Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography

Abstract

Introduction: Electrical impedance tomography (EIT) has been shown to be able to distinguish both ventilation and perfusion. With adequate filtering the regional distributions of both ventilation and perfusion and their relationships could be analysed. Several methods of separation have been suggested previously, including breath holding, electrocardiograph (ECG) gating and frequency filtering. Many of these methods require interventions inappropriate in a clinical setting. This study therefore aims to extend a previously reported frequency filtering technique to a spontaneously breathing cohort and assess the regional distributions of ventilation and perfusion and their relationship. Methods: Ten healthy adults were measured during a breath hold and while spontaneously breathing in supine, prone, left and right lateral positions. EIT data were analysed with and without filtering at the respiratory and heart rate. Profiles of ventilation, perfusion and ventilation/perfusion related impedance change were generated and regions of ventilation and pulmonary perfusion were identified and compared. Results: Analysis of the filtration technique demonstrated its ability to separate the ventilation and cardiac related impedance signals without negative impact. It was, therefore, deemed suitable for use in this spontaneously breathing cohort. Regional distributions of ventilation, perfusion and the combined ΔZ V /ΔZ Q were calculated along the gravity axis and anatomically in each position. Along the gravity axis, gravity dependence was seen only in the lateral positions in ventilation distribution, with the dependent lung being better ventilated regardless of position. This gravity dependence was not seen in perfusion. When looking anatomically, differences were only apparent in the lateral positions. The lateral position ventilation distributions showed a difference in the left lung, with the right lung maintaining a similar distribution in both lateral positions. This is likely caused by more pronounced anatomical changes in the left lung when changing positions.

Toward Morphological Thoracic EIT: Major Signal Sources Correspond to Respective Organ Locations in CT

“…However, similar, sometimes multiple, oppositephase peaks were subsequently found in other animals, e.g., the one presented in Fig. 9, but they were usually much weaker and located outside the heart area as segmented from CT. A similar phenomenon can be observed in the results reported in [10]. We therefore speculate that this effect is associated with the movement of the heart wall at the heart-lung interface.…”

“…We therefore speculate that this effect is associated with the movement of the heart wall at the heart-lung interface. By comparing with ECG the phase of the weak cardiac frequency observed within the lung ROI (found to be delayed with respect to changes in the heart ROI), it has previously been demonstrated that they represent changes in blood volume [10]. However, the opposite-phase (rather than just delayed) features around the heart, and more specifically the very clear lines which separate them, have not so far been explored (to the best of the authors' knowledge) and may prove a useful feature for further improving the delineation of the heart within thoracic EIT images.…”

“…Thresholds then define ROIs with significant ventilation. Pulletz et al [18] showed that both methods give similar results and have since often been used, with slight modification [10], [18]. However, since the most commonly used reconstruction algorithms produce EIT images that are circular, and thus do not correspond to the anatomy, none of these methods could be validated against a morphological medical imaging modality.…”

Perspectives in respiratory monitoring

“…Pour pallier à ce problème, l'analyse des données n'est souvent réalisée que sur les voxels dans lesquels l'écart-type de ΔZ dépasse 20-35 % de son maximum sur l'image d'EIT-f [20] (les voxels dont la variabilité est inférieure sont considérés comme non ventilés, mais peuvent contenir du poumon dérecruté, de la paroi thoracique ou du médiastin). Malgré l'exclusion de ces voxels, le médiastin est souvent inclus dans les régions d'intérêts pulmonaires en raison de la transmission des mouvements respiratoires par contiguïté, et des techniques d'analyse utilisant l'analyse spectrale ont été récemment proposées pour pallier à ce problème [21,22]. Enfin, la TIE ne permet d'explorer qu'une zone limitée du poumon (coupe transversale de 5 cm d'épaisseur environ), dont les caractéristiques évaluées en TIE peuvent différer du reste du parenchyme.…”

Breath detection using short-time Fourier transform analysis in electrical impedance tomography

“…Numerous studies have been published in lung function monitoring for adults [1][2][3][4][5][6]. However, assessment of lung function in pediatric population is more challenging due to the patient movements and artifacts which have come under investigation only recently [7][8][9][10].…”