A ventilatable physical four compartment model of the rat thorax for electrical impedance tomography

Objective.Electrical impedance tomography (EIT) has become an important means for gaining enhanced insights into respiratory system mechanics, particularly in research on the conditions of the lungs during mechanical ventilation. For further development of EIT based research regarding the respiratory system, animal experiments play a crucial role.Approach.Focussing on reduction of small animal experiments, we built a physical EIT model of the rat thorax for potential setup development and standardised algorithm testing. The model contains four separately ventilatable compartments, aiming to represent ventilation in the ventral-right, ventral-left, dorsal-right and dorsal-left regions of interest (ROI) of the EIT image. The model was connected to an EIT device and ventilated with a variety of tidal volumes and respiratory rates with all combinations of connected compartments. Thereby, airway pressure and flow were measured to determine the mechanical properties of the physical model.Main results.EIT measurements confirmed the localisation of the four compartments in the desired ROI and connecting/disconnecting individual compartments ventilation resulted in corresponding changes in the regional tidal impedance variation. The physical model had a compliance of 146 ± 5μl/cmH₂O when four compartments were ventilated at a respiratory rate of 30 1 min^-1. Respiratory system compliance decreased when ventilation was restricted to fewer ventilated compartments. The compliance was comparable for all tested tidal volumes but decreased with increasing respiratory rate.Significance.We present a ventilatable four compartment EIT model of the rat thorax that is capable of simulating regional ventilation. The respiratory system mechanics of the model reflect mechanics comparable to mechanically ventilated lung injured rats including viscoelastic behaviour, as indicated by the dependency of respiratory system compliance on respiratory rate. While this model is not a substitute forin vivopathophysiological studies, it may be useful for reducing small animal experiments when testing setups or experimental procedures, and may further allow to generate reproducible data for standardised algorithm testing.