Bedside and continuous assessment of arterial load in critically-ill patients by combined analysis of esophageal doppler blood flow and arterial pressure waveform: preliminary results
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KeywordsReflection Coefficient Input Impedance Characteristic Impedance Arterial Compliance Continuous Assessment
Because the oscillatory nature of the arterial pressure and blood flow, the input impedance assessed in frequency domain provides the best description of the arterial load . However, this approach is complex and not feasible in clinical practice. Nowadays, it is possible to measure simultaneously flow and pressure at the bedside using minimally invasive monitoring.
To test the usefulness of continuous assessment of arterial load based on a 3-element Windkessel model by a combined analysis of the esophageal Doppler derived-blood flow and arterial pressure waveform, against standard frequency-domain analysis of arterial impedance.
Ten measurements in 6 patients were obtained. Time and frequency-domain derived Zc were similar at pre(222 vs 203 dyn•s•cm-5; P = n.s.) and post-intervention (205 vs 165 dyn•s•cm-5; P = n.s.). Pre and post-intervention values and percentage changes of Zc and Zct were strongly correlated (R2 = 0.94, R2 = 0.95; R2 = 0.96; P < 0.0001). Time and frequency-domain derived reflection coefficient were also correlated at pre (R2 = 0.93; P < 0.0001), post-intervention (R2 = 0.85; P < 0.0001) and percentage changes (R2 = 0.85; P < 0.0001). Changes in net arterial compliance and Z1 were also inversely correlated (R2 = 0.59; P < 0.0001). As expected, Z0 and R showed an equivalent behavior.
Our preliminary results shows that continuous and noninvasive assessment of different aspects of arterial load by combined analysis of Doppler derived-aortic blood flow and arterial pressure could be feasible at the bedside and comparable to standard frequency domain analysis.
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