Electrical impedance tomography in monitoring experimental lung injury

Objective: To apply electrical impedance tomography (EIT) and the new evaluation approach (the functional EIT) in monitoring the development of artificial lung injury. Design: Acute experimental trial. Setting: Operating room for animal experimental studies at a university hospital. Subjects: Five pigs (41.3 ± 4.1 kg, mean body weight ± SD). Interventions: The animals were anaesthetised and mechanically ventilated. Sixteen electrodes were attached on the thoracic circumference and used for electrical current injection and surface voltage measurement. Oleic acid was applied sequentially (total dose 0.05 ml/kg body weight) into the left pulmonary artery to produce selective unilateral lung injury. Measurements and results: The presence of lung injury was documented by significant changes of PaCO₂ (40.1 mmHg vs control 37.1 mmHg), PaO₂ (112.3 mmHg vs 187.5 mmHg), pH (7.35 vs 7.42), mean pulmonary arterial pressure (29.2 mmHg vs 20.8 mmHg) and chest radiography. EIT detected 1) a regional decrease in mean impedance variation over the affected left lung (–41.4 % vs control) and an increase over the intact right lung ( + 20.4 % vs control) indicating reduced ventilation of the affected, and a compensatory augmented ventilation of the unaffected lung and 2) a pronounced fall in local baseline electrical impedance over the injured lung (–20.6 % vs control) with a moderate fall over the intact lung (–10.0 % vs control) indicating the development of lung oedema in the injured lung with a probable atelectasis formation in the contralateral one. Conclusion: The development of the local impairment of pulmonary ventilation and the formation of lung oedema could be followed by EIT in an experimental model of lung injury. This technique may become a useful tool for monitoring local pulmonary ventilation in intensive care patients suffering from pulmonary disorders associated with regionally reduced ventilation, fluid accumulation and/or cell membrane changes. Received: 22 December 1997 Accepted: 7 April 1998     

Lung computed tomography during a lung recruitment maneuver in patients with acute lung injury

OBJECTIVE: To assess the acute effect of a lung recruitment maneuver (LRM) on lung morphology in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). PATIENTS: Ten patients with ALI/ARDS on mechanical ventilation. DESIGN: Prospective clinical study. SETTING: Computed tomography (CT) scan facility in a teaching hospital. INTERVENTIONS: An LRM performed by stepwise increases in positive end-expiratory pressure (PEEP) of up to 30-40 cm H(2)O. Lung basal CT sections were taken at end-expiration (patients 1 to 5), and at end-expiration and end-inspiration (patients 6 to 10). Arterial blood gases and static compliance (C(st)) were measured before, during and after the LRM. MEASUREMENTS AND MAIN RESULTS: Poorly aerated and non-aerated tissue at PEEP 10 cm H(2)O accounted for 60.0+/-29.1% of lung parenchyma, while only 1.1+/-1.8% was hyperinflated. Increasing PEEP to 20 and 30 cm H(2)O, compared to PEEP 10 cm H(2)O, decreased poorly aerated and non-aerated tissue by 16.2+/-28.0% and 33.4+/-13.8%, respectively ( p<0.05). This was associated with an increase in PaO(2) and a decrease in total static compliance. Inspiration increased alveolar recruitment at all PEEP levels. Hyperinflated tissue increased up to 2.9+/-4.0% with PEEP 30 cm H(2)O, and to a lesser degree with inspiration. No barotrauma or severe hypotension occurred. CONCLUSIONS: Lung recruitment maneuvers improve oxygenation by expanding collapsed alveoli without inducing too much hyperinflation in ALI/ARDS patients. An LRM during the CT scan gives morphologic and functional information that could be useful in setting ventilatory parameters.     

Electrical impedance tomography compared to positron emission tomography for the measurement of regional lung ventilation: an experimental study

Introduction  

Electrical impedance tomography (EIT), which can assess regional lung ventilation at the bedside, has never been compared with positron-emission tomography (PET), a gold-standard to quantify regional ventilation. This experiment systematically compared both techniques in injured and non-injured lungs.     

Estimation of regional lung volume changes by electrical impedance pressures tomography during a pressure-volume maneuver

OBJECTIVE: To assess the degree of linearity between lung volume and impedance change by electrical impedance tomography (EIT) in pigs with acute lung injury and to investigate regional impedance changes during a pressure-volume maneuver. DESIGN AND SETTING: Experimental animal study in a university research laboratory. PATIENTS AND PARTICIPANTS: Nine pigs with lung injury induced by lung lavage. INTERVENTIONS: The lungs were insufflated to four different lung volumes. Next the lungs were inflated in steps up to 40 cm H(2)O and then in steps deflated. MEASUREMENTS AND RESULTS: EIT measurements were performed. Impedance was highly linear with lung volume ( r(2)=0.97). From the pressure-volume maneuver regional pressure-impedance (P-I) curves were obtained in the upper half (ventral) and lower half (dorsal) of the thoracic cross-section. Excellent fit was found of the regional P-I curves with a predefined sigmoid equation ( r(2)=0.998). The P-I curves after lavage were markedly different than before lavage. The P-I curves recorded after lavage displayed a strong heterogeneity on the inflation limb: Lower corner pressure (traditionally lower inflection point) was significantly higher in the dorsal (28.3+/-4.1 cm H(2)O) than in the ventral region (17.5+/-4.3 cm H(2)O). The deflation limb displayed a more homogeneous pattern. Upper corner pressure and true inflection point, where the curve slope is maximal, in the dorsal region were only slightly higher than in the ventral region (1-2 cm H(2)O). CONCLUSIONS: EIT and automated curve fitting provide information on regional lung inflation and deflation which may be of clinical use for optimizing ventilator settings.     

电阻抗断层成像技术在呼吸系统肺功能成像中的应用

电阻抗断层成像技术（EIT）作为一项新兴的功能性成像技术,具有无损伤、便携、图像监护等突出特点。其中肺功能成像为目前EIT最主要的应用领域,可以实现肺通气及血流灌注的实时动态监测。本文介绍肺EIT在呼吸系统常见疾病如急性呼吸窘迫综合征、慢性阻塞性肺疾病、肺栓塞等疾病中的基础及临床研究进展,为未来EIT技术的进步及临床应用提供帮助。     

Electrical impedance measured changes in thoracic fluid content during thoracentesis

Summary. In patients (seven females and 11 males) with pleural effusion due to pulmonary (n= 13) or cardiac disease (n= 5) the change in baseline transthoracic impedance (Z₀) was measured by electrical impedance (BoMed's NCCOM-3, 70 kHz) during thoracentesis. Data were obtained before and after withdrawal of each 500 ml, and at the end of the thoracentesis. We found a close linear correlation (r= 0–97) between changes in Z₀ and the volume of aspirated pleural effusion (y= 0–415 x+0–093). The variability of the estimated thoracic fluid volumes was analysed with a plot of the residuals from the regression line, and we found that changes in thoracic fluid volume estimated by impedance technique would be within ± 302 ml (=2 SD). However, the absolute value of Z₀ before thoracentesis could not differentiate the group of patients with pleural effusion from normal subjects (n= 28).     

A patient with a transient high-density area on computed tomography in juvenile lung injury

An 8-year-old boy was struck by a truck, and the impact carried him 10 m away from the scene. On arrival at the hospital, his chest and left thigh roentgenograms revealed fractures of the left clavicle, scapular, and left femur shaft. His chest computed tomography scan demonstrated right dominant bilateral multiple ill-defined and hazy ground-glass density areas 70 minutes after the accident. He was treated with conservative therapy with 2 L/min of oxygen. On the fourth hospital day, the chest computed tomography scan revealed the disappearance of most of the pulmonary lesions. Based on the natural time course of pulmonary contusions, it was impossible to explain why most of the pulmonary lesions in this patient disappeared within 4 days. A transient malfunction of the blood-gas barrier in the alveoli induced by blunt trauma might lead to the generation of lung edema.     

Electrical impedance tomography measured at two thoracic levels can visualize the ventilation distribution changes at the bedside during a decremental positive end-expiratory lung pressure trial

Introduction  

Computed tomography of the lung has shown that ventilation shifts from dependent to nondependent lung regions. In this study, we investigated whether, at the bedside, electrical impedance tomography (EIT) at the cranial and caudal thoracic levels can be used to visualize changes in ventilation distribution during a decremental positive end-expiratory pressure (PEEP) trial and the relation of these changes to global compliance in mechanically ventilated patients.     

Intercomparison of recruitment maneuver efficacy in three models of acute lung injury

OBJECTIVE: To compare the relative efficacy of three forms of recruitment maneuvers in diverse models of acute lung injury characterized by differing pathoanatomy. DESIGN: We compared three recruiting maneuver (RM) techniques at three levels of post-RM positive end-expiratory pressure in three distinct porcine models of acute lung injury: oleic acid injury; injury induced purely by the mechanical stress of high-tidal airway pressures; and pneumococcal pneumonia. SETTING: Laboratory in a clinical research facility. SUBJECTS: Twenty-eight anesthetized mixed-breed pigs (23.8 +/- 2.6 kg). INTERVENTIONS: The RM techniques tested were sustained inflation, extended sigh or incremental positive end-expiratory pressure, and pressure-controlled ventilation. PRIMARY MEASUREMENTS: Oxygenation and end-expiratory lung volume. MAIN RESULTS: The post-RM positive end-expiratory pressure level was the major determinant of post-maneuver PaO2, independent of the RM technique. The pressure-controlled ventilation RM caused a lasting increase of PaO2 in the ventilator-induced lung injury model, but in oleic acid injury and pneumococcal pneumonia, there were no sustained oxygenation differences for any RM technique (sustained inflation, incremental positive end-expiratory pressure, or pressure-controlled ventilation) that differed from raising positive end-expiratory pressure without RM. CONCLUSIONS: Recruitment by pressure-controlled ventilation is equivalent or superior to sustained inflation, with the same peak pressure in all tested models of acute lung injury, despite its lower mean airway pressure and reduced risk for hemodynamic compromise. Although RM may improve PaO2 in certain injury settings when traditional tidal volumes are used, sustained improvement depends on the post-RM positive end-expiratory pressure value.     

Electrical impedance tomography (EIT) in applications related to lung and ventilation: a review of experimental and clinical activities

This review article is a summary of the publications dealing with the pulmonary applications of electrical impedance tomography (EIT). Original papers on EIT lung imaging published over 15 years are analysed and several aspects of the performed EIT measurements summarized. Information on the type of the EIT device and electrodes used, the studied transverse thoracic planes, the data acquisition rate, the number of studied animals, normal subjects or patients, the kind of lung pathology, the performed ventilatory manoeuvres and other interventions, as well as the applied reference techniques, is given. The type of the generated pulmonary EIT images and the quantitative analysis of the EIT data are described. Finally, the major results achieved are presented, followed by an analysis of the perspectives of EIT in clinical applications. A comparative analysis of the EIT hardware and the quality of the evaluation tools was not performed.     

Alveolar recruitment assessed by positron emission tomography during experimental acute lung injury

Objectives To compare changes in aerated lung volumes measured by positron emission tomography (PET) and inflation volume-pressure curve (V – P) of the respiratory system, and to evaluate the reliability of PET to assess alveolar recruitment.Design and setting Experimental study in six anesthetized and mechanically ventilated pigs in a PET facility in an experimental university laboratory.Interventions Lung injury was induced by oleic acid. Animals were randomly studied in four conditions: PEEP 0 cmH₂O (ZEEP) in supine position (SP), PEEP 10 cmH₂O in SP, ZEEP in prone position (PP) and PEEP in PP, each applied for 30 min.Measurements and results With PET aerated lung volume was obtained from pulmonary density analysis using transmission scan (VA_trans) and from nitrogen-13 kinetics on emission scan (VA_em). Changes in VA_trans and VA_em were computed as the difference in aerated volume between conditions. VA_trans and VA_em did not differ between SP and PP, on either ZEEP or PEEP, suggesting no modification in relaxation volume of the respiratory system induced by posture. Changes in VA_trans or VA_em were significantly correlated with changes in aerated volume assessed from superimposed V – P curves (R ² = 0.74 and 0.75, respectively). Alveolar recruitment assessed by PET was significantly correlated with both PaO₂ (R ² = 0.61) and PaCO₂ (R ² = 0.40) variations induced by PEEP.Conclusions PET is a new reliable tool of scientific interest to image lung volume and alveolar recruitment during acute lung injury.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.This research was supported by the Hospices civils de Lyon.This article is discussed in the editorial available at:     

Dynamic computed tomography: a novel technique to study lung aeration and atelectasis formation during experimental CPR

OBJECTIVE: To develop an image based technique to study the effect of different ventilatory strategies on lung ventilation and alveolar recruitment during cardiopulmonary resuscitation (CPR). DESIGN: (1) Technical development of the following components: (a) construction of an external chest compression device, which does not interfere with CT imaging, and (b) development of a software tool to detect lung parenchyma automatically and to calculate radiological density parameters. (2) Feasibility studies: three strategies of CPR ventilation were performed and imaged in one animal each (pigs, 25 kg): volume-constant ventilation (VCV), no ventilation, or continuous airway pressure (CPAP). One minute after induction of circulatory arrest inside the CT scanner, external chest compressions started at a rate of 100 cpm, and one of the ventilation modes was initiated. After 1 min, intravenous epinephrine was added as a bolus (40 microg/kg), followed by a continuous infusion (13 microg/kg per min). Six minutes later, dynamic CT acquisitions (temporal resolution: 100 ms) commenced. Simultaneously, arterial blood gases, acid base status and haemodynamics were sampled. RESULTS: Using a modified chest compression device, dynamic CT acquisitions are feasible during closed-chest CPR. In three pilot experiments with different ventilation strategies, the dedicated software tool allowed to quantify ventilated, atelectatic and over-distended fractions of total lung area. VCV showed a large amount of atelectasis, which was recruited during every respiratory cycle. No ventilation led to atelectasis to govern over 50% of the total lung area. CPAP caused less atelectasis as VCV, and no cyclic recruitment and de-recruitment phenomena were observed. CONCLUSIONS: We demonstrate a novel experimental set up, which allows quantification of different lung compartments during ongoing CPR and may become useful in comparing the direct pulmonary effects of different ventilatory strategies in the settings of Basic and Advanced Cardiac Life Support.     

Regional pressure volume curves by electrical impedance tomography in a model of acute lung injury

OBJECTIVE: A new noninvasive method, electrical impedance tomography (EIT), was used to make pressure-impedance (PI) curves in a lung lavage model of acute lung injury in pigs. The lower inflection point (LIP) and the upper deflection point (UDP) were determined from these curves and from the traditional pressure-volume (PV) curves to determine whether the PI curves resemble the traditional PV curves. Furthermore, regional differences in the mentioned determinants were investigated. DESIGN: Prospective, experimental study. SETTING: Animal research laboratory. INTERVENTIONS: In nine anesthetized pigs, repeated lung lavage was performed until a Pao2 <80 torr was reached. Thereafter, an inspiratory PV curve was made using a constant flow of oxygen. During the intervention, EIT measurements were performed. MEASUREMENTS AND MAIN RESULTS: In this study, the LIP(EIT) was within 2 cm H2O of the LIP(PV). Furthermore, it was possible to visualize regional PI curves by EIT. No significant difference was found between the LIP(PV) (21.3+/-3.0 cm H2O) and the LIP(EIT) of the total lung (21.5+/-3.0 cm H2O) or the anterior parts of the lung (21.5+/-2.9 cm H2O). A significantly higher LIP (29.5+/-4.9 cm H2O) was found in the posterior parts of the lung. A UDP(PV) could be found in three animals only, whereas in all animals a UDP(EIT) could be determined from the anterior part of the lung. CONCLUSIONS: Using EIT, determination of LIP and UDP from the regional PI curves is possible. The obtained information from the regional PI curves may help in understanding alveolar recruitment. The use of this new bedside technique for clinical decision making remains to be examined.     

Electrical impedance tomography applied to assess matching of pulmonary ventilation and perfusion in a porcine experimental model

Introduction  

Electrical impedance tomography (EIT) can be used to measure impedance changes related to the thoracic content of air and blood. Few studies, however, have utilised EIT to make concurrent measurements of ventilation and perfusion. This experimental study was performed to investigate the feasibility of EIT to describe ventilation/perfusion (V/Q) matching after acute changes of pulmonary perfusion and aeration.     

Monitoring of recruitment and derecruitment by electrical impedance tomography in a model of acute lung injury

OBJECTIVE: To evaluate a noninvasive system for obtaining information about alveolar recruitment and derecruitment in a model of acute lung injury. DESIGN: Prospective experimental study. SETTING: Animal research laboratory. SUBJECTS: Nine anesthetized pigs. INTERVENTIONS: Electrical impedance tomography measurements were performed. Electrical impedance tomography is an imaging technique that can register the ventilation-induced impedance changes in different parts of the lung. In nine anesthetized pigs, repeated lung lavages were performed until a PaO2 of <80 mm Hg was reached. Thereafter, the lungs were recruited according to two different recruitment protocols: the open lung approach and the open lung concept. Five time points for measurements were chosen: healthy (reference), lavage (atelectasis), recruitment, derecruitment, and maintain recruited (final). MEASUREMENTS AND MAIN RESULTS: After lavage, there was a significant increase in the impedance ratio, defined as the ventilation-induced impedance changes of the anterior part of the lung divided by that of the posterior part (from 1.75 +/- 0.63 to 4.51 +/- 2.22; p < .05). The impedance ratio decreased significantly after performing the recruitment protocol (from 4.51 +/- 2.22 to 1.18 +/- 0.51). During both recruitment procedures, a steep increase in baseline impedance change was seen. Furthermore, during derecruitment, a decrease in the slope in baseline impedance change was seen in the posterior part of the lung, whereas the anterior part showed no change. CONCLUSION: Electrical impedance tomography is a technique that can show impedance changes resembling recruitment and derecruitment of alveoli in the anterior and posterior parts of the lung. Therefore, electrical impedance tomography may help in determining the optimal mechanical ventilation in a patient with acute lung injury.     

Effect of a lung recruitment maneuver by high-frequency oscillatory ventilation in experimental acute lung injury on organ blood flow in pigs

Introduction  

The objective was to study the effects of a lung recruitment procedure by stepwise increases of mean airway pressure upon organ blood flow and hemodynamics during high-frequency oscillatory ventilation (HFOV) versus pressure-controlled ventilation (PCV) in experimental lung injury.     

The assessment of regional lung mechanics with electrical impedance tomography: a pilot study during recruitment manoeuvres

Objective  The purpose of lung recruitment manoeuvres is to open collapsed lung regions, improve gas exchange and optimise regional lung mechanics. This study investigates the efficacy of recruitment manoeuvres for improving regional ventilation distribution as characterised using electrical impedance tomography (EIT). Design, subjects, interventions  A ventilated ovine smoke inhalation lung injury model was used. Respiratory mechanics and regional filling capacity of the lung were measured using EIT pre- and post- recruitment and compared to a control group. Measurements  EIT, expressed as the time course relation of the regional versus the global impedance change, measured the regional filling capacities of the lung. Main results  After smoke inhalation injury, the dependent lung showed a significantly larger area of collapse and a reduced filling capacity compared to the non-dependent lung. After recruitment the ventilated volume increased and the dependent lung showed improved respiratory mechanics, whereas the non-dependent lung was more likely to be hyper-inflated during tidal breathing. Conclusions  Lung recruitment manoeuvres have a significant impact on regional lung mechanics and individual measurement of ventilation distribution using EIT may assist to improve ventilatory management. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.