Impedance Research Articles

Distribution of airway pressure opening in the lungs measured with electrical impedance tomography (POET): a prospective physiological study

Abstract Background In patients with acute hypoxemic respiratory failure (AHRF) under mechanical ventilation, the change in pressure slope during a low-flow insufflation indicates a global airway opening pressure (AOP) needed to reopen closed airways and may be used for titration of positive end-expiratory pressure. Objectives To understand 1) if airways open homogeneously inside the lungs or significant regional AOP variations exist; 2) whether the pattern of the pressure slope change during low-flow insufflation can indicate the presence of regional AOP variations. Methods Using electrical impedance tomography, we recorded low-flow insufflation maneuvers (< 10 L/min) starting from end-expiratory positive pressure 0–5 cmH2O. We measured global (AOPglobal) and regional AOPs from pressure-impedance curves in the four different lung quadrants, and compared AOPglobal with the highest quadrantal AOP (AOPhighest). We categorized the slope change of the low-flow inflation pressure–time curve into three patterns: no change, progressive change, abrupt change. Results Among the 36 patients analyzed, 9 (25%) had AOPglobal ≥ 5 cmH2O whereas 19 (53%) exhibited regional AOPhighest ≥ 5 cmH2O. AOPglobal was on average similar to AOP of the upper right quadrant (P = 0.182) but was lower than AOPs of the other three quadrants (P < 0.01 of each). AOPglobal was significantly lower than AOPhighest: 3.0 [2.0–4.3] vs. 5.0 [2.8–8.3] cmH2O, P < 0.001. AOP was higher in the dependent than the non-dependent ventilated lung (4.0 [2.0–6.3] vs. 3.0 [2.0–5.0] cmH2O, P < 0.001). Seventeen (47%) patients exhibited a ‘progressive change’ pattern in the pressure–time curve. These patients had a larger difference between AOPhighest and AOPglobal (3.0 [2.0–4.0] cmH2O with a maximum of 8 cmH2O) compared to the other two patterns: 1.0 [0–1.0] cmH2O in ‘no change’ , P < 0.001 and 1.0 [0–2.0] cmH2O in ‘abrupt change’ , P = 0.003. Conclusion AOPglobal mostly reflects the lowest opening pressure in the lung and frequently underestimates the highest regional AOP in mechanically ventilated patients with AHRF. A progressive slope change during the low-flow pressure–time curve indicates the presence of several and higher regional AOPs. Trial registration Clinicaltrials.gov, NCT 05825534 (registered, April 24th, 2023), retrospectively registered. Graphical abstract

Grounding Grid Electrical Impedance Imaging Method Based on an Improved Conditional Generative Adversarial Network

The grounding grid is an important piece of equipment to ensure the safety of a power system, and thus research detecting on its corrosion status is of great significance. Electrical impedance tomography (EIT) is an effective method for grounding grid corrosion imaging. However, the inverse process of image reconstruction has pathological solutions, which lead to unstable imaging results. This paper proposes a grounding grid electrical impedance imaging method based on an improved conditional generative adversarial network (CGAN), aiming to improve imaging precision and accuracy. Its generator combines a preprocessing module and a U-Net model with a convolutional block attention module (CBAM). The discriminator adopts a PatchGAN structure. First, a grounding grid forward problem model was built to calculate the boundary voltage. Then, the image was initialized through the preprocessing module, and the important features of ground grid corrosion were extracted again through the encoder module, decoder module and attention module. Finally, the generator and discriminator continuously optimized the objective function and conducted adversarial training to achieve ground grid electrical impedance imaging. Imaging was performed on grounding grids with different corrosion conditions. The results showed a final average peak signal-to-noise ratio of 20.04. The average structural similarity was 0.901. The accuracy of corrosion position judgment was 94.3%. The error of corrosion degree judgment was 9.8%. This method effectively improves the pathological problem of grounding grid imaging and improves the precision and accuracy, with certain noise resistance and universality.

Enhanced flexoelectric properties in sodium bismuth titanate-based lead-free relaxor ferroelectrics by inducing polar nanoregions

The presence of polar nanoregions (PNRs) is widely recognized as playing a crucial role in the functionalities of numerous solid dielectrics. However, the contribution of PNRs to the specific coupling between strain gradient and electric polarization (flexoelectricity) has not yet been thoroughly understood. Herein, we investigated the impact of varying PNR concentrations on the dielectric and flexoelectric properties of lead-free relaxor ferroelectric (Bi0.5Na0.5)TiO3 ceramics, achieved through stoichiometric BaTiO3 doping. The temperature-dependent dielectric properties indicated the presence of PNRs in doubly doped ceramics as compared to pure BNT. Complex impedance analysis and piezoresponse force microscopy measurements demonstrated significant differences in PNR concentrations among the different components. The reorientation of PNRs notably enhanced the flexoelectric response of the doubly doped BNT-xBT ceramics, with this enhancement being positively correlated with the concentration of PNR. Specifically, the flexoelectric coefficient was found to be approximately 10 times higher in the morphotropic phase boundary (MPB) region (x = 0.08) compared to pure BNT. These findings illustrate that adjusting the concentration of PNRs in lead-free relaxation ferroelectrics is an effective strategy for improving flexoelectric properties.

Algae extract-based nanoemulsions for photoprotection against UVB radiation: an electrical impedance spectroscopy study

Skin cancer is one of the most common types of cancer worldwide, with exposure to UVB radiation being a significant risk factor for its development. To prevent skin cancer, continuous research efforts have focused on finding suitable photoprotective ingredients from natural sources that are also environmentally friendly. This study aimed to develop oil-in-water photoprotective nanoemulsions containing marine macroalgae extract. A Box–Behnken experimental design was used to identify the most promising formulation composition, resulting in optimal physical properties. These properties, including droplet size, polydispersity index (PDI), and zeta potential, were evaluated using dynamic light scattering (DLS). To assess the photoprotection capacity of the formulations, electrical impedance spectroscopy (EIS) was employed to evaluate alterations in the electrical characteristics of excised pig skin membranes placed in Franz cells equipped with a 4-electrode set-up. The final composition of the nanoemulsion was caprylic/capric triglycerides 4%, Macrogolglycerol ricinoleate 30%, and algae extract 1%. The nanoemulsions had an average droplet size of 128.5 ± 8.6 nm, a PDI of 0.25 ± 0.06, and a zeta potential of 45.14 ± 0.02 mV. Compared to the control group, the photoprotective capacity of the oil-in-water nanoemulsions was statistically significant. Specifically, only a 15% reduction in the skin membrane electrical resistance following UVB exposure was observed when the formulation containing algae extract was used, whereas a 50% reduction was observed for the vehicle. In conclusion, this work demonstrates that the developed nanoemulsions based on natural ingredients show promising protective capacity against UVB exposure of the skin.

Detecting lung diseases with electrical impedance tomography

Detecting lung diseases with electrical impedance tomography

Early screening of lung function by electrical impedance tomography in people with normal spirometry reveals unrecognized pathological features

Early detection of lung function impairment is crucial. However, the sensitivity of spirometry in detecting early lung function deterioration is limited. In this study, lungs of 3180 healthy participants scheduled for annual health check were screened. Electrical impedance tomography measurements were conducted in 130 participants with normal spirometry for concept establishment phase and 105 for validation phase. A follow-up CT examination was suggested for participants with abnormal regional time constant or tobacco consumption ≥10 pack-years. Using CT as reference, the sensitivity and specificity of electrical impedance tomography-based screening were 81.3% and 50.0%, respectively in the concept establishment phase. In the validation phase, the sensitivity and specificity were 77.9% and 50.0%. In this study we show that conventional spirometry may not capture early changes that occur at a regional level. The regional time constant based on electrical impedance tomography can be a promising tool for early screening of lung function impairment. Clinical trial registration: ChiCTR2300076673, www.chictr.org.cn.

Three-Dimensional Electrical Impedance Imaging During Spontaneous Breathing Trials in Patients With Acute Hypoxic Respiratory Failure: A Pilot Study.

The purpose of this work is to evaluate the feasibility of lung imaging using 3D electrical impedance tomography (EIT) during spontaneous breathing trials (SBTs) in patients with acute hypoxic respiratory failure. EIT is a noninvasive, nonionizing, real-time functional imaging technique, suitable for bedside monitoring in critically ill patients. EIT data were collected in 24 mechanically ventilated patients immediately preceding and during a SBT on two rows of 16 electrodes using a simultaneous multicurrent source EIT system for 3D imaging. Dynamic 3D EIT images of conductivity were computed, as well as the EIT-derived rapid shallow breathing index, regional ventilation delay, global inhomogeneity index, and time traces of tidal volumes. 3D reconstructions and derived measures demonstrated inhomogeneity in ventilation distribution within patients. We conclude that 3D EIT images can provide information regarding ventilatory heterogeneity across the lung and may be useful in guiding ventilator management.

Stabilizing milk-derived extracellular vesicles (mEVs) through lyophilization: a novel trehalose and tryptophan formulation for maintaining structure and Bioactivity during long-term storage

Extracellular vesicles (EVs) are widely investigated for their implications in cell-cell signaling, immune modulation, disease pathogenesis, cancer, regenerative medicine, and as a potential drug delivery vector. However, maintaining integrity and bioactivity of EVs between Good Manufacturing Practice separation/filtration and end-user application remains a consistent bottleneck towards commercialization. Milk-derived extracellular vesicles (mEVs), separated from bovine milk, could provide a relatively low-cost, scalable platform for large-scale mEV production; however, the reliance on cold supply chain for storage remains a logistical and financial burden for biologics that are unstable at room temperature. Herein, we aim to characterize and engineer a freeze-dried, mEV formulation that can be stored at room temperature without sacrificing structure/bioactivity and can be reconstituted before delivery. In addition to undertaking established mEV assays of structure and function on our preparations, we introduce a novel, efficient, high throughput assay of mEV bioactivity based on Electric Cell Substrate Impedance Sensing (ECIS) in Human dermal fibroblast monolayers. By adding appropriate excipients, such as trehalose and tryptophan, we describe a protective formulation that preserves mEV bioactivity during long-term, room temperature storage. Our identification of the efficacy of tryptophan as a novel additive to mEV lyophilization solutions could represent a significant advancement in stabilizing small extracellular vesicles outside of cold storage conditions.

Rotating radial injection pattern for highly sensitive electrical impedance tomography of human lung anomalies.

Electrical Impedance Tomography (EIT) is a non-invasive technique used for lung imaging. A significant challenge in EIT is reconstructing images of deeper thoracic regions due to the low sensitivity of boundary voltages to internal conductivity variations. The current injection pattern is decisive as it influences the current path, boundary voltages, and their sensitivity to tissue changes. 
Approach. This study introduces a novel current injection pattern with radially placed electrodes excited in a rotating radial pattern. The effectiveness of the proposed pattern was investigated using a 3D computational model that mimics the human thorax, replicating its geometry and tissue electrical properties. To examine the detection of lung anomalies, models representing both healthy and unhealthy states, including cancer-like anomalies in three different positions, were developed.
The new pattern was compared to common patterns-Adjacent, Skip 1, and Opposite-using Finite Element Analysis (FEA). The comparison focused on the current density within lung nodules and the sensitivity to changes in anomaly positions. 
Main Results. Results showed that the new pattern achieved the maximum current density within anomalies compared to surrounding tissues, with peak values near the closest electrode pairs to the anomalies. Specifically, current density magnitudes reached 72.73 10^{-9} A.m, 145.24 10^{-9} A.m, and 26.43 10^{-9} A.m for the three different positions, respectively. Furthermore, the novel pattern's sensitivity to anomaly position changes surpassed the common patterns. These results demonstrate the efficiency of the proposed injection pattern in detecting lung anomalies compared to the common injection patterns.

Comparing Improvements in Biopsy Decision Making with Electrical Impedance Spectroscopy Between US and German Dermatologists

Electrical impedance spectroscopy (EIS) is a noninvasive tool that measures the electrophysical properties of pigmented lesions, generating a score to aid in the differentiation of benign and malignant lesions. This research letter compares two studies, conducted in the United States (US) and Germany, evaluating the impact of EIS on biopsy decision-making among dermatologists. Both studies used the same set of clinical and dermoscopic images along with EIS scores for 49 lesions. Findings revealed that American dermatologists had a higher rate of correct biopsy decisions for malignant melanomas (MMs) and severe dysplastic nevi (SDNs) compared to their German counterparts. However, German dermatologists showed greater accuracy in avoiding unnecessary biopsies of benign pigmented skin lesions (PSLs). The addition of both dermoscopy and EIS significantly improved biopsy decision accuracy for MMs and SDNs in both groups, with EIS further mitigating initial reductions in correct biopsy choices for benign lesions. Differences in practice patterns, training, and malpractice concerns may explain the observed variations between US and German dermatologists. These results underscore the utility of EIS as a complementary tool to dermoscopy, enhancing the accuracy of biopsy decisions and improving patient outcomes.

Effect of Ag on dielectric, elastic, electrical impedance, and Raman spectroscopic properties of CoFe2O4

Effect of Ag on dielectric, elastic, electrical impedance, and Raman spectroscopic properties of CoFe2O4

Ventilation-perfusion matching in early-stage of prone position ventilation: a prospective cohort study between COVID-19 ARDS and ARDS from other etiologies.


Prone positioning is a therapeutic strategy for severe Acute Respiratory Distress Syndrome (ARDS). In COVID-19-associated ARDS (CARDS), the application of prone position has shown varying responses, influenced by factors such as lung recruitability and SARS-CoV-2-induced pulmonary endothelial dysfunction. This study aimed to compare the early impact of pronation on lung ventilation-perfusion matching (VQmatch) in CARDS and non-COVID-19 ARDS patients (non-CARDS).

Approach:
This was a two-center, prospective study comparing between CARDS and non-CARDS. Electrical impedance tomography (EIT) was used to compare the VQmatch between supine and early-stage prone positions (~2h). The study identified the areas of Deadspace, shunt, and VQmatch. Within the defined VQmatch region, the global inhomogeneity index (VQmatch-GI) was computed to evaluate the degree of heterogeneity. Paired Wilcoxon signed-rank test and Chi-square test were used in statistical analysis.

Main results:
15 CARDS patients and 14 non-CARDS patients undergoing mechanical ventilation were included. In comparison to the non-CARDS group, the CARDS group exhibited a higher prevalence of diffuse lung disease (15 [100%] vs. 4 [28.6%], CARDS vs. Non-CARDS, p＜0.001), along with elevated SOFA score, PCO2, PEEP, and Ppeak. Among non-CARDS patients, 11/14 demonstrated improved oxygenation, whereas only 5/15 CARDS patients exhibited oxygenation improvement in prone ventilation. In 13/29 patients with oxygenation improvement (defined as above 20% increase in SpO2/FiO2), there was a significant decreased deadspace (21.3 [11.5, 33.1] vs. 9.7 [7.3, 16.9], p=0.039), and VQmatch showed an upward trend. When comparing prone ventilation to supine ventilation, non-CARDS patients showed a significant improvement in overall VQmatch (Supine 65.7 [49.7, 68.5] vs. Prone 67.4 [60.8, 72.6], p=0.019). CARDS patients had a notable decrease in ventral VQmatch (VQmatch_Ventral: Supine 35.0 [26.9, 42.0] vs. Prone 22.7 [12.4, 32.9], p=0.003), and an improvement in dorsal VQmatch (VQmatch_Dorsal: Supine 33.4 [20.4, 39.4] vs. Prone 46.4 [37.4, 48.4], p=0.031), leading to no significant improvement in overall VQmatch. Ten CARDS patients with no improvement in VQmatch had increased shunting and VQmatch-GI.

Significance:
In non-CARDS patients, the improvement in oxygenation and VQmatch following prone positioning exhibits a consistent pattern. Conversely, in CARDS patients, the impact of prone positioning reveals considerable individual variability. This study indicates that the response to short-time prone ventilation can vary in ARDS patients with different etiologies.

Trial registration: NCT05816928, 04/17/2023, retrospectively registered.

Long-term performance and stability of implanted neural interfaces in individuals with lower limb loss.

High-density nerve cuffs have been successfully utilized to restore somatosensation in individuals with lower-limb loss by interfacing directly with the peripheral nervous system. Elicited sensations via these devices have improved various functional outcomes, including standing balance, walking symmetry, and navigating complex terrains. Deploying neural interfaces in the lower limbs of individuals with limb loss presents unique challenges, particularly due to repetitive muscle contractions and the natural range of motion in the knee and hip joints for transtibial and transfemoral amputees, respectively. This study characterizes the long-term performance of these peripheral nerve interfaces, which is crucial for informing design modifications to optimize functionality. We evaluated the longitudinal performance of 16-contact nerve cuffs and their associated components implanted in four participants with unilateral transtibial limb loss over four years. Key outcome measures included charge density at sensory thresholds and electrical impedance. Out of 158 channels (i.e., individual contacts within the nerve cuffs and their corresponding leads), 63% were consistently responsive, 34% were partially responsive, and 3% were non-responsive. Smaller connector assemblies and increased lead length near the cuffs significantly enhanced performance, with the final two participants demonstrating notably improved responses where 77% and 93% of channels were consistently responsive, respectively, compared to 50% and 9% in the first two participants. Overall, the implanted nerve cuffs showed robust stability in the residual limbs of highly active individuals with limb loss. Furthermore, employing strategies to reduce stress on transition points in the components significantly improved overall system performance.

The Structural, Electrical and Dielectric Studies of CMC Based Biopolymer Gel Electrolytes for Ecofriendly Device Applications

ABSTRACTThe solution casting procedure has been effectively used to synthesize biopolymer gel electrolytes (BGEs) using carboxymethyl cellulose (CMC) and ammonium thiocyanate (NH4SCN). The XRD patterns of the bio‐based green emulsions (BGEs) have provided evidence of the non‐crystalline structure of the films. Optical micrographs of BGEs have revealed the formation of homogeneous gel electrolyte films. Complex impedance spectroscopy has been used to investigate the ion transport mechanism and dielectric relaxation dynamics of biopolymer gel electrolyte films over a wide range of temperatures. The conductivity of the gel electrolyte samples has been shown to rise with the amount of salt present. The optimum ionic conductivity, determined at room temperature, is σ = 3.97 × 10−3 Scm−1, and it is achieved in the gel electrolyte sample containing 35 wt% NH4SCN. The variation in ionic conductivity with temperature has shown a blend of Arrhenius and Vogel‐Tamman‐Fulcher (VTF) characteristics. An analysis has been conducted on the impedance data to investigate the ion transport process using the formalisms of ac conductivity, permittivity, and electric modulus. The dielectric impedance of the BGEs films has been used to determine the charge carrier density and mobility. The electrolyte with the best conductivity has shown a broad range of electrochemical stability, spanning from −1.49 to +1.27 V. The I‐t investigations has shown a high transference number (tion ~ 0.99), indicating that ions are the primary contributors to conductivity. The cyclic voltammetry tests have shown excellent reusability, indicating its potential use in devices, such as supercapacitors and rechargeable batteries.

Trying to Kill a Killer; Impressive Killing of Patient Derived Glioblastoma Cultures Using NK-92 Natural Killer Cells Reveals Both Sensitive and Highly Resistant Glioblastoma Cells.

The overall goal of this work was to assess the ability of Natural Killer cells to kill cultures of patient-derived glioblastoma cells. Herein we report impressive levels of NK-92 mediated killing of various patient-derived glioblastoma cultures observed at ET (effector: target) ratios of 5:1 and 1:1. This enabled direct comparison of the degree of glioblastoma cell loss across a broader range of glioblastoma cultures. Importantly, even at high ET ratios of 5:1, there are always subpopulations of glioblastoma cells that prove very challenging to kill that evade the NK-92 cells. Of value in this study has been the application of ECIS (Electric Cell-Substrate Impedance Sensing) biosensor technology to monitor the glioblastoma cells in real-time, enabling temporal assessment of the NK-92 cells. ECIS has been powerful in revealing that at higher ET ratios, the glioblastoma cells are acutely sensitive to the NK-92 cells, and the observed glioblastoma cell death is supported by the high-content imaging data. Moreover, long-term ECIS experiments reveal that the surviving glioblastoma cells were then able to grow and reseed the culture, which was evident 300-500 h after the addition of the NK-92 cells. This was observed for multiple glioblastoma lines. In addition, our imaging provides evidence that some NK-92 cells appear to be compromised early, which would be consistent with potent evasive mechanisms by the glioblastoma tumour cells. This research strongly highlights the potential for NK-92 cells to kill glioblastoma tumour cells and provides a basis to identify the mechanism utilised by the surviving glioblastoma cells that we now need to target to achieve maximal cytolysis of the resistant glioblastoma cells. It is survival of the highly resistant glioblastoma clones that results in tumour relapse.

Protection of liver sinusoidal endothelial cells using different preservation solutions.

Donor liver preservation methods and solutions have evolved over the last years. Liver sinusoidal endothelial cell (LSEC) barrier function and integrity during preservation is crucial for outcomes of liver transplantation. Therefore, the present study aimed to determine optimal preservation of LSEC barrier function and integrity, using different preservation solutions. Human Umbilical Vein Endothelial Cells (HUVEC) and LSEC were incubated in either University of Wisconsin machine perfusion solution (UW-MPS), histidine-tryptophan-ketoglutarate (HTK), or endothelial cell growth medium 2 (EGM2) (as a golden standard for cell culturing). Endothelial integrity was assessed by measurement of cellular morphology and expression of membrane proteins ; PECAM-1, ICAM-1, and Fc-gamma receptor CD32b (FcΥRCD32b). Endothelial barrier function was measured by electric cell-substrate impedance sensing (ECIS). Cellular respondence to inflammatory stimuli with tumor necrosis factor-alpha (TNF-α), was tested by studying trans-endothelial migration (TEM) under flow conditions. Differences in these parameters were analyzed between the different preservation solutions. PECAM-1 expression was high for all preservation solutions in HUVEC and LSEC. ICAM-1 expression was increased in both LSEC and HUVEC in all preservation solutions plus TNF-α. UW reduced PECAM-1 expression, whereas EGM2 medium promoted barrier function in LSEC and HUVEC, and monolayer recovery after wounding was best achieved in cells incubated in EGM2. LSEC and HUVEC incubated with EGM2 plus TNF-α both supported neutrophil adhesion and TEM, but much less to none when incubated in UW plus TNF-α. Overall, EGM2 showed the best results in preserving endothelial barrier function for both HUVEC and LSEC.

D-bar reconstructions with nonsmooth learned spatial priors in 2D electrical impedance tomography

D-bar reconstructions with nonsmooth learned spatial priors in 2D electrical impedance tomography

Model-based Deep Unrolling Framework for Electrical Impedance Tomography Image Reconstruction

Model-based Deep Unrolling Framework for Electrical Impedance Tomography Image Reconstruction

Electrical impedance tomography for the detection and management optimization of pulmonary embolism

Electrical impedance tomography for the detection and management optimization of pulmonary embolism

PEEP titration guided by electrical impedance tomography in critically ill mechanically ventilated patients with acute hypoxemic respiratory failure.

Positive end-expiratory pressure (PEEP) titration is crucial for improving oxygenation and preventing ventilator-induced lung injury in acute hypoxemic respiratory failure. Electrical impedance tomography (EIT) offers real-time, bedside monitoring of lung ventilation distribution, potentially guiding individualized PEEP settings.