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

Abstract

Abstract Background Electrical impedance tomography (EIT) generates images of the lungs based on impedance change and was able to detect changes in airflow after histamine challenge in horses. Objectives To confirm that EIT can detect histamine‐provoked changes in airflow and subsequent drug‐induced bronchodilatation. Novel EIT flow variables were developed and examined for changes in airflow. Methods Bronchoconstriction was induced using stepwise histamine bronchoprovocation in 17 healthy sedated horses. The EIT variables were recorded at baseline, after saline nebulization (control), at the histamine concentration causing bronchoconstriction (Cmax) and 2 and 10 minutes after albuterol (salbutamol) administration. Peak global inspiratory (PIFEIT) and peak expiratory EIT (PEFEIT) flow, slope of the global expiratory flow‐volume curve (FVslope), steepest FVslope over all pixels in the lung field, total impedance change (surrogate for tidal volume; VTEIT) and intercept on the expiratory FV curve normalized to VTEIT (FVintercept/VTEIT) were indexed to baseline and analyzed for a difference from the control, at Cmax, 2 and 10 minutes after albuterol. Multiple linear regression explored the explanation of the variance of Δflow, a validated variable to evaluate bronchoconstriction using all EIT variables. Results At Cmax, PIFEIT, PEFEIT, and FVslope significantly increased whereas FVintercept/VT decreased. All variables returned to baseline 10 minutes after albuterol. The VTEIT did not change. Multivariable investigation suggested 51% of Δflow variance was explained by a combination of PIFEIT and PEFEIT. Conclusions and Clinical Importance Changes in airflow during histamine challenge and subsequent albuterol administration could be detected by various EIT flow volume variables.

Keywords

• albuterol
• equine
• equine asthma
• flow volume loop
• flowmetric plethysmography
• pulmonary function test