A Numerical Analysis Towards the Continuous Non-invasive Assessment of Intra-Abdominal Pressure in Critical Patients Based on Bioimpedance and Microwave Reflectometry

Intra-abdominal hypertension is produced by an accumulation of liquids in the abdominal cavity. In such case, the overall volume of the abdomen increases, and the abdominal wall is tightened and stretched. Previously, the thickness of the abdominal wall was probed by means of ultrasonic imaging and it showed a decrease as a consequence of the mechanical stress: An inverse correlation between the abdominal wall's thickness and the Intra-Abdominal Pressure is seen on the hypogastrium. The abdominal wall can be modeled as a compound of parallel dielectric slabs, so changes in their width have direct effect on the overall bioimpedance measurements and on the scattering parameters (S11) at higher RF frequencies. Numerical analyses of the bioimpedance and the S11 scattering parameter, as functions of the compression of the abdominal wall, are presented and discussed.