Electrical impedance tomography applied to assess matching of pulmonary ventilation and perfusion in a porcine experimental model

INTRODUCTION: Electrical 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. METHODS: Six mechanically ventilated, anaesthetised pigs in the supine position were studied at baseline, after inflation of a balloon in the inferior caval vein (B(infl)) to reduce cardiac output and after an increased positive end-expiratory pressure (PEEP) of 20 cmH(2)O (PEEP20) to increase pulmonary aeration. EIT measurements were performed at the mid-thoracic level to measure the amplitude of impedance changes related to ventilation (Z(V)) and perfusion (Z(Q)), both globally and in four defined regions of interest (ROI) extending from the ventral to dorsal distance. RESULTS: A largely parallel distribution of Z(V )and Z(Q )in all four ROIs during baseline conditions corresponded to a bell-shaped frequency distribution of Z(V)/Z(Q )ratios with only moderate scatter. B(infl )and PEEP20 with unchanged tidal volumes significantly increased the mismatch of regional Z(V )and Z(Q), the scatter of Z(V)/Z(Q )ratios and the heterogeneity of the Z(V)/Z(Q )frequency distribution. Significant positive and negative correlations were demonstrated between fractional alveolar dead space (r(2 )= 0.63 [regression coefficient]) and venous admixture (r(2 )= 0.48), respectively, and the global Z(V)/Z(Q )ratio. CONCLUSIONS: EIT may be used to monitor the distribution of pulmonary ventilation and perfusion making detailed studies of V/Q matching possible.