Objective: Electrical impedance tomography (EIT) involves the application of a small alternating current to produce a series of chest images that can be used to monitor breathing pattern. The relation between chest images and tidal volume has not been sufficiently validated. The aim of the present study was to analyze the correlation between EIT images and the volume-time signal measured with a pneumotachometer in 13 healthy volunteers.
Material and methods: The following measurement devices were used: a) MedGraphics preVent Pneumotach, with special software for recording the volume-time signal (reference test), and b) EIT-4, a fourth-generation prototype unit designed by the Department of Electronic Engineering at the Universidad Politécnica de Cataluña, Spain that records the volume-time signal and produces a graphic depiction of a cross section of the thorax at the sixth intercostal space.
Results: The mean (SD) tidal volume measured by the pneumotachometer and the EIT-4 was 0.523 (0.102) L and 0.527 (0.106) L, respectively (P value not significant). The linear correlation coefficient between the 2 measurements was 0.923 (P=.001), and the mean of the differences between the 2 procedures was -0.003 L (95% confidence interval, -0.045 to 0.038). The greatest differences were associated with female gender, body mass index, and chest circumference. In view of these differences, a different equation based on these variables was needed for calibration of the EIT-4.
Conclusions: The EIT-4 provides an alternative means of monitoring breathing pattern, although a number of issues related to the circumference of the rib cage need to be resolved.