System introduction and evaluation of the first Chinese chest EIT device for ICU applications

Abstract

Chest electrical impedance tomography (EIT) is a promising application which is used to monitor the ventilation and perfusion of the lung at the bedside dynamically. The aim of the study was to introduce the first Chinese made chest EIT device for ICU application (Pulmo EIT-100). The system design of the hardware and software was briefly introduced. The performance of the system was compared to PulmoVista 500 (Dräger Medical) in healthy volunteers. The EIT system Pulmo EIT-100 consists of impedance measurement module, power supply module, PC all-in-one machine, medical cart and accessories. The performance of the system current source and voltage measurement unit was tested. A total of 50 healthy lung volunteers were prospectively examined. Subjects were asked to perform repetitive slow vital capacity (SVC) maneuvers with a spirometer. EIT measurements were performed in the following sequence during each SVC with: (1) Pulmo EIT-100, (2) PulmonVista500, (3) Pulmo EIT-100 and (4) PulmonVista500. Linearity and regional ventilation distribution of the reconstructed images from two devices were compared. The output frequency stability of the current source was 2 ppm. The amplitude error within one hour was less than 0.32‰. The output impedance of the current source was about 50kΩ. The signal-to-noise ratio of each measurement channel was ≥ 60 dB. For fixed resistance measurements, the measured values drifted about 0.08% within one hour. For human subjects, the correlations between the spirometry volume and EIT impedance from two devices were both 0.99 ± 0.01. No statistical significances were found in the parameters investigated. The repeatability (variability) of measures from the same device was comparable. Our EIT device delivers reliable data and might be used for patient measurement in a clinical setting.

Figure 1

Overall design of the system. PC personal computer, ADC analog–digital converter, PGA programmable gain amplifier, MCU microcontroller unit, In-Amp instrumentation amplifier.

Figure 2

Screenshot of the software display.

Figure 3

Illustration of the VCCS module circuit principle.

Figure 4

Illustration of the measurement sequence and relative impedance changes. First row, relax tidal breaths and slow vital capacity maneuvers recorded with a spirometer. Second row, impedance-time curves during the SVC maneuver. Third row, correlation between the spirometry volume and EIT impedance changes. Fourth row, impedance variation during SVC. AU, arbitrary unit. PV500 PulmoVista 500, PE100 PulmoEIT-100.

Figure 5

Bland–Altman plots compared the EIT-based measures calculated with PE100 (Pulmo EIT-100, FMMU) and the PV500 (PulmoVista500, Dräger). TV tidal impedance variation, SVC impedance variation during SVC maneuver, GI the global inhomogeneity index, CoV center of ventilation, RVD regional ventilation delay.