Impact of lung volume changes on perfusion estimates derived by Electrical Impedance Tomography

Abstract

Electrical Impedance Tomography (EIT), an imaging technique which operates non-invasively and without radiation exposure, provides information about ventilation- and cardiac-synchronous (pulsatile) changes in the lung. It is well known, that perfusion within the thorax is influenced by lung volume or intrathoracic pressure. In this observational study, it shall be investigated if this phenomenon can be monitored by EIT. Therefore, the impact of the amount of air within the lung on the pulsatile EIT signal was evaluated by carrying out EIT measurements with a spontaneously breathing lung healthy subject holding the breath at three different inspiratory and three various expiratory volume levels during normal tidal breathing. For EIT data analysis, a region of interest was defined by including lung tissue and excluding the heart region. The EIT data revealed, that the shape and the amplitude of the pulsatile EIT signal (evaluated per heartbeat) during the phases of breath holding were dependent on the enclosed lung volume. For lung volumes > 4 L, the amplitude of the pulsatile EIT signal increased with rising inspiratory level and the shape remained almost unchanged. For lung volumes < 4 L, a change in shape was visible but the amplitude remained more or less the same with decreasing expiratory level. Since the results of this observational study show that the pulsatile EIT signal is influenced by the lung volume, it might be used in future to draw conclusions of cardiacpulmonary interactions or intrathoracic pressure states, benefitting the treatment of intensive care patients.

EIT based intrathoracic pulsatile impedance measurements during apnea: a case study

“…Additionally, each EIT signal section was separated into smaller signal segments corresponding to one heart beat ( Figure 2). A linear trend between the start and end point of each signal segment was removed as well as an interpolation of each signal segment to the mean length of all signal segments was conducted (refer to [4]). Subsequently, for each 2 to 3 minutes section, the mean signal of all signal segments was calculated ( Figure 2).…”

“…In a previous study, we assessed changes in the pulsatile impedance signal depending on lung volume during breath holding (approx. 10 seconds) in a spontaneously breathing subject [4]. It was indicated that shape and amplitude of the pulsatile impedance signal varied based on changes in lung volume.…”