Prone positioning allows to improve oxygenation and decrease mortality rate in COVID-19-associated acute respiratory distress syndrome (C-ARDS). However, the mechanisms leading to these effects are ...not fully understood. The aim of this study is to assess the physiologic effects of pronation by the means of CT scan and electrical impedance tomography (EIT).
Experimental, physiologic study.
Patients were enrolled from October 2020 to March 2021 in an Italian dedicated COVID-19 ICU.
Twenty-one intubated patients with moderate or severe C-ARDS.
First, patients were transported to the CT scan facility, and image acquisition was performed in prone, then supine position. Back to the ICU, gas exchange, respiratory mechanics, and ventilation and perfusion EIT-based analysis were provided toward the end of two 30 minutes steps (e.g., in supine, then prone position).
Prone position induced recruitment in the dorsal part of the lungs (12.5% ± 8.0%; p < 0.001 from baseline) and derecruitment in the ventral regions (-6.9% ± 5.2%; p < 0.001). These changes led to a global increase in recruitment (6.0% ± 6.7%; p < 0.001). Respiratory system compliance did not change with prone position (45 ± 15 vs 45 ± 18 mL/cm H2O in supine and prone position, respectively; p = 0.957) suggesting a decrease in atelectrauma. This hypothesis was supported by the decrease of a time-impedance curve concavity index designed as a surrogate for atelectrauma (1.41 ± 0.16 vs 1.30 ± 0.16; p = 0.001). Dead space measured by EIT was reduced in the ventral regions of the lungs, and the dead-space/shunt ratio decreased significantly (5.1 2.3-23.4 vs 4.3 0.7-6.8; p = 0.035), showing an improvement in ventilation-perfusion matching.
Several changes are associated with prone position in C-ARDS: increased lung recruitment, decreased atelectrauma, and improved ventilation-perfusion matching. These physiologic effects may be associated with more protective ventilation.
Defining lung recruitability is needed for safe positive end-expiratory pressure (PEEP) selection in mechanically ventilated patients. However, there is no simple bedside method including both ...assessment of recruitability and risks of overdistension as well as personalized PEEP titration.
To describe the range of recruitability using electrical impedance tomography (EIT), effects of PEEP on recruitability, respiratory mechanics and gas exchange, and a method to select optimal EIT-based PEEP.
This is the analysis of patients with coronavirus disease (COVID-19) from an ongoing multicenter prospective physiological study including patients with moderate-severe acute respiratory distress syndrome of different causes. EIT, ventilator data, hemodynamics, and arterial blood gases were obtained during PEEP titration maneuvers. EIT-based optimal PEEP was defined as the crossing point of the overdistension and collapse curves during a decremental PEEP trial. Recruitability was defined as the amount of modifiable collapse when increasing PEEP from 6 to 24 cm H
O (ΔCollapse
). Patients were classified as low, medium, or high recruiters on the basis of tertiles of ΔCollapse
.
In 108 patients with COVID-19, recruitability varied from 0.3% to 66.9% and was unrelated to acute respiratory distress syndrome severity. Median EIT-based PEEP differed between groups: 10 versus 13.5 versus 15.5 cm H
O for low versus medium versus high recruitability (
< 0.05). This approach assigned a different PEEP level from the highest compliance approach in 81% of patients. The protocol was well tolerated; in four patients, the PEEP level did not reach 24 cm H
O because of hemodynamic instability.
Recruitability varies widely among patients with COVID-19. EIT allows personalizing PEEP setting as a compromise between recruitability and overdistension. Clinical trial registered with www.clinicaltrials.gov (NCT04460859).
We investigated the effects of alternating current poling (ACP) on the piezoelectric and dielectric properties of 3-MHz sliver mode (L13 mm × W0.10-0.25 mm × T0.48 mm) vibrators fashioned from ...Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (PMN-0.30PT) single crystal (SC) plate manufactured using the continuous-feeding Bridgman (CF-BM) method for cardiac probes. The ACP SC plate (L13 mm × W24 mm × T0.48 mm) exhibited ultrahigh dielectric permittivity ( ε
/ε
) and piezoelectric coefficient ( d
) of 9690 and 2920 pC/N, respectively. After array dicing, the SC slivers with widths of 0.10, 0.15, 0.20, and 0.25 mm were obtained, and their average ε
/ε
values decreased from the SC plate ε
/ε
by 45% (5330), 29% (6880), 19% (7840), and 15% (8240), respectively, possibly because of heat and mechanical damage during the dicing. A combination of the ACP and a postdicing direct current poling (ACP-DCP) recovered their ε
/ε
values to 6050, 7080, 8140, and 8540, respectively. The sliver mode electromechanical coupling factors ( k'
) were confirmed to exceed 93% after the ACP-DCP process, which were more than 4% higher than those of DCP-DCP SC slivers. The measured impedance spectra indicated that the SC slivers with 0.10-0.20 mm in width showed no spurious mode vibration near the fundamental k'
mode. We conclude that the ACP-DCP SC slivers maintained more enhanced piezoelectric and dielectric properties than the DCP-DCP samples. These results will have important implications for the commercial application of ACP technology to medical imaging ultrasound probes.
•Electrical impedance myography (EIM) measures the volume conduction properties (VCPs) of the bulk of the muscle.•Here we introduce surface and needle EIM approaches and discuss their limitations and ...strengths.•The VCPs can serve as standardized, quantitative and objective electrophysiological biomarker of muscle.
Electrical impedance myography (EIM) technology is finding application in neuromuscular disease research as a tool to assess muscle health. Correlations between EIM outcomes, functional, imaging and histological data have been established in a variety of neuromuscular disorders; however, an analytical discussion of EIM is lacking. This review presents an explanation for clinicians and others who are applying EIM and interpreting impedance outcomes. The background of EIM is presented, including the relation between EIM, volume conduction properties, tissue structure, electrode configuration and conductor volume. Also discussed are technical considerations to guide the reader to critically evaluate EIM and understand its limitations and strengths.
Objective: To develop, and demonstrate the feasibility of, a novel image reconstruction method for absolute electrical impedance tomography (a-EIT) that pairs deep learning techniques with real-time ...robust D-bar methods and examine the influence of prior information on the reconstruction. Approach: A D-bar method is paired with a trained convolutional neural network (CNN) as a post-processing step. Training data is simulated for the network using no knowledge of the boundary shape by using an associated nonphysical Beltrami equation rather than simulating the traditional current and voltage data specific to a given domain. This allows the training data to be boundary shape independent. The method is tested on experimental data from two EIT systems (ACT4 and KIT4) with separate training sets of varying prior information. Main results: Post-processing the D-bar images with a CNN produces significant improvements in image quality measured by structural SIMilarity indices (SSIMs) as well as relative and image errors. Significance: This work demonstrates that more general networks can be trained without being specific about boundary shape, a key challenge in EIT image reconstruction. The work is promising for future studies involving databases of anatomical atlases.
Application of minimally invasive methods to enable the measurement of tissue permittivity in the neuromuscular clinic remain elusive. This paper provides a theoretical and modeling study on the ...measurement of the permittivity of two-dimensional anisotropic tissues such as skeletal muscle with a multi-electrode cross-shaped needle. For this, we design a novel cross-shaped needle with multiple-electrodes and analyse apparent impedance corresponding to the measured impedance. In addition, we propose three methods of estimate anisotropic muscle permittivity. Compared to existing electrical impedance-based needle methods that we have developed, the new needle design and numerical methods associated enable estimating in vivo muscle permittivity values with only a single needle insertion. Being able to measure muscle permittivity directly with a single needle insertion could open up an entirely new area of research with direct clinical application, including using these values to assist in neuromuscular diagnosis and to assess subtle effects of therapeutic intervention on muscle health.
Cell viability is a physiological status connected to cell membrane integrity and cytoplasmic topography, which is profoundly important for fundamental biological research and practical biomedical ...applications. A conventional method for assessing cell viability is through cell staining analysis. However, cell staining involves laborious and complicated processing procedures and is normally cytotoxic. Intrinsic cellular phenotypes thus provide new avenues for measuring cell viability in a stain-free and non-toxic manner. In this work, we present a label-free non-destructive impedance-based approach for cell viability assessment by simultaneously characterizing multiple electrical cellular phenotypes in a high-throughput manner (>1000 cells per min). A novel concept called the complex opacity spectrum is introduced for improving the discrimination of live and dead cells. The analysis of the complex opacity spectrum leads to the discovery of two frequency ranges that are optimized for characterizing membranous and cytoplasmic electrical phenotypes. The present impedance-based approach has successfully discriminated between living and dead cells in two different experimental scenarios, including mixed living and dead cells in both homogenous and heterogeneous cell samples. This impedance-based single cell phenotyping technique provides highly accurate and consistent cell viability analysis, which has been validated by commercial fluorescence-based flow cytometry (∼1% difference) using heterogeneous cell samples. This label-free high-throughput cell viability analysis strategy will have broad applications in the field of biology and medicine.
Bioimpedance at the Bedside Mulasi, Urvashi; Kuchnia, Adam J.; Cole, Abigail J. ...
Nutrition in Clinical Practice,
04/2015, Volume:
30, Issue:
2
Book Review, Journal Article
Peer reviewed
The loss of muscle mass is a defining characteristic of malnutrition, and there is ongoing interest in the assessment of lean tissue at the bedside. Globally, bioimpedance techniques have been widely ...appreciated for their noninvasiveness, safety, ease of use, portability, and relatively low cost compared with other clinically available methods. In this brief update, we review the 3 primary types of commercially available bioimpedance devices (single- and multiple-frequency and spectroscopy) and differentiate the underlying theory and current applications of each. We also address limitations and potential opportunities for using these devices at the bedside for clinical assessment. Mixed reports in the validation literature for all bioimpedance approaches have raised questions about absolute accuracy to estimate whole body composition in clinical populations, particularly those with abnormal fluid status and/or body geometry in whom underlying method assumptions may be violated. Careful selection of equations can improve whole body estimates by single- and multiple-frequency techniques; however, not all devices will allow for this approach. Research is increasing on the use of bioimpedance variables including phase angle and impedance ratio as potential markers of nutrition status and/or clinical outcomes; consensus on reference cut-points for interpreting these markers has yet to be established. Novel developments in the bioimpedance spectroscopy approach are allowing for improved fluid management in individuals receiving dialysis; these developments have implications for the clinical management of other conditions associated with fluid overload and may also provide enhanced whole body estimates of lean tissue through new modeling procedures.
Our goal was to investigate the effects of head-thorax elevation (HUP) during chest compressions (CC) on lung ventilation. A prospective study was performed on seven human cadavers. Chest was ...automatically compressed-decompressed in flat position and during progressive HUP from 18 to 35°. Lung ventilation was measured with electrical impedance tomography. In each cadaver, 5 sequences were randomly performed: one without CC at positive end-expiratory pressure (PEEP) 0cmH
O, 3 s with CC at PEEP0, 5 or 10cmH
O and 1 with CC and an impedance threshold device at PEEP0cmH
O. The minimal-to-maximal change in impedance (VT
in arbitrary unit a.u.) and the minimal impedance in every breathing cycle (EELI) the) were compared between flat, 18°, and 35° in each sequence by a mixed-effects model. Values are expressed as median (1st-3rd quartiles). With CC, between flat, 18° and 35° VT
decreased at each level of PEEP. It was 12416a.u. (10,689; 14,442), 11,239 (7667; 13,292), and 6457 (4631; 9516), respectively, at PEEP0. The same was true with the impedance threshold device. EELI/VT
significantly decreased from - 0.30 (- 0.40; - 0.15) before to - 1.13 (- 1.70; - 0.61) after the CC (P = 0.009). With HUP lung ventilation decreased with CC as compared to flat position. CC are associated with decreased in EELI.
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