Non-invasive stroke volume assessment using the thoracic electrical bioimpedance

Impedance cardiography provides the possibility to estimate the stroke volume using an alternating current injected into the body. This thesis presents new research in this field. A new application area in medical care is introduced in the form of a wearable impedance cardiograph integrated into a shirt for home monitoring. Therefore, conductive textile materials were used as electrodes and electrical wiring in a garment. The garment provides a connection to a lightweight hardware which transmits the data wirelessly. Thus, monitoring patients 24/7 is possible. In addition, physiological sources contributing to the impedance waveform were analyzed using a 4D model of the human thorax and FEM simulations. The results show that blood conductivity changes due to red blood cell orientation are the major contributor to the impedance signal. The second factor is aortic wave propagation. With this model, negative influences of heart failure on the measured impedance were identified. These results were verified by results obtained from clinical trials: a recompensation study and a pleural drainage study. It was shown that with increasing lung conductivity due to lung edema or pleural effusion, the impedance decreases, leading to a lower stroke volume. Furthermore, improved algorithms (discrete wavelet transform) to assess characteristic points in the impedance cardiogram were introduced, performing better than those in a commercially available reference device. Last but not least, completely new application areas were made accessible by human trials. The feasibility of impedance cardiography to estimate the blood alcohol content was analyzed, showing promising results. In addition, the stroke volume of sport divers was assessed to characterize different stages of apnea.