Evaluation of a New Measurement System Combining Body Plethysmography and Electrical Impedance Tomography S. Krueger-Ziolek, Z. Zhao and K. Moeller Institute of Technical Medicine, Furtwangen University, Germany krue@hs-furtwangen.de Abstract: Body plethysmography is a well-established method in pulmonary function diagnosis allowing the analysis of complex and combined ventilation disorders. Lacking information of regional lung ventilation, we combined body plethysmography with electrical imped- ance tomography. We present and evaluate a new meas- urement system including both techniques. First studies indicate that a simultaneous application of both methods is feasible without major interactions. The measurement system enables the assessment of global and regional lung function at the same time, opening new possibilities in diagnosis and prognosis of pulmonary diseases. Keywords: body plethysmography, absolute lung volumes, electrical impedance tomography, regional lung function Introduction Body plethysmography is a common used method of pulmonary function testing allowing the determination of the functional residual capacity (FRCpleth) and the spe- cific airway resistance (sRaw). The airway resistance (Raw) is mathematically equivalent to the ratio of sRaw to FRCpleth [1] and provides information about the sever- ity of airway obstruction [2]. FRCpleth is defined as the volume of intrathoracic gas at end-expiration during tidal breathing [3] and depicts an important parameter in diag- nosis of pulmonary diseases. A typical constant-volume body plethysmograph is a glass- walled and air-tight box featuring the size of a small tele- phone booth with a volume of approximately 700-1000 L [1]. During pulmonary function testing the patient is sitting in the sealed box and breathing in a mouthpiece of a shutter device. Respiratory flow rates and changes in box pressure are measured during tidal breathing to determine sRaw [2]. Occlusion pressure manoeuvres are performed subsequently, whereas the shutter is temporary closed to block the patients’ airflow. Inspiratory and expiratory efforts against the closed shutter lead to decompression and compression of the gas volume in the lung. Pressure variations at the mouth and inside the box occurring under zero-flow conditions are detected and used for determination of FRCpleth [1]. Com- bined with spirometry which allows the measurement of inhaled and exhaled lung volumes [4], absolute lung vol- umes like residual volume (RV) and total lung capacity (TLC) could be assessed. Thus, body plethysmography facilitates the analysis of complex and combined ventila- tion disorders. Although, body plethysmography plays an important part in pulmonary function diagnosis by charac- terizing and identifying the severity of pulmonary disease, information of regional lung function is missing. On the other hand electrical impedance tomography (EIT) is a non-invasive functional imaging technique allowing to trace regional lung ventilation without any radiation expo- sure [5]. The measurement principle of EIT is based on the electrical properties of different biological tissues [6]. The electrical impedance of the lung tissue varies with changes in air content and blood flow [5]. Common EIT systems utilize 16 surface electrodes which are placed around the patients’ thorax and a reference electrode which is connected to the abdomen. Alternating current is induced over one pair of electrodes in a sequential rotating process while the potential differences occurring between adjacent electrode pairs are measured. The electrical potential differences are used to generate EIT images utilizing a reconstruction algorithm [6]. In this paper, we present a new measurement system com- bining body plethysmography and EIT delivering informa- tion on both global and regional lung function. We illustrate the setup of the whole measurement system. Furthermore, we investigated if there are interactions between the two methods affecting each others’ results. Methods The measurement system consists of a constant-volume body plethysmograph (PowerCube-Body+, Ganshorn Medizin Electronic, Germany) and an electrical imped- ance tomograph (PulmoVista 500, Dräger Medical, Ger- many) (Fig.1). Figure 1: Measurement system combining body plethys- mography and electrical impedance tomography. The EIT electrode cables are incorporated in the body plethysmograph through the right glass wall. The elec- trode cables are connected by a plug connector allowing the use of the EIT device outside the box. Biomed Tech 2013; 58 (Suppl. 1) © 2013 by Walter de Gruyter · Berlin · Boston. DOI 10.1515/bmt-2013-4257 Unauthenticated Download Date | 7/27/18 12:27 PM