been found clinically useful, for example measures of variability along the left-right or ventral-dorsal axis (center of ventilation) and measures of ventilation inhomogeneity (global inhomogeneity index; coefficient of variation) [4]. It has been shown that the impedance signal summed over the whole thoracic cross section correlates well with the inspired volume [5]. A number of more sophisticated approaches have been applied that make use of the high frame rate to describe the breath-wise time dependence of aeration of different areas of the lung with exponential or polynomial fits. ...
... The results concerning spirometry (Tasks 1-3) are remarkable considering the fact that there are to-date no reliable methods in the literature that are able to perform these tasks and generalize across patients. In fact, the only observable for which there is a real contender for the presented approach is the linear sum model [5] for the reconstruction of volume from the EIT signal, which essentially applies a linear regression to the frame-wise sum of the EIT signal. However, the regression coefficients have to be adapted for each patient using a measurement of the actual tidal volume. ...
Preprint
Electrical impedance tomography (EIT) is a noninvasive imaging modality that allows a continuous assessment of changes in regional bioimpedance of different organs. One of its most common biomedical applications is monitoring regional ventilation distribution in critically ill patients treated in intensive care units. In this work, we put forward a proof-of-principle study that demonstrates how one can reconstruct synchronously measured respiratory or circulatory parameters from the EIT image sequence using a deep learning model trained in an end-to-end fashion. We demonstrate that one can accurately infer absolute volume, absolute flow, normalized airway pressure and within certain limitations even the normalized arterial blood pressure from the EIT signal alone, in a way that generalizes to unseen patients without prior calibration. As an outlook with direct clinical relevance, we furthermore demonstrate the feasibility of reconstructing the absolute transpulmonary pressure from a combination of EIT and absolute airway pressure, as a way to potentially replace the invasive measurement of esophageal pressure. With these results, we hope to stimulate further studies building on the framework put forward in this work.
... It is known that changes in tidal volume (VT) correlate well with changes in global EIT impedance [25,26]. Therefore, the ratio of EIT-derived VT versus true-ventilatorderived-VT should remain constant over time if no perturbation (such as EIT belt displacement or EIT electrode contact problem) occurred. ...
Article
Full-text available
Previous animal experiments have suggested that electrical impedance tomography (EIT) has the ability to noninvasively track changes in cardiac stroke volume (SV). The present study intended to reproduce these findings in patients during a fluid challenge. In a prospective observational study including critically ill patients on mechanical ventilation, SV was estimated via ECG-gated EIT before and after a fluid challenge and compared to transpulmonary thermodilution reference measurements. Relative changes in EIT-derived cardiosynchronous impedance changes in the heart ($$\Delta {\text{Z}}_{\text{H}}$$) and lung region ($$\Delta {\text{Z}}_{\text{L}}$$) were compared to changes in reference SV by assessing the concordance rate (CR) and Pearson’s correlation coefficient (R). We compared 39 measurements of 20 patients. $$\Delta {\text{Z}}_{\text{H}}$$ did not show to be a reliable estimate for tracking changes of SV (CR = 52.6% and R = 0.13 with P = 0.44). In contrast, $$\Delta {\text{Z}}_{\text{L}}$$ showed an acceptable trending performance (CR = 94.4% and R = 0.72 with P < 0.0001). Our results indicate that ECG-gated EIT measurements of $$\Delta {\text{Z}}_{\text{L}}$$ are able to noninvasively monitor changes in SV during a fluid challenge in critically ill patients. However, this was not possible using $$\Delta {\text{Z}}_{\text{H}}$$. The present approach is limited by the influences induced by ventilation, posture or changes in electrode–skin contact and requires further validation.
... To translate impedance images to volumes, a volume calibration is in place. A (linear) relation between impedance change and TV and/or vital capacity measured with spirometry is used to calibrate the images to volumes (64). Moreover, the fixed volume calibration can also be used to derive the relation between volume and image (65). ...
... The difference between spirometry and RIP is explained by Tobin et al. (74). They stated that the difference between both techniques is likely to result FIGURE 3 | Bias and limits of agreement distribution in liters for tidal volume (TV) (37,39,47,49,52,53,55,58,64,65,(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90), end-expiratory lung volume (EELV) (36,37,87,91), forced expiratory volume in 1s (FEV 1 ) (26,27,64,69,74,(92)(93)(94) and forced vital capacity (FVC) (69,74,92,93) per telemonitoring technique. Spiro; spirometry (including BbB-analyzers) in blue, RIP; respiratory inductance plethysmography in orange, RMP; respiratory magnetic plethysmography in gray, and EIT; electrical impedance tomography in yellow. ...
... The difference between spirometry and RIP is explained by Tobin et al. (74). They stated that the difference between both techniques is likely to result FIGURE 3 | Bias and limits of agreement distribution in liters for tidal volume (TV) (37,39,47,49,52,53,55,58,64,65,(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90), end-expiratory lung volume (EELV) (36,37,87,91), forced expiratory volume in 1s (FEV 1 ) (26,27,64,69,74,(92)(93)(94) and forced vital capacity (FVC) (69,74,92,93) per telemonitoring technique. Spiro; spirometry (including BbB-analyzers) in blue, RIP; respiratory inductance plethysmography in orange, RMP; respiratory magnetic plethysmography in gray, and EIT; electrical impedance tomography in yellow. ...
Article
Full-text available
Telemonitoring becomes more important in pulmonary research. It can be used to decrease the pressure on the health care system, to lower the costs of health care and to increase quality of life of patients. Previous studies show contradictory results regarding the effectiveness of telemonitoring. According to multiple researchers, inefficiency can be a result of poor study design, low data quality and usability issues. To counteract these issues, this review proves for an in-depth explanation of four (potential) telemonitoring systems in terms of work principle, accuracy, disturbing factors and usability. The evaluated systems are portable spirometry/breath-by-breath analyzers, respiratory inductance and magnetic plethysmography and electrical impedance tomography. These insights can be used to select the optimal technique for a specific purpose in future studies.
... The resultant voltages are measured and, subsequently, relative impedance changes are reconstructed in the measurement plane. Impedance changes are highly correlated to the global volume changes measured at the airway opening , Ngo et al 2017. ...
Article
Objective: The aim of the study was to examine whether electrode belt of electrical impedance tomography (EIT) changed lung function in healthy volunteers, patients with respiratory muscle weakness (RMW) and chronic obstructive pulmonary disease (COPD). Approach: In total 30 subjects were included (10 healthy volunteers, 10 subjects with RMW, maximum inspiratory pressure < 40 cmH2O, and 10 COPD, grade I - IV). Spirometry measurements were conducted in sitting position once a day at similar times on two consecutive days. Slow expiratory vital capacity (VC), forced vital capacity (FVC) and maximum voluntary ventilation (MVV) manoeuvres were performed. On day 1, spirometry was performed without the EIT electrode belt, and on day 2 the belt attached to the thorax. Main results: Lung function was not influenced by the electrode belt in healthy subjects. Test-retest reliability in the healthy group was 0.89, 0.89 and 0.85 for VC, FVC and MVV, respectively. On the other hand, all investigated parameters were significantly decreased in the RMW group (VC, 51.3±18.0 vs. 46.5±18.0 %predicted, without vs. with EIT belt, p<0.01; FVC, 51.7±19.0 vs. 45.8±18.1 %predicted, p<0.01; MVV, 41.0±20.0 vs. 38.8±19.6 %predicted, p<0.01). VC and MVV also decreased significantly in the COPD group (VC, 77.4±20.5 vs. 74.6±18.8 %predicted, p<0.05; MVV, 57.4±15.7 vs. 54.4±12.5 %predicted, p<0.05). Significance: EIT electrode belt could reduce lung volumes in subjects with pre-existing lung diseases. Comparing lung function acquired with electrode belt to corresponding values obtained without the belt should be avoided.
... The EIT impedance changes correlate strictly with spirometric data during the forced expiration manoeuvre [35]. Therefore, EIT can be used as a diagnostic tool providing the information about the regional pulmonary function in addition to the global one determined by conventional PFT. ...
Article
Full-text available
Electrical impedance tomography (EIT) is able to detect rapid lung volume changes during breathing. The aim of our observational study was to characterise the heterogeneity of regional ventilation distribution in lung-healthy adults by EIT and to detect the possible impact of tobacco consumption. A total of 219 nonsmokers, asymptomatic ex-smokers and current smokers were examined during forced full expiration using EIT. Forced expiratory volume in 1 s (FEV 1 ), forced vital capacity (FVC) and FEV 1 /FVC were determined in 836 EIT image pixels for the analysis of spatial and temporal ventilation distribution. Coefficients of variation (CVs) of these pixel values were calculated. Histograms and medians of FEV 1 /FVC EIT and times required to exhale 50%, 75%, 90% of FVC EIT (t 50 , t 75 and t 90 ) were generated. CV of FEV 1 /FVC EIT distinguished among all groups (mean± sd : nonsmokers 0.43±0.05, ex-smokers 0.52±0.09, smokers 0.62±0.16). Histograms of FEV 1 /FVC EIT differentiated between nonsmokers and the other groups (p<0.0001). Medians of t 50 , t 75 and t 90 showed the lowest values in nonsmokers. Median t 90 separated all groups (median (interquartile range): nonsmokers 0.82 (0.67–1.15), ex-smokers 1.41 (1.03–2.21), smokers 1.91 (1.33–3.53)). EIT detects regional ventilation heterogeneity during forced expiration in healthy nonsmokers and its increase in asymptomatic former and current smokers. Therefore, EIT-derived reference values should only be collected from nonsmoking lung-healthy adults.
... The validity and reproducibility of electrical impedance tomography for assessing distribution of ventilation has compared favorably with other lung imaging and diagnostic techniques, such as computed tomography, positron emission tomography, and pulmonary function tests that are used to measure FRC. [8][9][10][11] This technique can provide quantifiable data that will help us to determine the effectiveness of lung expansion therapy in our subject population. ...
Article
Background: Lung expansion therapy is often ordered after surgery to improve alveolar ventilation and reduce risks of postoperative pulmonary complications. The impact of lung expansion therapy at altering ventilation in patients who are not intubated has not been described. The primary purpose of this study was to determine if there is a difference in dorsal redistribution of ventilation and incidences of postoperative pulmonary complications when comparing incentive spirometry (IS) with EzPAP lung expansion therapy after upper abdominal surgery. Our a priori null hypothesis was that there are no differences. Methods: This randomized controlled trial enrolled adult human subjects after upper- abdominal surgery from January 2017 to November 2018. The subjects were allocated to receive IS or EzPAP 3 times a day on postoperative days 1-5. An electrical impedance tomography device was connected to the subjects for a single lung expansion therapy session on postoperative days 1, 3, and 5 to measure the change in post-lung expansion therapy dorsal end-expiratory lung impedance (ΔEELI%). Lung expansion therapy sessions with electrical impedance tomography included 2 min of normal breathing, 3 cycles of 10 breaths, and 2 min of normal breathing after cycle 3. Postoperative pulmonary complications were screened until hospital discharge. Mann-Whitney, chi-square, and Fisher exact tests were applied. Data were reported as count (n), percentage, and median (interquartile range) for primary and secondary outcomes. Alpha (2-tailed) was < 0.05. Results: A total of 112 subjects were enrolled to receive IS (n = 56) or EzPAP (n = 56). Baseline characteristics were equal. Post-lung expansion therapy dorsal ΔEELI% increased for both groups, but the dorsal ΔEELI% for IS versus EzPAP on postoperative day 1 (16% versus 12%, P = .39), postoperative day 3 (6% versus 6%, P = .68), and postoperative day 5 (9% versus 6%, P = .46) was not significantly different. Hospital length of stay (4 d; P = .30) and incidence of postoperative pulmonary complications (3.6% versus 7.1%, P = .19) were similar. Conclusions: There was no significant post-lung expansion therapy dorsal ΔEELI% or postoperative pulmonary complications among the adults who received IS or EzPAP 3 times a day after upper abdominal surgery. (ClinicalTrials.gov registration NCT02892773.).