Abstract

IntroductionElectrical impedance tomography (EIT) can be used to measure impedance changes related to the thoracic content of air and blood. Few studies, however, have utilised EIT to make concurrent measurements of ventilation and perfusion. This experimental study was performed to investigate the feasibility of EIT to describe ventilation/perfusion (V/Q) matching after acute changes of pulmonary perfusion and aeration.MethodsSix mechanically ventilated, anaesthetised pigs in the supine position were studied at baseline, after inflation of a balloon in the inferior caval vein (Binfl) to reduce cardiac output and after an increased positive end-expiratory pressure (PEEP) of 20 cmH2O (PEEP20) to increase pulmonary aeration. EIT measurements were performed at the mid-thoracic level to measure the amplitude of impedance changes related to ventilation (ZV) and perfusion (ZQ), both globally and in four defined regions of interest (ROI) extending from the ventral to dorsal distance.ResultsA largely parallel distribution of ZV and ZQ in all four ROIs during baseline conditions corresponded to a bell-shaped frequency distribution of ZV/ZQ ratios with only moderate scatter. Binfl and PEEP20 with unchanged tidal volumes significantly increased the mismatch of regional ZV and ZQ, the scatter of ZV/ZQ ratios and the heterogeneity of the ZV/ZQ frequency distribution. Significant positive and negative correlations were demonstrated between fractional alveolar dead space (r2 = 0.63 [regression coefficient]) and venous admixture (r2 = 0.48), respectively, and the global ZV/ZQ ratio.ConclusionsEIT may be used to monitor the distribution of pulmonary ventilation and perfusion making detailed studies of V/Q matching possible.

Highlights

  • Electrical impedance tomography (EIT) can be used to measure impedance changes related to the thoracic content of air and blood

  • balloon in the inferior caval vein (Binfl) and PEEP from to 20 cmH2O (PEEP20) with unchanged tidal volumes significantly increased the mismatch of regional ZV and ZQ, the scatter of ZV/ZQ ratios and the heterogeneity of the ZV/ZQ frequency distribution

  • EIT may be used to monitor the distribution of pulmonary ventilation and perfusion making detailed studies of V/Q matching possible

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Summary

Introduction

Electrical impedance tomography (EIT) can be used to measure impedance changes related to the thoracic content of air and blood. Electrical impedance tomography (EIT) is a non-invasive, nonradiant, continuous technique that can be used to perform bedside measurements of impedance changes related to the thoracic content of air and blood [1,2]. We recently described how EIT can be used to monitor beatto-beat changes in global pulmonary perfusion with adequate precision during acute variations in stroke volume related to changes in cardiac preload of pulmonary and extra-pulmonary origin [14]. This was performed by applying short periods of apnoea. The present investigation was designed to assess the matching of ventilation and perfusion, as reflected by the ventilation/perfusion (V/Q) ratio derived from EIT measurements

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