1. The Sheffield electrical impedance tomography system produces information on changes in the distribution of resistivity within tissue. We report on the assessment of electrical impedance tomography in monitoring changes in lung resistivity during a fluid challenge in normal man.

2. Eight normal subjects were studied. Electrical impedance tomography recordings were made at three different lung volumes before, during and after the intravenous infusion of 1 litre of 0.9% NaCl (saline).

3. The mean fall in lung resistivity during the infusion was −22% at total lung capacity (range −10% to −28%), −24% at tidal breathing (−15% to −37%) and −11% at residual volume (-5% to −19%) (P < 0.05 mean pre-infusion resistivity compared with the nadir value after infusion, Wilcoxon).

4. These changes in lung resistivity were probably due to a combination of a fall in haematocrit and an expansion of pulmonary blood volume.

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