The usefulness of electrical impedance tomography (EIT) to assess ventilation-related phenomena in the thorax has already been demonstrated, especially in controlled environments. We focus on our developments in the assessment of the unilateral pulmonary function (UPF) in real clinical environments. The impact of the reduction of the number of electrodes used is analysed theoretically and experimentally with different approaches. Sixteen-electrode EIT measurements were performed on a group of lung cancer patients (19 M, 2 F, ages 25-77 years). Results are compared with those obtained from ventilation scintigraphy. Eight-electrode measurements were synthesized from the 16-electrode ones. The Bland and Altman analysis indicates an agreement of about +/- 1 percent points in the estimation of UPF. On five of these patients real 8-electrode measurements were performed, obtaining differences from 0.2 percent to 6 percent points. It is concluded that reducing the number of electrodes does not adversely affect the assessment of UPF, but there is a reproducibility issue affecting all the techniques which needs further study.