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

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 (C(max)) and 2 and 10 minutes after albuterol (salbutamol) administration. Peak global inspiratory (PIF(EIT)) and peak expiratory EIT (PEF(EIT)) flow, slope of the global expiratory flow‐volume curve (FV(slope)), steepest FV(slope) over all pixels in the lung field, total impedance change (surrogate for tidal volume; VT(EIT)) and intercept on the expiratory FV curve normalized to VT(EIT) (FV(intercept)/VT(EIT)) were indexed to baseline and analyzed for a difference from the control, at C(max), 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 C(max), PIF(EIT), PEF(EIT), and FV(slope) significantly increased whereas FV(intercept)/VT decreased. All variables returned to baseline 10 minutes after albuterol. The VT(EIT) did not change. Multivariable investigation suggested 51% of Δflow variance was explained by a combination of PIF(EIT) and PEF(EIT). CONCLUSIONS AND CLINICAL IMPORTANCE: Changes in airflow during histamine challenge and subsequent albuterol administration could be detected by various EIT flow volume variables.