Electrical impedance tomography: New diagnostic possibilities using regional time constant maps

Pulmonary function tests are used to assess the severity of obstructive and restrictive lung diseases. These tests provide information on the whole lung considered as one compartment and can be used to globally describe the physical properties of flow resistance R and compliance C, but do not yield regional information. Electrical impedance tomography (EIT) is widely used in clinical research regarding ventilation monitoring. In this study, EIT recordings were performed simultaneously with spirometry during a forced expiration maneuver. We could show that EIT provides similar results to describe pulmonary mechanics. Therefore, seven patients (814 years) with asthma bronchiale were examined before and after therapy with Salbutamol to perform broncho spasmolysis. We found a relation between flow resistance R and global time constant τglobal with positive correlation r=0.88. Additionally, we propose the use of the regional time constant τreg(x) (RTC-map) as a new imaging modality in a case study which demonstrates its performance considering broncho spasmolysis.