Regional Lung Perfusion estimated by Electrical Impedance 1 Tomography in a piglet model of lung collapse 2 3

42 43 The assessment of the regional match between alveolar ventilation and perfusion in 44 critically ill patients requires simultaneous measurements of both parameters. Ideally, 45 assessment of lung perfusion should be performed in real-time with an imaging 46 technology which provides, through fast acquisition of sequential images, information 47 about the regional dynamics or regional kinetics of an appropriate tracer. We present a 48 novel electrical impedance tomography (EIT) based method that quantitatively estimates 49 regional lung perfusion based on first-pass kinetics of a bolus of hypertonic saline 50 contrast. Pulmonary blood flow was measured in six piglets during control and unilateral 51 or bilateral lung collapse conditions. The first-pass kinetics method showed good 52 agreement with the estimates obtained by single-photon-emission computerized 53 tomography (SPECT). The mean difference (SPECT minus EIT) between fractional 54 blood flow to lung areas suffering atelectasis was -0.6 %, with a standard deviation of 2.9 55 %. This method outperformed the estimates of lung perfusion based on 56 impedance-pulsatility. In conclusion, we describe a novel method based on Electrical 57 Impedance Tomography for estimating regional lung perfusion at the bedside. In both, 58 healthy and injured lung conditions, the distribution of pulmonary blood flow as assessed 59 by EIT agreed well with the one obtained by SPECT. The method proposed in this paper 60 has the potential to contribute to a better understanding of the behavior of regional 61 perfusion under different lung and therapeutic conditions. 62 63