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

Abstract

Intrathoracic ventilation related and pulsatile (perfusion) impedance changes can be measured by the noninvasive and radiation-free imaging method Electrical Impedance Tomography (EIT). Ventilation monitoring is still the key research area in EIT, whereby perfusion monitoring gain more and more in interest. However, there are still many unknown influencing factors concerning pulsatile impedance measurements which have to be investigated. Hence, in this observational case study the impact of prolonged apnea periods on pulsatile impedance changes was examined in a patient with suspected brain death undergoing several apnea tests. In addition, the correlation between changes in pulsatile impedance and certain blood gas parameters (carbon dioxide partial pressure, pCO2; oxygen partial pressure, pO2; pH; bicarbonate, HCO3 -) were explored. Results show that the pulsatile impedance signal changes over time during apnea. An increase in the area under the curve (Mean AuC) and the maximum amplitude (Mean Max) of heart beat associated impedance signals was observed (Mean AuC: up to 65 %; Mean Max: up to 57 %). Furthermore, a positive correlation between the increase in impedance and pCO2and HCO3 - was assessed (both: up to 0.99), whereas pO2and pH show a negative correlation (both: up to -0.99). These preliminary results indicate that pulsatile EIT monitoring may be applied to get additional information regarding cardio-pulmonary interactions sustaining diagnosis or treatment of lung diseases.

Keywords

• electrical impedance tomography
• pulsatile impedance changes
• apnea
• blood gas analysis