Changes in hemodynamics and aortic volume as assessed with a dual-Doppler system

The esophageal Doppler monitor (EDM) is a minimally-invasive device to measure aortic blood flow and quantify hemodynamics in patients. A modified dual-Doppler EDM, combined with pressure measurements, allows for measurement of aortic volume via the Bramwell-Hill equation. An in-vitro flow system was developed to model the cardioaortic circulation. This system consists of a pump to expel a viscous fluid through a thin-walled latex tube, to models the aorta, and stiff tubes to complete the flow loop and add ldquoperipheralrdquo resistance. Doppler analysis by Matlab programming yields critical hemodynamic parameters including pulse wave velocity (PWV), stroke volume (SV), pulse pressure (PP), heart rate (HR) and compliance (C) which combine to yield the Bramwell-Hill tube volume (V_BH). Comparing calculated variables with in-vitro measurements at HRs of 50, 60 and 72 BPM established accuracy of plusmn4.5% (n=5) for SV and reproducibility for PWV of plusmn 20% (n=8). As PP increased, a decreasing C was observed. Results suggest changes in V_BH are more sensitive to changes in HR and cardiac output than PP alone. Therefore, V_BH may be a sensitive indicator of aortic volume changes (due to bleeding and changes in fluid status). The dual-Doppler technique demonstrated an accurate and reproducible method to monitor hemodynamics.