When treating patients with dyspnoea, conventional diagnostic tools (computed tomography, spirometry, body plethysmography) often fail to detect pathological changes, making it difficult for the treating physician to choose an appropriate therapeutic approach. Therefore, it would be desirable to have an examination method that reveals the pulmonary changes in postacute Corona-Virus-Disease-2019 (COVID-19) syndrome patients that remain hidden from other diagnostic procedures.~Electrical impedance tomography (EIT) is a non-invasive and radiation-free imaging technique that can show the regional ventilation of the lungs almost in real-time based on the changes in the electrical impedance of the thorax during inspiration and expiration. This method is based on the observation that the electrical conductivities of biological tissues vary considerably depending on their nature and functional state. Clinical questions in which the inhomogeneity of lung ventilation is to be analysed (e.g., under- or overinflation of individual lung areas, lung collapse, etc.) can be investigated particularly well with EIT since intrathoracic impedance changes correlate strongly with changes in regional lung ventilation.~Up to now, EIT has mainly been used as a monitoring method in intensive care medicine to adapt ventilation settings and other therapeutic measures to the individual needs of patients. In this field, the method has proven useful for obtaining an overview of the distribution of a respiratory volume in a transverse EIT slice, comparing different lung regions, identifying inhomogeneities and assessing regional ventilation during spontaneous breathing.~The aim of this case-control study is to use EIT data obtained during routine examinations of post-COVID patients to analyse whether EIT is suitable as a radiation-free, non-invasive imaging technique for assessing regional ventilation of the lung in spontaneously breathing post-COVID patients and whether additional evidence of regional ventilation disorders in these patients can be found by determining lung ventilation using EIT. As there are no reference data from spontaneously breathing lung-healthy patients so far, a reference group will be generated whose EIT data will be compared with those of post-COVID patients.
In the absence of data on Electric impedance tomography of healthy spontaneous breathing patients that is compared to dyspnoeic patients suffering from postacute COVID-19 syndrome, the investigators contend that electrical impedance tomography provides additional clues to visualize regional lung ventilation and differentiate healthy from sick patients.