Ventilation Inhomogeneity Assessed by Electrical Impedance Tomography

Abstract

Postural changes exert an effect on the distribution of pulmonary ventilation. So far, the studies with help of electrical impedance tomography (EIT) analyze this effect based on comparing relative impedance values in different geometric regions of interest. The aim of this prospective study was to assess the postural effect on ventilation distribution by an EIT-based new tool: the global inhomogeneity (GI) index. Totally nine human subjects were studied in a tilt-table test for upright and supine position during spontaneous tidal breathing. The subjects were monitored by EIT and continuous blood pressure measurement. End-expiratory lung volume and tidal volume are significantly lower in supine position. In supine position, the ventilation may be higher in the dorsal lung regions when compared with the ventral ones due to gravity. However, there was no significant difference in ventilation inhomogeneity (indicated by GI index) in the subjects between the two positions. We conclude that with respect to ventilation inhomogeneity, gravitation is not a major concern in healthy spontanously breathing subjects. The GI index may become a useful online tool at the bedside that focuses on monitoring the whole ventilation distribution outcome for intensive care patients with severe pulmonary disease.