Evaluation of histamine‐provoked changes in airflow using electrical impedance tomography in horses

Abstract

Background Electrical impedance tomography (EIT) generates thoracic impedance images of the lungs and has been used to assess ventilation in horses. This technique may have application in the detection of changes in airflow associated with equine asthma. Objectives The objective was to determine if histamine‐induced airflow changes observed with flowmetric plethysmography (Δflow) could also be explained using global and regional respiratory gas flow signals calculated from EIT signals. Study design Experimental in vivo study. Methods Six horses, sedated using detomidine were fitted with a thoracic EIT belt and flowmetric plethysmography hardware. Saline (baseline = BL) and increasing concentrations of histamine (C1‐4) were nebulised into the face mask until a change in breathing pattern was clinically confirmed and Δflow increased greater or equal to 50%. After nebulisation Δflow and EIT images were recorded over 3 minutes and peak global inspiratory (InFglobal) and expiratory (ExFglobal) flow as well as peak regional expiratory and inspiratory flow for the dorsal and the ventral area of the right and left lungs were evaluated. Delta flow, InFglobal and ExFglobal at subsequent concentrations were indexed to baseline (yi = Ci/BL−1). Indexed and nonindexed variables were evaluated for a difference from baseline at sequential histamine doses (time). Multiple linear regression assessment of variance in delta flow was also investigated. Results Consistent with histamine‐provoked increases in Δflow, the global flow indices increased significantly. A significant increase in regional inspiratory flow was seen in the right and left ventral lung and dorsal right lung. Multiple regression revealed that the variance in ExFglobal, and right and left ventral expiratory flow best explained the variance in Δflow (r2 = .82). Main limitations Low number of horses and horses were healthy. Conclusions Standardised changes in airflow during histamine challenge could be detected using EIT gas flow variables.

Can bronchoconstriction and bronchodilatation in horses be detected using electrical impedance tomography?

“…Previous studies have identified unchanging tidal volumes during bronchoconstriction in horses. 11,25,26 The respiratory rate increased with histamine and then decreased with albuterol, whereas tidal volume did not change significantly, indicating an increase and then subsequent decrease in minute ventilation. The observed increase in respiratory rate results in a decrease in inspiratory 24,25 and expiratory time, 24 which leads to the measured increase in flow variables at stable tidal volume.…”

“… 10 From the flow signal, global peak inspiratory (PIF EIT ) and global peak expiratory (PEF EIT ) flow were calculated for the whole lung for each breath. 11 …”

“… 10 Electrical impedance tomography derived flow signals have been shown to detect changes in airflow during histamine bronchoprovocation in horses. 11 In that pilot study, flowmetric plethysmography (FP) described by the variable delta flow (Δflow) was compared against regional and global peak inspiratory and expiratory flow variables calculated from the EIT measurements. Although EIT flow variables and Δflow represent different measurement principles of flow, EIT flow variables were shown to follow the same pattern of change as Δflow over the duration of the histamine challenge.…”

Design and Optimization of a Finite Element Model for Electrical Resistance Tomography of Human Lungs

“…Based on the different electrical features of the object in the sensitivity field, the ET techniques could be divided into electromagnetic tomography (EMT), electrical capacitance tomography (ECT), electrical impedance tomography (EIT), and electrical resistance tomography (ERT). Based on the principle of electromagnetic induction, the EMT can reconstruct the distribution state of the magnetic permeability for the medium in the sensitivity field [1][2][3][4][5][6]; Based on the principle of capacitance sensitivity, the ECT can reconstruct the distribution state of the dielectric constant for the medium in the sensitivity field [7][8][9][10][11][12][13][14][15][16][17]; Based on the principle of impedance sensitivity, the EIT can reconstruct the distribution state of the complex admittance for the medium in the sensitivity field [18][19][20][21][22][23][24]; Based on the principle of resistance sensing, the ERT can reconstruct the distribution state of the dielectric resistivity/conductivity for the medium in the sensitivity field [25][26][27][28][29][30].…”

Width Optimization of Array Electrode for Human Lung Electrical Resistance Tomography System Based on prior Knowledge

“…Electrical tomography (ET) technology consists of 4 different branches, namely, electrical impedance tomography (EIT) [8][9][10][11][12][13][14], ERT [15][16][17][18][19][20], electrical capacitance tomography (ECT) [21][22][23][24][25][26][27], and electromagnetic tomography (EMT) [28][29][30][31][32][33], among which the ERT technology is a new generation of medical imaging technology and a simplified form of the EIT technology when only the change of conductivity/resistivity of the sensitive field is considered, having three outstanding advantages of functional imaging, no damage, and medical image monitoring. Compared with other monitoring methods, ERT technology has incomparable advantages in real-time monitoring and quantitative evaluation of critical respiratory diseases.…”