Electrical Impedance Tomography Signal Research Articles

Improvement ability of EIT for Thermal monitoring during Thermal Therapy by gold nanoparticles

Introduction: To prevention the healthy tissues from irreversible damages, monitoring the temperature variation of healthy tissues is critical parameter during thermal therapies. Electrical impedance tomography (EIT) is considered as a real time imaging modality for monitoring the temperature but researches show that it suffers from low temperature resolution. In this study using of gold nanoparticles(GNPs) to increase the EIT signal variation due to change in temperature of tissues was studied and improvement of its temperature resolution was surveyed. Materials and Methods: Spherical GNPs with size of 20-25 nm were synthesized with Turkevich method. Size distribution and shape of these NPs was characterized by transmission electron microscopy (TEM). EI of muscle and fat tissues at different temperatures were measured and compared to their EI at presence of GNPs. Results: EI of tissues decrease (electrical conductance increase) as their temperature increase and GNPs cause to intensify this phenomenon. Increase in specific conductance of fat and muscle tissues at 360 C were 3.80´10-3 S m and 8.59´10-2 S m, respectively. These values were 15.1% and 13.2% for fat and muscle tissues, respectively. Conclusion: Presence of GNPs could lead to increase the variation of EIT signal intensity due to change of temperature. Therefore, considering the temperature changes followed to use of GNPs in thermal treatment is recommended.

A High Frame Rate Wearable EIT System Using Active Electrode ASICs for Lung Respiration and Heart Rate Monitoring

A high specification, wearable, electrical impedance tomography (EIT) system with 32 active electrodes is presented. Each electrode has an application specific integrated circuit (ASIC) mounted on a flexible printed circuit board, which is then wrapped inside a disposable fabric cover containing silver-coated electrodes to form the wearable belt. It is connected to a central hub that operates all the 32 ASICs. Each ASIC comprises a high-performance current driver capable of up to 6 mAp-p output, a voltage buffer for EIT and heart rate signal recording as well as contact impedance monitoring, and a sensor buffer that provides multi-parameter sensing. The ASIC was designed in a CMOS 0.35- $\mu \text{m}$ high-voltage process technology. It operates from ±9 V power supplies and occupies a total die area of 3.9 mm2. The EIT system has a bandwidth of 500 kHz and employs two parallel data acquisition channels to achieve a frame rate of 107 frames/s, the fastest wearable EIT system reported to date. Measured results show that the system has a measurement accuracy of 98.88% and a minimum EIT detectability of 0.86 $\Omega $ /frame. Its successful operation in capturing EIT lung respiration and heart rate biosignals from a volunteer is demonstrated.

Thoracic electrical impedance tomography: an adaptive monitor for dynamic organs

Electrical impedance tomography (EIT) is increasingly used in intensive care patients to monitor pulmonary and cardiac function non-invasively at the bedside. Impedance variations measured by EIT due to a change in thoracic air content represent the largest and most studied signal, allowing the measurement of end-expiratory lung volume (EELV), global and regional ventilation and spatial and temporal heterogeneity of ventilation distribution. This technique gives a dynamic, repeatable, global and regional description of the respiratory system mechanics, providing at the same time a dynamic picture of lung function. A smaller but detectable change in electrical impedance is due to the increase/decrease of blood content into lung vascular tree during the cardiac cycle. This signal is used to measure stroke volume and global and regional lung perfusion. The integration of the ventilation and perfusion components of the EIT signal can be used to measure ventilation-perfusion matching. The aim of this review is to describe the current clinical applications of EIT, providing a guide to the most relevant physiologic variables derived from EIT and their clinical meaning. We will focus on respiratory and cardiac-related variables and their application in both the anesthetized and awake patients. A special attention will be given to two greatly expanding fields of use: pediatric patients and the perioperative (adult and pediatric) setting. Finally, we will describe potential future applications which we expect will soon become a reality, with the potential to change our everyday practice in the intensive care unit and the operating theatre.

T16. Imaging propagation of ictal spike-and-wave activity in the cerebral cortex over milliseconds with fast neural electrical impedance tomography

Introduction Electrical Impedance Tomography (EIT) is an emerging medical imaging modality in which the internal impedance of a subject can be imaged using boundary voltage measurements from non-penetrating surface electrodes. It can be used to image neuronal depolarisation over milliseconds as impedance falls when ion channels open during neuronal depolarization. EIT of fast electrical activity due to neuronal depolarisation in the rat cerebral cortex has previously been undertaken with a resolution of 2 ms and μ m using epicortical electrode arrays during evoked potentials and interictal spikes. The purpose of the current work was to use EIT to image ictal spike-wave discharges (SWDs) in the rat cortex and examine the possibility of determining the propagation pattern of this activity through cortical layers. Methods Adult female Sprague-Dawley rats (300–450 g) were anaesthetised with isoflurane; anaesthesia was maintained after surgery with isoflurane and intravenous fentanyl. A large craniotomy was performed on one hemisphere before implanting a 15 × 9 mm257-electrode array, fabricated from stainless steel and silicone rubber, on the cortical surface. Epileptiform events were induced by electrically stimulating the sensorimotor cortex with a 5-s train of 1–2 mA biphasic, charge-balanced square-wave pulses at 100 Hz. For EIT recordings, a 50 μ A sine-wave was injected at 1.7 kHz through a different electrode pair for each of ∼ 30 seizures. EIT images were produced with trigger markers at the peak amplitude of SWDs in the ECoG, averaging over time within one seizure, and over different current pair applications for successive seizures, demodulation of the EIT signal with a ± 500 Hz bandwidth and reconstruction of the processed voltages to produce images with a resolution of 300 μ m and Results There was a maximum impedance change of −0.31 ± 0.06% during the spike phase of averaged SWDs, the early focus of which was spatially confined to the infragranular layers of the primary somatosensory cortex (p Conclusion Fast neural EIT is a novel method which permits visualisation of the trajectory of propagation of ictal activity over milliseconds through the cerebral cortex. This has potential for improving understanding of the pathophysiology of such paroxysmal events and tracking the trajectory of ictal activity throughout the brain in 3D. This could provide a complementary clinical tool to help localise the epileptogenic zone in treatment-resistant focal epilepsies during presurgical evaluation.

Regional distribution of ventilation in horses in dorsal recumbency during spontaneous and mechanical ventilation assessed by electrical impedance tomography: a case series

ObjectiveTo evaluate the regional distribution of ventilation in horses during spontaneous breathing and controlled mechanical ventilation (CMV) using electrical impedance tomography (EIT). Study designProspective, experimental case series. AnimalsFour anaesthetized experimental horses. MethodsHorses were anaesthetized with isoflurane in an oxygen-air mixture and medetomidine continuous rate infusion, placed in dorsal recumbency with an EIT belt around the thorax, and allowed to breathe spontaneously until PaCO2 reached 13.3 kPa (100 mmHg), when volume CMV was started. For each horse, the EIT signal was recorded for at least 2 minutes immediately before (T1), and at 30 (n = 3) or 60 (n = 1) minutes after the start of CMV (T2). The centre of ventilation (CoV), dependent silent spaces (DSS) (likely to represent atelectatic lung areas), non-dependent silent spaces (NSS) (likely to represent lung areas with low ventilation) and total ventilated area (TVA) were evaluated. Cardiac output (CO) was measured and venous admixture and oxygen delivery (DO2) were calculated at T1 and T2. Data are presented as median and range. ResultsAfter the initiation of CMV, the CoV moved ventrally towards the non-dependent lung by 10% [from 57.4% (49.6–60.2%) to 48.3% (41.9–54.4%)]. DSS increased [from 4.1% (0.2–13.9%) to 18.7% (7.5–27.5%)], while NSS [21.7% (9.4–29.2%) to 9.9% (1.0–20.7%)] and TVA [920 (699–1051) to 837 (662–961) pixels] decreased. CO, venous admixture and DO2 also decreased. Conclusions and clinical relevanceIn spontaneously breathing anaesthetized horses in dorsal recumbency, ventilation was essentially centred within the dependent dorsal lung regions and moved towards non-dependent ventral regions as soon as CMV was started. This shows a major lack of ventilation in the dependent lung, which may be indicative of atelectasis.

Non-invasive monitoring of pulmonary artery pressure from timing information by EIT: experimental evaluation during induced hypoxia

Monitoring of pulmonary artery pressure (PAP) in pulmonary hypertensive patients is currently limited to invasive solutions. We investigate a novel non-invasive approach for continuous monitoring of PAP, based on electrical impedance tomography (EIT), a safe, low-cost and non-invasive imaging technology. EIT recordings were performed in three healthy subjects undergoing hypoxia-induced PAP variations. The pulmonary pulse arrival time (PAT), a timing parameter physiologically linked to the PAP, was automatically calculated from the EIT signals. Values were compared to systolic PAP values from Doppler echocardiography, and yielded strong correlation scores () for all three subjects. Results suggest the feasibility of non-invasive, unsupervised monitoring of PAP.

Assessment of distribution of ventilation by electrical impedance tomography in standing horses

The aim was to evaluate the feasibility of using electrical impedance tomography (EIT) in horses. Thoracic EIT was used in nine horses. Thoracic and abdominal circumference changes were also measured with respiratory ultrasound plethysmography (RUP). Data were recorded during baseline, rebreathing of CO2 and sedation. Three breaths were selected for analysis from each recording. During baseline breathing, horses regularly took single large breaths (sighs), which were also analysed. Functional EIT images were created using standard deviations (SD) of pixel signals and correlation coefficients (R) of each pixel signal with a reference respiratory signal. Left-to-right ratio, centre-of-ventilation and global-inhomogeneity-index were calculated. RM-ANOVA and Bonferroni tests were used (P < 0.05). Distribution of ventilation shifted towards right during sighs and towards dependent regions during sighs, rebreathing and sedation. Global-inhomogeneity-index did not change for SD but increased for R images during sedation. The sum of SDs for the respiratory EIT signals correlated well with thoracic (r2 = 0.78) and abdominal (r2 = 0.82) tidal circumferential changes. Inverse respiratory signals were identified on the images at sternal location and based on reviewing CT images, seemed to correspond to location of gas filled intestines. Application of EIT in standing non-sedated horses is feasible. EIT images may provide physiologically useful information even in situations, such as sighs, that cannot easily be tested by other methods.

Aortic blood pressure measured via EIT: investigation of different measurement settings

Electrical impedance tomography (EIT) allows the measurement of intra-thoracic impedance changes related to cardiovascular activity. As a safe and low-cost imaging modality, EIT is an appealing candidate for non-invasive and continuous haemodynamic monitoring. EIT has recently been shown to allow the assessment of aortic blood pressure via the estimation of the aortic pulse arrival time (PAT). However, finding the aortic signal within EIT image sequences is a challenging task: the signal has a small amplitude and is difficult to locate due to the small size of the aorta and the inherent low spatial resolution of EIT. In order to most reliably detect the aortic signal, our objective was to understand the effect of EIT measurement settings (electrode belt placement, reconstruction algorithm). This paper investigates the influence of three transversal belt placements and two commonly-used difference reconstruction algorithms (Gauss–Newton and GREIT) on the measurement of aortic signals in view of aortic blood pressure estimation via EIT. A magnetic resonance imaging based three-dimensional finite element model of the haemodynamic bio-impedance properties of the human thorax was created. Two simulation experiments were performed with the aim to (1) evaluate the timing error in aortic PAT estimation and (2) quantify the strength of the aortic signal in each pixel of the EIT image sequences. Both experiments reveal better performance for images reconstructed with Gauss–Newton (with a noise figure of 0.5 or above) and a belt placement at the height of the heart or higher. According to the noise-free scenarios simulated, the uncertainty in the analysis of the aortic EIT signal is expected to induce blood pressure errors of at least ± 1.4 mmHg.

Recent advances in and limitations of cardiac output monitoring by means of electrical impedance tomography.

Currently, the monitoring of cardiac output (CO) and stroke volume (SV) is mainly performed using invasive techniques. Therefore, performing CO monitoring noninvasively by means of electrical impedance tomography (EIT) would be advantageous for intensive care. Our hypothesis was that, by means of EIT, it is possible to assess heart rate (HR) and to quantify changes in SV due to changes in ventilator settings. CO (HR and SV) of 14 pigs (32-40 kg body weight) was changed by incremental increases in positive end-expiratory pressure levels (0, 5, 10, 15, and 20 cm·H2O; ramp maneuver). This ramp maneuver was applied 4 times in each animal, yielding 43 evaluable single experiments. At each positive end-expiratory pressure level, SV was assessed by transpulmonary thermodilution using a PiCCO device. EIT data were acquired using a Dräger EIT Evaluation Kit 2. The EIT-based SV-related signal, Z(SV) (in [AU]), showed only a weak correlation (after excluding 2 measurements) with SV(TTD) of r = 0.58 (95% confidence interval, 0.43-0.71). If Z(SV) is calibrated by the reference 1 time for each experiment (defined as SVEIT), the correlation is approximately 0.85 (95% confidence interval, 0.78-0.90). A possible reason for the moderate correlation is the unexpected scaling pattern, leading to amplification of the cardiac impedance signal, found in some animals. The scaling is probably due to the imperfect reconstruction (i.e., a change of sensitivity) of the EIT images or to a change in the position of the heart. The hypothesis that EIT can be used to monitor CO and SV was confirmed, but further studies are required before this technique can be applied in clinical practice. HR was determined robustly and accurately. For SV monitoring, promising results were obtained in 80% of the experiments. However, unexpected scaling of the cardiac EIT signal causing inaccurate estimation of SV remains an issue. Before robust assessment of SV by EIT is suitable for clinical practice, the cause of and compensation for undesired scaling effects need to be investigated.

Unilateral empyema impacts the assessment of regional lung ventilation by electrical impedance tomography

Several studies have shown the ability of electrical impedance tomography (EIT) to assess regional ventilation distribution in human lungs. Fluid accumulation in the pleural space as in empyema, typically occurring on one chest side, may influence the distribution of ventilation and the corresponding EIT findings. The aim of our study was to examine this effect on the assessment of regional ventilation by EIT. Six patients suffering from unilateral empyema and intubated with a double-lumen endotracheal tube were studied. EIT data were acquired during volume-controlled ventilation with bilateral (tidal volume (VT): 800 ml) and unilateral ventilation (VT: 400 ml) of the right and left lungs. Mean tidal amplitudes of the EIT signal were calculated in all image pixels. The sums of these values, expressed as relative impedance change (rel. ΔZ), were then determined in whole images and functionally defined regions-of-interest (ROI). The sums of rel. ΔZ calculated during the two cases of one-lung ventilation either on the affected or unaffected side were significantly smaller than during bilateral ventilation. However, in contrast to previous findings in patients with no pleural pathology, very low values of rel. ΔZ were found when the lung on the affected side was ventilated. ROI-based analysis rendered higher values than the whole-image analysis in this case, nonetheless, the values were significantly smaller than when the unaffected side was ventilated in spite of identical VT. In conclusion, our results indicate that the presence of empyema may affect the quantitative evaluation of regional lung ventilation by EIT.

Ventilation and cardiac related impedance changes in children undergoing corrective open heart surgery

Electrical impedance tomography (EIT) can determine ventilation and perfusion relationship. Most of the data obtained so far originates from experimental settings and in healthy subjects. The aim of this study was to demonstrate that EIT measures the perioperative changes in pulmonary blood flow after repair of a ventricular septum defect in children with haemodynamic relevant septal defects undergoing open heart surgery. In a 19 bed intensive care unit in a tertiary children's hospital ventilation and cardiac related impedance changes were measured using EIT before and after surgery in 18 spontaneously breathing patients. The EIT signals were either filtered for ventilation (ΔZV) or for cardiac (ΔZQ) related impedance changes. Impedance signals were then normalized (normΔZV, normΔZQ) for calculation of the global and regional impedance related ventilation perfusion relationship (normΔZV/normΔZQ). We observed a trend towards increased normΔZV in all lung regions, a significantly decreased normΔZQ in the global and anterior, but not the posterior lung region. The normΔZV/normΔZQ was significantly increased in the global and anterior lung region. Our study qualitatively validates our previously published modified EIT filtration technique in the clinical setting of young children with significant left-to-right shunt undergoing corrective open heart surgery, where perioperative assessment of the ventilation perfusion relation is of high clinical relevance.

Transrectal electrical impedance tomography of the prostate: Spatially coregistered pathological findings for prostate cancer detection

Prostate cancer ranks as one of the most common malignancies and currently represents the second leading cancer-specific cause of death in men. The current use of single modality transrectal ultrasound (TRUS) for biopsy guidance has a limited sensitivity and specificity for accurately identifying cancerous lesions within the prostate. This study introduces a novel prostate cancer imaging method that combines TRUS with electrical impedance tomography (EIT) and reports on initial clinical findings based on in vivo measurements. The ultrasound system provides anatomic information, which guides EIT image reconstruction. EIT reconstructions are correlated with semiquantitative pathological findings. Thin plate spline warping transformations are employed to overlay electrical impedance images and pathological maps describing the spatial distribution of prostate cancer, with the latter used as reference for data analysis. Clinical data were recorded from a total of 50 men prior to them undergoing radical prostatectomy for prostate cancer treatment. Student's t-tests were employed to statistically examine the electrical property difference between cancerous tissue and benign tissue as defined through histological assessment of the excised gland. Example EIT reconstructions are presented along with a statistical analysis comparing EIT and pathology. An average transformation error of 1.67% is found when 381 spatially coregistered pathological images are compared with their target EIT reconstructed counterparts. At EIT signal frequencies of 0.4, 3.2, and 25.6 kHz, paired-testing demonstrated that the conductivity of cancerous regions is significantly greater than that of benign regions ( p < 0.0304). These preliminary clinical findings suggest the potential benefits electrical impedance measurements might have for prostate cancer detection.

Electrical Impedance Tomography in Acute Respiratory Distress Syndrome

Electrical impedance tomography (EIT) is an emerging new imaging modality not yet routinely used in a clinical setting. The generation of EIT scans is based on the non-invasive measurement of electrical properties of tissues which does not require the use of radiation. Thoracic EIT examinations have been shown to track changes in regional lung volumes at scan rates of up to 40-50 scans/s. Experimental and clinical studies indicate the potential of EIT in monitoring regional lung ventilation and aeration at the bedside. Mechanically ventilated patients with acute lung injury and acute respiratory distress syndrome (ARDS) might benefit from possible continuous monitoring of their regional lung function by EIT which could be used to optimise the ventilator settings and minimise the ventilator-induced lung injury. This review explains the measuring principle of EIT and the analysis of regional EIT signals which allow the assessment of regional lung ventilation, aeration and potentially also lung perfusion. Protective lung ventilation using low tidal volumes and adequate positive end-expiratory pressures, recruitment manoeuvres, surfactant administration, prone posture, restricted fluid administration, assisted ventilation allowing spontaneous breathing, partial liquid ventilation, administration of pulmonary vasoactive, anti-inflammatory and antioxidant agents are used or considered in the management of ARDS patients. EIT is capable of monitoring the pulmonary effects of many of these therapeutic procedures. This is documented by examples from experimental and clinical EIT studies and by references to relevant EIT literature. The perspectives and limitations of EIT monitoring are also addressed.

System front-end design for concurrent acquisition of electroencephalograms and EIT data

There is recently considerable interest in medical imaging to combine recording of bioelectrical signals with imaging procedures. For example, electroencephalograms (EEGs) recorded during functional magnetic resonance imaging are increasingly being used for neurological and behavioural research. Concurrent acquisition of EEGs and electrical impedance tomography (EIT) data have been suggested as a non invasive technique that could help localize the area of the brain responsible for seizures in epileptic patients awaiting resective surgery. Despite reasonably distinct spectra, EEGs and EIT signals are difficult to record simultaneously because of their very different amplitudes. In this paper, we describe the front-end of a 24-channel system designed to acquire both signals from the same set of scalp electrodes using time-division multiplexing. We have developped a 10-layer 20×15 cm printed circuit board of the front-end and are currently performing circuit characterization tests. System performance parameters and in vivo images will be presented at the conference.

Measuring Breathing Pattern in Patients With Chronic Obstructive Pulmonary Disease by Electrical Impedance Tomography

Background and Objective The measurement of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) by electrical impedance tomography (EIT) requires the use of a mathematical calibration model incorporating not only anthropometric characteristics (previously evaluated in healthy individuals) but probably functional alterations associated with COPD as well. The aim of this study was to analyze the association between EIT measurements and spirometry parameters, static lung volumes, and carbon monoxide diffusing capacity (DLCO) in a group of male patients to develop a calibration equation for converting EIT signals into volume signals. Materials and Methods We measured forced vital capacity (FVC), forced expiratory volume in 1 second (FEV 1), FEV 1/FVC, residual volume, total lung capacity, DLCO, carbon monoxide transfer coefficient (KCO) and standard anthropometric parameters in 28 patients with a FEV 1/FVC ratio of <70%. We then compared tidal volume measurements from a previously validated EIT unit and a standard pneumotachometer. Results The mean (SD) lung function results were FVC, 72 (16%); FEV 1, 43% (14%); FEV1/FVC, 42% (9%); residual volume, 161% (44%); total lung capacity, 112% (17%); DLCO, 58% (17%); and KCO, 75% (25%). Mean (SD) tidal volumes measured by the pneumotachometer and the EIT unit were 0.697 (0.181) L and 0.515 (0.223) L, respectively ( P<.001). Significant associations were found between EIT measurements and CO transfer parameters. The mathematical model developed to adjust for the differences between the 2 measurements ( R 2=0.568; P<.001) was compensation factor=1.81 – 0.82 × height (m) – 0.004×KCO (%). Conclusions The measurement of breathing pattern by EIT in patients with COPD requires the use of a previously calculated calibration equation that incorporates not only individual anthropometric characteristics but gas exchange parameters as well.

Medición del patrón ventilatorio mediante tomografía por impedancia eléctrica en pacientes con EPOC

Background and Objective The measurement of breathing pattern in patients with chronic obstructive pulmonary disease (COPD) by electrical impedance tomography (EIT) requires the use of a mathematical calibration model incorporating not only anthropometric characteristics (previously evaluated in healthy individuals) but probably functional alterations associated with COPD as well. The aim of this study was to analyze the association between EIT measurements and spirometry parameters, static lung volumes, and carbon monoxide diffusing capacity (DLCO ) in a group of male patients to develop a calibration equation for converting EIT signals into volume signals. Materials and Methods We measured forced vital capacity (FVC), forced expiratory volume in 1 second (FEV 1), FEV 1/FVC, residual volume, total lung capacity, DLCO, carbon monoxide transfer coefficient (KCO) and standard anthropometric parameters in 28 patients with a FEV 1/FVC ratio of <70%. We then compared tidal volume measurements from a previously validated EIT unit and a standard pneumotachometer. Results The mean (SD) lung function results were FVC, 72 (16%); FEV 1, 43% (14%); FEV 1/FVC, 42% (9%); residual volume, 161% (44%); total lung capacity, 112% (17%); DLCO, 58% (17%); and KCO, 75% (25%). Mean (SD) tidal volumes measured by the pneumotachometer and the EIT unit were 0.697 (0.181) L and 0.515 (0.223) L, respectively ( P<.001). Significant associations were found between EIT measurements and CO transfer parameters. The mathematical model developed to adjust for the differences between the 2 measurements (R 2=0.568; P<.001) was compensation factor=1.81♯− 0.82♯× height (m)♯−0.004×KCO (%). Conclusions The measurement of breathing pattern by EIT in patients with COPD requires the use of a previously calculated calibration equation that incorporates not only individual anthropometric characteristics but gas exchange parameters as well.

Real-time detection of pneumothorax using electrical impedance tomography*

Pneumothorax is a frequent complication during mechanical ventilation. Electrical impedance tomography (EIT) is a noninvasive tool that allows real-time imaging of regional ventilation. The purpose of this study was to 1) identify characteristic changes in the EIT signals associated with pneumothoraces; 2) develop and fine-tune an algorithm for their automatic detection; and 3) prospectively evaluate this algorithm for its sensitivity and specificity in detecting pneumothoraces in real time. Prospective controlled laboratory animal investigation. Experimental Pulmonology Laboratory of the University of São Paulo. Thirty-nine anesthetized mechanically ventilated supine pigs (31.0 +/- 3.2 kg, mean +/- SD). In a first group of 18 animals monitored by EIT, we either injected progressive amounts of air (from 20 to 500 mL) through chest tubes or applied large positive end-expiratory pressure (PEEP) increments to simulate extreme lung overdistension. This first data set was used to calibrate an EIT-based pneumothorax detection algorithm. Subsequently, we evaluated the real-time performance of the detection algorithm in 21 additional animals (with normal or preinjured lungs), submitted to multiple ventilatory interventions or traumatic punctures of the lung. Primary EIT relative images were acquired online (50 images/sec) and processed according to a few imaging-analysis routines running automatically and in parallel. Pneumothoraces as small as 20 mL could be detected with a sensitivity of 100% and specificity 95% and could be easily distinguished from parenchymal overdistension induced by PEEP or recruiting maneuvers. Their location was correctly identified in all cases, with a total delay of only three respiratory cycles. We created an EIT-based algorithm capable of detecting early signs of pneumothoraces in high-risk situations, which also identifies its location. It requires that the pneumothorax occurs or enlarges at least minimally during the monitoring period. Such detection was operator-free and in quasi real-time, opening opportunities for improving patient safety during mechanical ventilation.

Electrical impedance tomography in extremely prematurely born infants and during high frequency oscillatory ventilation analyzed in the frequency domain

Functional electrical impedance tomography (EIT) measures relative impedance change that occurs in the chest during a distinct observation period and an EIT image describing regional relative impedance change is generated. Analysis of such an EIT image may be erroneous because it is based on an impedance signal that has several components. Most of the change in relative impedance in the chest is caused by air movement but other physiological events such as cardiac activity change in end expiratory level or pressure swings originating from a ventilator circuit can influence the impedance signal. We obtained EIT images and signals in spontaneously breathing healthy adults, in extremely prematurely born infants on continuous positive airway pressure and in ventilated sheep on conventional mechanical or high frequency oscillatory ventilation (HFOV). Data were analyzed in the frequency domain and results presented after band pass filtering within the frequency range of the physiological event of interest. Band pass filtering of EIT data is necessary in premature infants and on HFOV to differentiate and eliminate relative impedance changes caused by physiological events other than the one of interest.

Assessment of the Pulmonary Volume Pulse in Idiopathic Pulmonary Arterial Hypertension by Means of Electrical Impedance Tomography

Background: Electrical impedance tomography (EIT) is a non-invasive imaging technique which can be used to measure the blood volume changes in the pulmonary vascular bed during the cardiac cycle. Study Objectives: This study was performed to evaluate the differences in the EIT signal of the pulmonary vascular bed between healthy subjects and patients with idiopathic pulmonary arterial hypertension (IPAH), who are known to have a remodelled pulmonary vascular bed. Patients and Methods: Twenty-one patients (17 females, 4 males) with IPAH and 30 healthy controls (5 females, 25 males) were measured. EIT measurements were performed in duplicate, on the same day as right heart catheterization to obtain haemodynamic data. The maximal impedance change during systole (Δ Z_sys) was used as a measure of the pulmonary volume pulse and expressed in arbitrary units (AU). Total lung capacity, spirometric values and diffusion capacity for carbon monoxide were measured as well. Results: Mean Δ Z_sys was 215 ± 58 × 10^–2 AU (95% CI 193 × 10^–2 to 236 × 10^–2) in the healthy subjects and 78 ± 27 × 10^–2 AU (95% CI 66 × 10^–2 to 91 × 10^–2) in the IPAH patient group (p < 0.0001). No significant correlation was found between Δ Z_sys and any of the haemodynamic or lung function data. Conclusion: The impedance pulsation of the pulmonary vascular bed is reduced in IPAH in comparison with controls, indicating a reduced volume pulse. This might represent the reduced cross section area, as well as the reduced compliance and number of the pulmonary vessels in these patients.

Pulmonary perfusion measured by means of electrical impedance tomography

Electrical impedance tomography (EIT) is a recent imaging technique based on electrical impedance, offering the possibility of measuring pulmonary perfusion. In the present study the influence of several pulmonary haemodynamical parameters on the EIT signal were investigated. First, the influence on the systolic wave of the EIT signal of stroke volume, large pulmonary artery distensibility (both assessed by means of MRI) and the extent of the pulmonary peripheral vascular bed in 11 emphysematous patients (reduced peripheral vascular bed) and 9 controls (normal peripheral vascular bed) was investigated. Second, the influence of hypoxic pulmonary vasoconstriction on was examined in 14 healthy subjects. Finally, the origin of the diastolic wave was examined in three patients with atrioventricular dissociation. Multiple regression analysis showed that was only dependent on the variable emphysema (p < 0.02), but not dependent on stroke volume (p > 0.3) or pulmonary artery distensibility (p > 0.9). The mean value of for emphysematous patients ( arbitrary units (AU)) was significantly lower (p < 0.001) than in the control group . In the group of healthy subjects decreased significantly (p < 0.001) during hypoxia compared with rest measurements . The absence of the diastolic wave in the cardiological patients suggests the influence of reverse venous blood flow on the EIT signal. It is concluded that volume changes in the small pulmonary vessels contribute significantly to the EIT signal. Moreover, the hypoxia induced decrease in indicates the potential of EIT for measuring pulmonary vascular responses to external stimuli. Keywords: pulmonary perfusion, emphysema, hypoxia, electrical impedance tomography