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 (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.